2022-08-06 93e038f01209282f8771b7cf9df85c5c 99+ 21 分钟 3.1 k

应用进程Context创建流程(转)

今天讲讲应用进程Context的创建流程，相信大家平时在开发过程中经常会遇到对Context对象的使用，Application是Context，Activity是Context，Service也是Context，所以有一个经典的问题是一个App中一共有多少个Context？

这个问题的答案是Application + N个Activity + N个Service。

还有就是我们平时在使用Context过程中许多时候由于使用不当，可能会造成内存泄露的情况等等，这个也是需要我们注意的。这里有篇不错的文章：
Android Context 是什么？

好吧，什么叫应用进程Context呢？这是指的是Application所代表的Context的创建流程，还记得我们前几篇写的应用进程创建流程么？
android源码解析之（十一）–>应用进程启动流程
最后我们得出结论，应用进程的起始方法是ActivityThread.main方法，好吧，

由于还未讲解Service相关知识，这里暂时讲解一下Activity与Application中Context对象的创建过程。

首先我们就从ActivityThread.main方法开始看一下Application的创建流程。。。

public static void main(String[] args) {
        ...
        ActivityThread thread = new ActivityThread();
        thread.attach(false);
        ...
    }

这里我们发现在方法体中我们创建了一个ActivityThread对象并执行了attach方法：

private void attach(boolean system) {
        sCurrentActivityThread = this;
        mSystemThread = system;
        if (!system) {
            ViewRootImpl.addFirstDrawHandler(new Runnable() {
                @Override
                public void run() {
                    ensureJitEnabled();
                }
            });
            android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
                                                    UserHandle.myUserId());
            RuntimeInit.setApplicationObject(mAppThread.asBinder());
            final IActivityManager mgr = ActivityManagerNative.getDefault();
            try {
                mgr.attachApplication(mAppThread);
            } catch (RemoteException ex) {
                // Ignore
            }
            // Watch for getting close to heap limit.
            BinderInternal.addGcWatcher(new Runnable() {
                @Override public void run() {
                    if (!mSomeActivitiesChanged) {
                        return;
                    }
                    Runtime runtime = Runtime.getRuntime();
                    long dalvikMax = runtime.maxMemory();
                    long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
                    if (dalvikUsed > ((3*dalvikMax)/4)) {
                        if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
                                + " total=" + (runtime.totalMemory()/1024)
                                + " used=" + (dalvikUsed/1024));
                        mSomeActivitiesChanged = false;
                        try {
                            mgr.releaseSomeActivities(mAppThread);
                        } catch (RemoteException e) {
                        }
                    }
                }
            });
        } else {
          ...  
        }
    }

这里看一下重点实现，我们可以发现在方法体中调用了ActivityManagerNative.getDefault().attachApplication(mAppThread)
看过我的前几篇文章的童鞋应该知道这里就是一个Binder进程间通讯，其实上执行的是ActivityManagerService.attachApplication方法，具体的可以参考前几篇文章的介绍，好吧，既然这样我们看一下ActivityManagerService.attachApplication方法的具体实现。

Android基础

Android ActivityManagerNative Zygote SystemServer 安装流程

2022-08-06

2022-08-06 a69c1dce0de44b341229ed40f951888c 99+ 19 分钟 2.8 k

activity销毁流程(转)

继续我们的源码解析，上一篇文章我们介绍了Activity的启动流程，一个典型的场景就是Activity a 启动了一个Activity b，他们的生命周期回调方法是：
onPause(a) –> onCreate(b) –> onStart(b) –> onResume(b) –> onStop(a)
而我们根据源码也验证了这样的生命周期调用序列，那么Activity的销毁流程呢？它的生命周期的调用顺序又是这样的呢？

这里我们我做一个简单的demo，让一个Activity a启动Activity b，然后在b中调用finish()方法，它们的生命周期执行顺序是：

onPause(b)
onRestart(a)
onStart(a)
onResume(a)
onStop(b)
onDestory(b)

好吧，根据我们测试的生命周期方法的回调过程开始对Activity销毁流程的分析，一般而言当我们需要销毁Activity的时候都会调用其自身的finish方法，所以我们的流程开始是以finish方法开始的。

一：请求销毁当前Activity

MyActivity.finish() Activity.finish() ActivityManagerNative.getDefault().finishActivity() ActivityManagerService.finishActivity() ActivityStack.requestFinishActivityLocked() ActivityStack.finishActivityLocked() ActivityStack.startPausingLocked()

Android基础

Android ActivityManagerNative Zygote SystemServer 安装流程

阅读更多>>

2022-08-06

2022-08-06 68985601b51952c0fcc14a4e1dd302fd 99+ 1 小时 10.3 k

activity启动流程(转)

好吧，终于要开始讲解Activity的启动流程了，Activity的启动流程相对复杂一下，涉及到了Activity中的生命周期方法，涉及到了Android体系的CS模式，涉及到了Android中进程通讯Binder机制等等，

首先介绍一下Activity，这里引用一下Android guide中对Activity的介绍：

An activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Although the activities work together to form a cohesive user experience in the email application, each one is independent of the others. As such, a different application can start any one of these activities (if the email application allows it). For example, a camera application can start the activity in the email application that composes new mail, in order for the user to share a picture.

英文不太好，这里就不献丑了，这里介绍的Activity的大概意思就是说，activity在Android系统中代表的就是一个屏幕，一个App就是由许多个不同的Acitivty组成的，并且不同进程之间的Activity是可以相互调用的。

在介绍Activity的启动流程之前，我们先介绍几个概念：

Activity的生命周期

protected void onCreate(Bundle savedInstanceState);
protected void onRestart();
protected void onStart();
protected void onResume();
protected void onPause();
protected void onStop();
protected void onDestory();
以上为Activity生命周期中的各个时期的回调方法，在不同的方法中我们可以执行不同的逻辑。
关于Activity生命周期的详细介绍可以参考： Android activity的生命周期

Activity的启动模式

activity启动时可以设置不同的启动模式，主要是：standrand，singleTop，singleTask，instance等四种启动模式，不同的启动模式在启动Activity时会执行不同的逻辑，系统会按不同的启动模式将Activity存放到不同的activity栈中。
关于Activity启动模式的详细介绍，可以参考： Android任务和返回栈完全解析

Activity的启动进程

在Manifest.xml中定义Activity的时候，Activity默认是属于进程名称为包名的进程的，当然这时候是可以指定Activity的启动进程，所以在Activity启动时首先会检测当前Activity所属的进程是否已经启动，若进程没有启动，则首先会启动该进程，并在该进程启动之后才会执行Activity的启动过程。

Intent启动Activity的方式

Intent启动Activity分为两种，显示启动和隐士启动，显示启动就是在初始化Intent对象的时候直接引用需要启动的Activity的字节码，显示引用的好处就是可以直接告诉Intent对象启动的Activity对象不需要执行intent filter索引需要启动哪一个Activity，但是显示引用不能启动其他进程的Activity对象，因为无法获取其他进程的Activity对象的字节码，而隐式启动则可以通过配置Intent Filter启动其他进程的Activity对象，因此在应用内，我们一般都是使用显示启动的方式启动Activity，而如果需要启动其他应用的Activity时，一般使用隐式启动的方式。

Android基础

Android ActivityManagerNative Zygote SystemServer 安装流程

阅读更多>>

2022-08-06

2022-08-06 d455ecc084b155a6383de698ba4a457f 99+ 28 分钟 4.3 k

apk安装流程(转)

上一篇文章中给大家分析了一下android系统启动之后调用PackageManagerService服务并解析系统特定目录，解析apk文件并安装的过程，这个安装过期实际上是没有图形界面的，底层调用的是我们平时比较熟悉的adb命令，那么我们平时安装apk文件的时候大部分是都过图形界面安装的，那么这种方式安装apk具体的流程是怎样的呢？

下面我们就来具体看一下apk的具体安装过程，相信大家都知道如果我们想在代码里执行apk的安装，那么一般都是这样：

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Intent intent = new Intent(Intent.ACTION_VIEW);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.setDataAndType(Uri.parse("file://" + path),"application/vnd.android.package-archive");
context.startActivity(intent);

这样，我们就会打开安装apk文件的程序并执行安装逻辑了，那么这段代码具体是打开那个activity呢？好吧，从这个问题开始，我们来解析apk的安装流程…

这里跟大姐简单介绍一下android的源码，平时我们使用的android.jar里面的java源码只是android系统源码的一部分，还有好多源码并没有打入到android.jar中，这里为大家推荐一个android源码的地址：https://github.com/android
里面根据android系统的不同模块包含了许多android模块的源码。

这里我们找到platform_packages_apps_packageinstaller库，这里面就是android系统安装程序的源码了。

这里我们找到其androidManifest.xml，然后我们来看一下其具体的定义：

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.android.packageinstaller" coreApp="true">

<original-package android:name="com.android.packageinstaller" />

...

<application android:label="@string/app_name"
android:allowBackup="false"
android:theme="@style/Theme.DialogWhenLarge"
android:supportsRtl="true">

<activity android:name=".PackageInstallerActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:excludeFromRecents="true">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<action android:name="android.intent.action.INSTALL_PACKAGE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:scheme="file" />
<data android:mimeType="application/vnd.android.package-archive" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.INSTALL_PACKAGE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:scheme="file" />
<data android:scheme="package" />
</intent-filter>
<intent-filter>
<action android:name="android.content.pm.action.CONFIRM_PERMISSIONS" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity android:name=".InstallAppProgress"
android:configChanges="orientation|keyboardHidden|screenSize"
android:exported="false" />

<activity android:name=".UninstallerActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:excludeFromRecents="true"
android:theme="@style/Theme.AlertDialogActivity">
<intent-filter android:priority="1">
<action android:name="android.intent.action.DELETE" />
<action android:name="android.intent.action.UNINSTALL_PACKAGE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:scheme="package" />
</intent-filter>
</activity>

<activity android:name=".UninstallAppProgress"
android:configChanges="orientation|keyboardHidden|screenSize"
android:exported="false" />

<activity android:name=".permission.ui.GrantPermissionsActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:excludeFromRecents="true"
android:theme="@style/GrantPermissions">
<intent-filter>
<action android:name="android.content.pm.action.REQUEST_PERMISSIONS" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>

<activity android:name=".permission.ui.ManagePermissionsActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:excludeFromRecents="true"
android:label="@string/app_permissions"
android:theme="@style/Settings"
android:permission="android.permission.GRANT_RUNTIME_PERMISSIONS">
<intent-filter>
<action android:name="android.intent.action.MANAGE_PERMISSIONS" />
<action android:name="android.intent.action.MANAGE_APP_PERMISSIONS" />
<action android:name="android.intent.action.MANAGE_PERMISSION_APPS" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>

<activity android:name=".permission.ui.OverlayWarningDialog"
android:excludeFromRecents="true"
android:theme="@android:style/Theme.DeviceDefault.Light.Dialog.NoActionBar" />

<provider android:name=".wear.WearPackageIconProvider"
android:authorities="com.google.android.packageinstaller.wear.provider"
android:grantUriPermissions="true"
android:exported="true" />

<activity android:name=".permission.ui.wear.WarningConfirmationActivity"
android:permission="android.permission.GRANT_RUNTIME_PERMISSIONS"
android:theme="@style/Settings"/>
</application>

</manifest>

好吧，这里我们大概看一下Activity的定义，这里我们重点看一下PackageInstallerActivity的定义：

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<activity android:name=".PackageInstallerActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:excludeFromRecents="true">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<action android:name="android.intent.action.INSTALL_PACKAGE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:scheme="file" />
<data android:mimeType="application/vnd.android.package-archive" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.INSTALL_PACKAGE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:scheme="file" />
<data android:scheme="package" />
</intent-filter>
<intent-filter>
<action android:name="android.content.pm.action.CONFIRM_PERMISSIONS" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>

恩？这里不就是我们刚刚定义的启动安装Apk activity的intent filter？好吧，所以说一开始我们调用的startActivity其实启动的就是PackageInstallerActivity，那么下面我们就看一下PackageInstellerActivity的具体实现：

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@Override
protected void onCreate(Bundle icicle) {
super.onCreate(icicle);

mPm = getPackageManager();
mInstaller = mPm.getPackageInstaller();
mUserManager = (UserManager) getSystemService(Context.USER_SERVICE);

final Intent intent = getIntent();
if (PackageInstaller.ACTION_CONFIRM_PERMISSIONS.equals(intent.getAction())) {
final int sessionId = intent.getIntExtra(PackageInstaller.EXTRA_SESSION_ID, -1);
final PackageInstaller.SessionInfo info = mInstaller.getSessionInfo(sessionId);
if (info == null || !info.sealed || info.resolvedBaseCodePath == null) {
Log.w(TAG, "Session " + mSessionId + " in funky state; ignoring");
finish();
return;
}

mSessionId = sessionId;
mPackageURI = Uri.fromFile(new File(info.resolvedBaseCodePath));
mOriginatingURI = null;
mReferrerURI = null;
} else {
mSessionId = -1;
mPackageURI = intent.getData();
mOriginatingURI = intent.getParcelableExtra(Intent.EXTRA_ORIGINATING_URI);
mReferrerURI = intent.getParcelableExtra(Intent.EXTRA_REFERRER);
}

final boolean unknownSourcesAllowedByAdmin = isUnknownSourcesAllowedByAdmin();
final boolean unknownSourcesAllowedByUser = isUnknownSourcesEnabled();

boolean requestFromUnknownSource = isInstallRequestFromUnknownSource(intent);
mInstallFlowAnalytics = new InstallFlowAnalytics();
mInstallFlowAnalytics.setContext(this);
mInstallFlowAnalytics.setStartTimestampMillis(SystemClock.elapsedRealtime());
mInstallFlowAnalytics.setInstallsFromUnknownSourcesPermitted(unknownSourcesAllowedByAdmin
&& unknownSourcesAllowedByUser);
mInstallFlowAnalytics.setInstallRequestFromUnknownSource(requestFromUnknownSource);
mInstallFlowAnalytics.setVerifyAppsEnabled(isVerifyAppsEnabled());
mInstallFlowAnalytics.setAppVerifierInstalled(isAppVerifierInstalled());
mInstallFlowAnalytics.setPackageUri(mPackageURI.toString());

if (DeviceUtils.isWear(this)) {
showDialogInner(DLG_NOT_SUPPORTED_ON_WEAR);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_NOT_ALLOWED_ON_WEAR);
return;
}

final String scheme = mPackageURI.getScheme();
if (scheme != null && !"file".equals(scheme) && !"package".equals(scheme)) {
Log.w(TAG, "Unsupported scheme " + scheme);
setPmResult(PackageManager.INSTALL_FAILED_INVALID_URI);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_FAILED_UNSUPPORTED_SCHEME);
finish();
return;
}

final PackageUtil.AppSnippet as;
if ("package".equals(mPackageURI.getScheme())) {
mInstallFlowAnalytics.setFileUri(false);
try {
mPkgInfo = mPm.getPackageInfo(mPackageURI.getSchemeSpecificPart(),
PackageManager.GET_PERMISSIONS | PackageManager.GET_UNINSTALLED_PACKAGES);
} catch (NameNotFoundException e) {
}
if (mPkgInfo == null) {
Log.w(TAG, "Requested package " + mPackageURI.getScheme()
+ " not available. Discontinuing installation");
showDialogInner(DLG_PACKAGE_ERROR);
setPmResult(PackageManager.INSTALL_FAILED_INVALID_APK);
mInstallFlowAnalytics.setPackageInfoObtained();
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_FAILED_PACKAGE_MISSING);
return;
}
as = new PackageUtil.AppSnippet(mPm.getApplicationLabel(mPkgInfo.applicationInfo),
mPm.getApplicationIcon(mPkgInfo.applicationInfo));
} else {
mInstallFlowAnalytics.setFileUri(true);
final File sourceFile = new File(mPackageURI.getPath());
PackageParser.Package parsed = PackageUtil.getPackageInfo(sourceFile);

// Check for parse errors
if (parsed == null) {
Log.w(TAG, "Parse error when parsing manifest. Discontinuing installation");
showDialogInner(DLG_PACKAGE_ERROR);
setPmResult(PackageManager.INSTALL_FAILED_INVALID_APK);
mInstallFlowAnalytics.setPackageInfoObtained();
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_FAILED_TO_GET_PACKAGE_INFO);
return;
}
mPkgInfo = PackageParser.generatePackageInfo(parsed, null,
PackageManager.GET_PERMISSIONS, 0, 0, null,
new PackageUserState());
mPkgDigest = parsed.manifestDigest;
as = PackageUtil.getAppSnippet(this, mPkgInfo.applicationInfo, sourceFile);
}
mInstallFlowAnalytics.setPackageInfoObtained();

//set view
setContentView(R.layout.install_start);
mInstallConfirm = findViewById(R.id.install_confirm_panel);
mInstallConfirm.setVisibility(View.INVISIBLE);
PackageUtil.initSnippetForNewApp(this, as, R.id.app_snippet);

mOriginatingUid = getOriginatingUid(intent);

// Block the install attempt on the Unknown Sources setting if necessary.
if (!requestFromUnknownSource) {
initiateInstall();
return;
}

// If the admin prohibits it, or we're running in a managed profile, just show error
// and exit. Otherwise show an option to take the user to Settings to change the setting.
final boolean isManagedProfile = mUserManager.isManagedProfile();
if (!unknownSourcesAllowedByAdmin
|| (!unknownSourcesAllowedByUser && isManagedProfile)) {
showDialogInner(DLG_ADMIN_RESTRICTS_UNKNOWN_SOURCES);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_BLOCKED_BY_UNKNOWN_SOURCES_SETTING);
} else if (!unknownSourcesAllowedByUser) {
// Ask user to enable setting first
showDialogInner(DLG_UNKNOWN_SOURCES);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_BLOCKED_BY_UNKNOWN_SOURCES_SETTING);
} else {
initiateInstall();
}
}

这里我们主要先看一下PackageInstallerActivity的onCreate方法：

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@Override
protected void onCreate(Bundle icicle) {
super.onCreate(icicle);

mPm = getPackageManager();
mInstaller = mPm.getPackageInstaller();
mUserManager = (UserManager) getSystemService(Context.USER_SERVICE);

final Intent intent = getIntent();
if (PackageInstaller.ACTION_CONFIRM_PERMISSIONS.equals(intent.getAction())) {
final int sessionId = intent.getIntExtra(PackageInstaller.EXTRA_SESSION_ID, -1);
final PackageInstaller.SessionInfo info = mInstaller.getSessionInfo(sessionId);
if (info == null || !info.sealed || info.resolvedBaseCodePath == null) {
Log.w(TAG, "Session " + mSessionId + " in funky state; ignoring");
finish();
return;
}

mSessionId = sessionId;
mPackageURI = Uri.fromFile(new File(info.resolvedBaseCodePath));
mOriginatingURI = null;
mReferrerURI = null;
} else {
mSessionId = -1;
mPackageURI = intent.getData();
mOriginatingURI = intent.getParcelableExtra(Intent.EXTRA_ORIGINATING_URI);
mReferrerURI = intent.getParcelableExtra(Intent.EXTRA_REFERRER);
}

final boolean unknownSourcesAllowedByAdmin = isUnknownSourcesAllowedByAdmin();
final boolean unknownSourcesAllowedByUser = isUnknownSourcesEnabled();

boolean requestFromUnknownSource = isInstallRequestFromUnknownSource(intent);
mInstallFlowAnalytics = new InstallFlowAnalytics();
mInstallFlowAnalytics.setContext(this);
mInstallFlowAnalytics.setStartTimestampMillis(SystemClock.elapsedRealtime());
mInstallFlowAnalytics.setInstallsFromUnknownSourcesPermitted(unknownSourcesAllowedByAdmin
&& unknownSourcesAllowedByUser);
mInstallFlowAnalytics.setInstallRequestFromUnknownSource(requestFromUnknownSource);
mInstallFlowAnalytics.setVerifyAppsEnabled(isVerifyAppsEnabled());
mInstallFlowAnalytics.setAppVerifierInstalled(isAppVerifierInstalled());
mInstallFlowAnalytics.setPackageUri(mPackageURI.toString());

if (DeviceUtils.isWear(this)) {
showDialogInner(DLG_NOT_SUPPORTED_ON_WEAR);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_NOT_ALLOWED_ON_WEAR);
return;
}

final String scheme = mPackageURI.getScheme();
if (scheme != null && !"file".equals(scheme) && !"package".equals(scheme)) {
Log.w(TAG, "Unsupported scheme " + scheme);
setPmResult(PackageManager.INSTALL_FAILED_INVALID_URI);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_FAILED_UNSUPPORTED_SCHEME);
finish();
return;
}

final PackageUtil.AppSnippet as;
if ("package".equals(mPackageURI.getScheme())) {
mInstallFlowAnalytics.setFileUri(false);
try {
mPkgInfo = mPm.getPackageInfo(mPackageURI.getSchemeSpecificPart(),
PackageManager.GET_PERMISSIONS | PackageManager.GET_UNINSTALLED_PACKAGES);
} catch (NameNotFoundException e) {
}
if (mPkgInfo == null) {
Log.w(TAG, "Requested package " + mPackageURI.getScheme()
+ " not available. Discontinuing installation");
showDialogInner(DLG_PACKAGE_ERROR);
setPmResult(PackageManager.INSTALL_FAILED_INVALID_APK);
mInstallFlowAnalytics.setPackageInfoObtained();
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_FAILED_PACKAGE_MISSING);
return;
}
as = new PackageUtil.AppSnippet(mPm.getApplicationLabel(mPkgInfo.applicationInfo),
mPm.getApplicationIcon(mPkgInfo.applicationInfo));
} else {
mInstallFlowAnalytics.setFileUri(true);
final File sourceFile = new File(mPackageURI.getPath());
PackageParser.Package parsed = PackageUtil.getPackageInfo(sourceFile);

// Check for parse errors
if (parsed == null) {
Log.w(TAG, "Parse error when parsing manifest. Discontinuing installation");
showDialogInner(DLG_PACKAGE_ERROR);
setPmResult(PackageManager.INSTALL_FAILED_INVALID_APK);
mInstallFlowAnalytics.setPackageInfoObtained();
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_FAILED_TO_GET_PACKAGE_INFO);
return;
}
mPkgInfo = PackageParser.generatePackageInfo(parsed, null,
PackageManager.GET_PERMISSIONS, 0, 0, null,
new PackageUserState());
mPkgDigest = parsed.manifestDigest;
as = PackageUtil.getAppSnippet(this, mPkgInfo.applicationInfo, sourceFile);
}
mInstallFlowAnalytics.setPackageInfoObtained();

//set view
setContentView(R.layout.install_start);
mInstallConfirm = findViewById(R.id.install_confirm_panel);
mInstallConfirm.setVisibility(View.INVISIBLE);
PackageUtil.initSnippetForNewApp(this, as, R.id.app_snippet);

mOriginatingUid = getOriginatingUid(intent);

// Block the install attempt on the Unknown Sources setting if necessary.
if (!requestFromUnknownSource) {
initiateInstall();
return;
}

// If the admin prohibits it, or we're running in a managed profile, just show error
// and exit. Otherwise show an option to take the user to Settings to change the setting.
final boolean isManagedProfile = mUserManager.isManagedProfile();
if (!unknownSourcesAllowedByAdmin
|| (!unknownSourcesAllowedByUser && isManagedProfile)) {
showDialogInner(DLG_ADMIN_RESTRICTS_UNKNOWN_SOURCES);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_BLOCKED_BY_UNKNOWN_SOURCES_SETTING);
} else if (!unknownSourcesAllowedByUser) {
// Ask user to enable setting first
showDialogInner(DLG_UNKNOWN_SOURCES);
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_BLOCKED_BY_UNKNOWN_SOURCES_SETTING);
} else {
initiateInstall();
}
}

可以发现，在onCreate方法中，首先执行一些初始化操作，获取PackageManager和Installer、UserManager等对象，然后会根据当前Intent的信息最一些逻辑判断并弹出消息弹窗，我们可以看一下具体的消息弹窗类型：

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private static final int DLG_BASE = 0;
private static final int DLG_UNKNOWN_SOURCES = DLG_BASE + 1;
private static final int DLG_PACKAGE_ERROR = DLG_BASE + 2;
private static final int DLG_OUT_OF_SPACE = DLG_BASE + 3;
private static final int DLG_INSTALL_ERROR = DLG_BASE + 4;
private static final int DLG_ALLOW_SOURCE = DLG_BASE + 5;
private static final int DLG_ADMIN_RESTRICTS_UNKNOWN_SOURCES = DLG_BASE + 6;
private static final int DLG_NOT_SUPPORTED_ON_WEAR = DLG_BASE + 7;

可以发现当分析Intent对象的时候，如果可以得到这样几种结果：不知道apk的来源，package信息错误，存储空间不够，安装时报，来源正确，允许未知来源的apk文件，在wear上不支持等，这样根据不同的消息类型会弹出不同的消息弹窗：

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@Override
public Dialog onCreateDialog(int id, Bundle bundle) {
switch (id) {
case DLG_UNKNOWN_SOURCES:
return new AlertDialog.Builder(this)
.setTitle(R.string.unknown_apps_dlg_title)
.setMessage(R.string.unknown_apps_dlg_text)
.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
Log.i(TAG, "Finishing off activity so that user can navigate to settings manually");
finish();
}})
.setPositiveButton(R.string.settings, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
Log.i(TAG, "Launching settings");
launchSecuritySettings();
}
})
.setOnCancelListener(this)
.create();
case DLG_ADMIN_RESTRICTS_UNKNOWN_SOURCES:
return new AlertDialog.Builder(this)
.setTitle(R.string.unknown_apps_dlg_title)
.setMessage(R.string.unknown_apps_admin_dlg_text)
.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
finish();
}
})
.setOnCancelListener(this)
.create();
case DLG_PACKAGE_ERROR :
return new AlertDialog.Builder(this)
.setTitle(R.string.Parse_error_dlg_title)
.setMessage(R.string.Parse_error_dlg_text)
.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
finish();
}
})
.setOnCancelListener(this)
.create();
case DLG_OUT_OF_SPACE:
// Guaranteed not to be null. will default to package name if not set by app
CharSequence appTitle = mPm.getApplicationLabel(mPkgInfo.applicationInfo);
String dlgText = getString(R.string.out_of_space_dlg_text,
appTitle.toString());
return new AlertDialog.Builder(this)
.setTitle(R.string.out_of_space_dlg_title)
.setMessage(dlgText)
.setPositiveButton(R.string.manage_applications, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
//launch manage applications
Intent intent = new Intent("android.intent.action.MANAGE_PACKAGE_STORAGE");
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
finish();
}
})
.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
Log.i(TAG, "Canceling installation");
finish();
}
})
.setOnCancelListener(this)
.create();
case DLG_INSTALL_ERROR :
// Guaranteed not to be null. will default to package name if not set by app
CharSequence appTitle1 = mPm.getApplicationLabel(mPkgInfo.applicationInfo);
String dlgText1 = getString(R.string.install_failed_msg,
appTitle1.toString());
return new AlertDialog.Builder(this)
.setTitle(R.string.install_failed)
.setNeutralButton(R.string.ok, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
finish();
}
})
.setMessage(dlgText1)
.setOnCancelListener(this)
.create();
case DLG_ALLOW_SOURCE:
CharSequence appTitle2 = mPm.getApplicationLabel(mSourceInfo);
String dlgText2 = getString(R.string.allow_source_dlg_text,
appTitle2.toString());
return new AlertDialog.Builder(this)
.setTitle(R.string.allow_source_dlg_title)
.setMessage(dlgText2)
.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
setResult(RESULT_CANCELED);
finish();
}})
.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
SharedPreferences prefs = getSharedPreferences(PREFS_ALLOWED_SOURCES,
Context.MODE_PRIVATE);
prefs.edit().putBoolean(mSourceInfo.packageName, true).apply();
startInstallConfirm();
}
})
.setOnCancelListener(this)
.create();
case DLG_NOT_SUPPORTED_ON_WEAR:
return new AlertDialog.Builder(this)
.setTitle(R.string.wear_not_allowed_dlg_title)
.setMessage(R.string.wear_not_allowed_dlg_text)
.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
setResult(RESULT_OK);
finish();
}
})
.setOnCancelListener(this)
.create();
}
return null;
}

消息弹窗的主要作用，用于提示用户当前安装apk文件的特性。都知道android系统在android apk文件之前会解析器manifest文件，这个操作也是早onCreate方法中执行的：

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PackageParser.Package parsed = PackageUtil.getPackageInfo(sourceFile);

我们具体看一下getPackageInfo方法的实现：

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public static PackageParser.Package getPackageInfo(File sourceFile) {
final PackageParser parser = new PackageParser();
try {
PackageParser.Package pkg = parser.parseMonolithicPackage(sourceFile, 0);
parser.collectManifestDigest(pkg);
return pkg;
} catch (PackageParserException e) {
return null;
}
}

好吧，到了这里是不是代码变得很熟悉了？parseMonolithicPackage就是我们上一节分析的android系统解析manifest文件的过程，具体的可参考：http://blog.csdn.net/qq_23547831/article/details/51203482

而collectManifestDigest方法，我们这里简单的介绍一下，其主要是要争apk的签名是否正确。好吧通过这两部我们就把apk文件的manifest和签名信息都解析完成并保存在了Package中。

接着往下走，在所有的解析完成之后我们会在onCreate方法中执行initiateInstall();方法，刚方法的主要作用是初始化安装。

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private void initiateInstall() {
String pkgName = mPkgInfo.packageName;
// Check if there is already a package on the device with this name
// but it has been renamed to something else.
String[] oldName = mPm.canonicalToCurrentPackageNames(new String[] { pkgName });
if (oldName != null && oldName.length > 0 && oldName[0] != null) {
pkgName = oldName[0];
mPkgInfo.packageName = pkgName;
mPkgInfo.applicationInfo.packageName = pkgName;
}
// Check if package is already installed. display confirmation dialog if replacing pkg
try {
// This is a little convoluted because we want to get all uninstalled
// apps, but this may include apps with just data, and if it is just
// data we still want to count it as "installed".
mAppInfo = mPm.getApplicationInfo(pkgName,
PackageManager.GET_UNINSTALLED_PACKAGES);
if ((mAppInfo.flags&ApplicationInfo.FLAG_INSTALLED) == 0) {
mAppInfo = null;
}
} catch (NameNotFoundException e) {
mAppInfo = null;
}

mInstallFlowAnalytics.setReplace(mAppInfo != null);
mInstallFlowAnalytics.setSystemApp(
(mAppInfo != null) && ((mAppInfo.flags & ApplicationInfo.FLAG_SYSTEM) != 0));

// If we have a session id, we're invoked to verify the permissions for the given
// package. Otherwise, we start the install process.
if (mSessionId != -1) {
startInstallConfirm();
} else {
startInstall();
}
}

好吧，这里面有调用了startInstallConfirm方法，然后我们看一下startInstallConfirm方法的实现:

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private void startInstallConfirm() {
...
//初始化安装确认界面
...
}

好吧，这个方法的实现比较简单，主要的实现逻辑就是现实该activity的用户界面，平时我们安装某一个应用的时候会弹出一个安装确认页面，还有一个确认和取消按钮，有印象么？其实就是在这里执行的界面初始化操作。

好吧，一般情况下在apk安装确认页面，我们会点击确认按钮执行安装逻辑吧？那么这里我们找一下确认按钮的点击事件：

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public void onClick(View v) {
if (v == mOk) {
if (mOkCanInstall || mScrollView == null) {
mInstallFlowAnalytics.setInstallButtonClicked();
if (mSessionId != -1) {
mInstaller.setPermissionsResult(mSessionId, true);

// We're only confirming permissions, so we don't really know how the
// story ends; assume success.
mInstallFlowAnalytics.setFlowFinishedWithPackageManagerResult(
PackageManager.INSTALL_SUCCEEDED);
finish();
} else {
startInstall();
}
} else {
mScrollView.pageScroll(View.FOCUS_DOWN);
}
} else if (v == mCancel) {
// Cancel and finish
setResult(RESULT_CANCELED);
if (mSessionId != -1) {
mInstaller.setPermissionsResult(mSessionId, false);
}
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_CANCELLED_BY_USER);
finish();
}
}

很明显了，这里当我们点击确认按钮的时候会执行startInstall方法，也就是开始执行安装逻辑：

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private void startInstall() {
// Start subactivity to actually install the application
Intent newIntent = new Intent();
newIntent.putExtra(PackageUtil.INTENT_ATTR_APPLICATION_INFO,
mPkgInfo.applicationInfo);
newIntent.setData(mPackageURI);
newIntent.setClass(this, InstallAppProgress.class);
newIntent.putExtra(InstallAppProgress.EXTRA_MANIFEST_DIGEST, mPkgDigest);
newIntent.putExtra(
InstallAppProgress.EXTRA_INSTALL_FLOW_ANALYTICS, mInstallFlowAnalytics);
String installerPackageName = getIntent().getStringExtra(
Intent.EXTRA_INSTALLER_PACKAGE_NAME);
if (mOriginatingURI != null) {
newIntent.putExtra(Intent.EXTRA_ORIGINATING_URI, mOriginatingURI);
}
if (mReferrerURI != null) {
newIntent.putExtra(Intent.EXTRA_REFERRER, mReferrerURI);
}
if (mOriginatingUid != VerificationParams.NO_UID) {
newIntent.putExtra(Intent.EXTRA_ORIGINATING_UID, mOriginatingUid);
}
if (installerPackageName != null) {
newIntent.putExtra(Intent.EXTRA_INSTALLER_PACKAGE_NAME,
installerPackageName);
}
if (getIntent().getBooleanExtra(Intent.EXTRA_RETURN_RESULT, false)) {
newIntent.putExtra(Intent.EXTRA_RETURN_RESULT, true);
newIntent.addFlags(Intent.FLAG_ACTIVITY_FORWARD_RESULT);
}
if(localLOGV) Log.i(TAG, "downloaded app uri="+mPackageURI);
startActivity(newIntent);
finish();
}

可以发现，点击确认按钮之后我们调用启用了一个新的Activity–>InstallAppProgress，这个Activity主要用于执行apk的安装逻辑了。

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@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
Intent intent = getIntent();
mAppInfo = intent.getParcelableExtra(PackageUtil.INTENT_ATTR_APPLICATION_INFO);
mInstallFlowAnalytics = intent.getParcelableExtra(EXTRA_INSTALL_FLOW_ANALYTICS);
mInstallFlowAnalytics.setContext(this);
mPackageURI = intent.getData();

final String scheme = mPackageURI.getScheme();
if (scheme != null && !"file".equals(scheme) && !"package".equals(scheme)) {
mInstallFlowAnalytics.setFlowFinished(
InstallFlowAnalytics.RESULT_FAILED_UNSUPPORTED_SCHEME);
throw new IllegalArgumentException("unexpected scheme " + scheme);
}

mInstallThread = new HandlerThread("InstallThread");
mInstallThread.start();
mInstallHandler = new Handler(mInstallThread.getLooper());

IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction(BROADCAST_ACTION);
registerReceiver(
mBroadcastReceiver, intentFilter, BROADCAST_SENDER_PERMISSION, null /*scheduler*/);

initView();
}

可以发现InstallAppProcess这个Activity的onCreate方法中主要初始化了一些成员变量，并调用initView方法，我们在iniTView方法中可以看到：

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void initView() {
...
mInstallHandler.post(new Runnable() {
@Override
public void run() {
doPackageStage(pm, params);
}
});
...
}

经过一些view的初始化操作之后调用了doPackageStage方法，该方法主要是通过调用PackageInstaller执行apk文件的安装，这里就不在详细的介绍了，在apk文件安装完成之后PackageInstaller会发送一个安装完成的广播，刚刚我们在onCreate方法中注册了一个广播接收器，其可以用来接收apk安装完成的广播：

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private final BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final int statusCode = intent.getIntExtra(
PackageInstaller.EXTRA_STATUS, PackageInstaller.STATUS_FAILURE);
if (statusCode == PackageInstaller.STATUS_PENDING_USER_ACTION) {
context.startActivity((Intent)intent.getParcelableExtra(Intent.EXTRA_INTENT));
} else {
onPackageInstalled(statusCode);
}
}
};

这样apk安装完成之后，这里的广播接收器会接收到广播并执行onPackageInstalled方法，执行后续的处理逻辑，那么我们来看一下onPackageInstalled方法的具体实现逻辑：

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void onPackageInstalled(int statusCode) {
Message msg = mHandler.obtainMessage(INSTALL_COMPLETE);
msg.arg1 = statusCode;
mHandler.sendMessage(msg);
}

好吧，这里是发送Handler异步消息，我们来看一下异步消息的处理逻辑：

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private Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
switch (msg.what) {
case INSTALL_COMPLETE:
mInstallFlowAnalytics.setFlowFinishedWithPackageManagerResult(msg.arg1);
if (getIntent().getBooleanExtra(Intent.EXTRA_RETURN_RESULT, false)) {
Intent result = new Intent();
result.putExtra(Intent.EXTRA_INSTALL_RESULT, msg.arg1);
setResult(msg.arg1 == PackageInstaller.STATUS_SUCCESS
? Activity.RESULT_OK : Activity.RESULT_FIRST_USER,
result);
finish();
return;
}
// Update the status text
mProgressBar.setVisibility(View.INVISIBLE);
// Show the ok button
int centerTextLabel;
int centerExplanationLabel = -1;
LevelListDrawable centerTextDrawable =
(LevelListDrawable) getDrawable(R.drawable.ic_result_status);
if (msg.arg1 == PackageInstaller.STATUS_SUCCESS) {
mLaunchButton.setVisibility(View.VISIBLE);
centerTextDrawable.setLevel(0);
centerTextLabel = R.string.install_done;
// Enable or disable launch button
mLaunchIntent = getPackageManager().getLaunchIntentForPackage(
mAppInfo.packageName);
boolean enabled = false;
if(mLaunchIntent != null) {
List<ResolveInfo> list = getPackageManager().
queryIntentActivities(mLaunchIntent, 0);
if (list != null && list.size() > 0) {
enabled = true;
}
}
if (enabled) {
mLaunchButton.setOnClickListener(InstallAppProgress.this);
} else {
mLaunchButton.setEnabled(false);
}
} else if (msg.arg1 == PackageInstaller.STATUS_FAILURE_STORAGE){
showDialogInner(DLG_OUT_OF_SPACE);
return;
} else {
// Generic error handling for all other error codes.
centerTextDrawable.setLevel(1);
centerExplanationLabel = getExplanationFromErrorCode(msg.arg1);
centerTextLabel = R.string.install_failed;
mLaunchButton.setVisibility(View.INVISIBLE);
}
if (centerTextDrawable != null) {
centerTextDrawable.setBounds(0, 0,
centerTextDrawable.getIntrinsicWidth(),
centerTextDrawable.getIntrinsicHeight());
mStatusTextView.setCompoundDrawablesRelative(centerTextDrawable, null,
null, null);
}
mStatusTextView.setText(centerTextLabel);
if (centerExplanationLabel != -1) {
mExplanationTextView.setText(centerExplanationLabel);
mExplanationTextView.setVisibility(View.VISIBLE);
} else {
mExplanationTextView.setVisibility(View.GONE);
}
mDoneButton.setOnClickListener(InstallAppProgress.this);
mOkPanel.setVisibility(View.VISIBLE);
break;
default:
break;
}
}
};

可以发现，当apk安装完成之后，我们会更新UI，显示完成和打开按钮，是不是和我们平时安装apk的逻辑对应上了？这时候我们可以看一下这两个按钮的点击事件。

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public void onClick(View v) {
if(v == mDoneButton) {
if (mAppInfo.packageName != null) {
Log.i(TAG, "Finished installing "+mAppInfo.packageName);
}
finish();
} else if(v == mLaunchButton) {
startActivity(mLaunchIntent);
finish();
}
}

好吧，比较简单，点击完成按钮，直接finish掉这个activity，点击打开，则直接调用startActivity启动安装的应用，然后直接finish自身。

总结：

代码中执行intent.setDataAndType(Uri.parse(“file://“ + path),”application/vnd.android.package-archive”);可以调起PackageInstallerActivity；

PackageInstallerActivity主要用于执行解析apk文件，解析manifest，解析签名等操作；

InstallAppProcess主要用于执行安装apk逻辑，用于初始化安装界面，用于初始化用户UI。并调用PackageInstaller执行安装逻辑；

InstallAppProcess内注册有广播，当安装完成之后接收广播，更新UI。显示apk安装完成界面；

另外对android源码解析方法感兴趣的可参考我的：

android源码解析之（一）–>android项目构建过程

 android源码解析之（二）–>异步消息机制

 android源码解析之（三）–>异步任务AsyncTask

android源码解析之（四）–>HandlerThread

android源码解析之（五）–>IntentService

android源码解析之（六）–>Log

android源码解析之（七）–>LruCache

android源码解析之（八）–>Zygote进程启动流程

 android源码解析之（九）–>SystemServer进程启动流程

 android源码解析之（十）–>Launcher启动流程

 android源码解析之（十一）–>应用进程启动流程

 android源码解析之（十二）–>系统启动并解析Manifest的流程

Android基础

Android Zygote SystemServer 安装流程 PackageManagerService

2022-08-06 d872f01429a96389145ed69ee908b1c9 99+ 29 分钟 4.3 k

系统启动并解析Manifest的流程(转)

最近有同学问我关于Manifest何时被系统解析的问题，正好也分析到这一块了，索性这一章就讲解一下android系统何时解析Manifest吧，这里的Manifest指的是android安装文件apk中的androidManifest.xml文件是何时被解析的。
大家应该都知道，Android系统启动之后，我们就可以在一个应用中打开另一个从未打开过的应用，或者是在一个应用中发送广播，如果另外一个应用设置了这个广播的接收器，那么这个应用进程就会被启动并接收该广播并作出相应的处理，这样的例子很多，我们可以猜测到Android系统在启动的时候就会抓取到了系统中所有安装的应用信息（应该是解析apk文件的Manifest信息），即在Android系统的启动过程中就已经解析了系统中安装应用的androidManifest.xml文件并保存起来了，那么这个过程具体是如何的呢?

其实android系统启动过程中解析Manifest的流程是通过PackageManagerService服务来实现的。这里我们重点分析一下PackageManagerService服务是如何解析Manifest的。

首先看一下在SystemServer进程启动过程中是如何启动PackageManagerService服务的：

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private void startBootstrapServices() {
...
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();

...
}

在SystemServer进程启动过程中会调用SystemServer类的startBootstrapServices方法（主要用于启动ActivityManagerService服务和PackageManagerService服务），然后会在这个方法中会调用PackageManagerService.main静态方法，这个方法主要是用来初始化PackageManagerService服务并执行相关逻辑的。下面我来看一下main方法的具体逻辑：

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public static PackageManagerService main(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
PackageManagerService m = new PackageManagerService(context, installer,
factoryTest, onlyCore);
ServiceManager.addService("package", m);
return m;
}

可以发现main方法的实现逻辑主要是创建了一个PackageManagerService对象，并将这个对象添加到ServierManager中为其他组件提供服务。好吧，看来PackageManagerService的初始化操作主要是在PackageManagerService的构造方法中了，下面我们来看一下其构造方法的实现逻辑：

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File dataDir = Environment.getDataDirectory();
mAppDataDir = new File(dataDir, "data");
mAppInstallDir = new File(dataDir, "app");
mAppLib32InstallDir = new File(dataDir, "app-lib");
mAsecInternalPath = new File(dataDir, "app-asec").getPath();
mUserAppDataDir = new File(dataDir, "user");
mDrmAppPrivateInstallDir = new File(dataDir, "app-private");

PackageManagerService的构造方法代码量比较大，这里就不贴出所有的代码了，我们主要和解析Manifest相关的主要代码，在构造方法中有这样几段代码。可以发现在构造方法中，解析了系统中几个apk的安装目录，这几个目录就是系统中安装apk的目录，android系统会默认解析这几个目录下apk文件，也就是说如果我们android手机在其他的目录下存在apk文件系统是不会默认解析的，反过来说，如果我们把我们的apk文件移动到这几个目录下，那么重新启动操作系统，该apk文件就会被系统解析并执行相关的逻辑操作，具体做什么操作呢？我们看下面的实现。

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/ overlay packages if they reside in VENDOR_OVERLAY_DIR.
File vendorOverlayDir = new File(VENDOR_OVERLAY_DIR);
scanDirLI(vendorOverlayDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags | SCAN_TRUSTED_OVERLAY, 0);

// Find base frameworks (resource packages without code).
scanDirLI(frameworkDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR
| PackageParser.PARSE_IS_PRIVILEGED,
scanFlags | SCAN_NO_DEX, 0);

// Collected privileged system packages.
final File privilegedAppDir = new File(Environment.getRootDirectory(), "priv-app");
scanDirLI(privilegedAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR
| PackageParser.PARSE_IS_PRIVILEGED, scanFlags, 0);

// Collect ordinary system packages.
final File systemAppDir = new File(Environment.getRootDirectory(), "app");
scanDirLI(systemAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);

// Collect all vendor packages.
File vendorAppDir = new File("/vendor/app");
try {
vendorAppDir = vendorAppDir.getCanonicalFile();
} catch (IOException e) {
// failed to look up canonical path, continue with original one
}
scanDirLI(vendorAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);

// Collect all OEM packages.
final File oemAppDir = new File(Environment.getOemDirectory(), "app");
scanDirLI(oemAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);

在我们刚刚的PackageManagerService.mani方法中，解析完刚刚的几个系统目录之后系统会调用scanDirLI方法，那么这个方法主要是做什么用的呢？看它的名字应该是遍历这个系统目录。好吧，这个方法主要就是用于解析上面几个目录下的apk文件的。不信？我们看一下scanDirLI方法的具体实现：

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private void scanDirLI(File dir, int parseFlags, int scanFlags, long currentTime) {
final File[] files = dir.listFiles();
if (ArrayUtils.isEmpty(files)) {
Log.d(TAG, "No files in app dir " + dir);
return;
}

if (DEBUG_PACKAGE_SCANNING) {
Log.d(TAG, "Scanning app dir " + dir + " scanFlags=" + scanFlags
+ " flags=0x" + Integer.toHexString(parseFlags));
}

for (File file : files) {
final boolean isPackage = (isApkFile(file) || file.isDirectory())
&& !PackageInstallerService.isStageName(file.getName());
if (!isPackage) {
// Ignore entries which are not packages
continue;
}
try {
scanPackageLI(file, parseFlags | PackageParser.PARSE_MUST_BE_APK,
scanFlags, currentTime, null);
} catch (PackageManagerException e) {
Slog.w(TAG, "Failed to parse " + file + ": " + e.getMessage());

// Delete invalid userdata apps
if ((parseFlags & PackageParser.PARSE_IS_SYSTEM) == 0 &&
e.error == PackageManager.INSTALL_FAILED_INVALID_APK) {
logCriticalInfo(Log.WARN, "Deleting invalid package at " + file);
if (file.isDirectory()) {
mInstaller.rmPackageDir(file.getAbsolutePath());
} else {
file.delete();
}
}
}
}
}

可以放下其首先会遍历该目录下的所有文件，并判断是否是apk文件，如果是apk文件则调用scanPackageLI方法，scanPackageLI方法的名字很明显，就是用于解析这个apk文件的。

继续看一下scanPakcageLI方法的实现：

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private PackageParser.Package scanPackageLI(File scanFile, int parseFlags, int scanFlags,
long currentTime, UserHandle user) throws PackageManagerException {
if (DEBUG_INSTALL) Slog.d(TAG, "Parsing: " + scanFile);
parseFlags |= mDefParseFlags;
PackageParser pp = new PackageParser();
pp.setSeparateProcesses(mSeparateProcesses);
pp.setOnlyCoreApps(mOnlyCore);
pp.setDisplayMetrics(mMetrics);

if ((scanFlags & SCAN_TRUSTED_OVERLAY) != 0) {
parseFlags |= PackageParser.PARSE_TRUSTED_OVERLAY;
}

final PackageParser.Package pkg;
try {
pkg = pp.parsePackage(scanFile, parseFlags);
} catch (PackageParserException e) {
throw PackageManagerException.from(e);
}
...
}

好吧，这个方法也比较复杂，这里只是列出重点相关的代码，我们可以发现在这个方法中创建了一个PackagerParser对象，并调用了parsePackage方法，这个方法其实就是解析Manifest的主要方法，我们可以看一下其具体的实现：

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public Package parsePackage(File packageFile, int flags) throws PackageParserException {
if (packageFile.isDirectory()) {
return parseClusterPackage(packageFile, flags);
} else {
return parseMonolithicPackage(packageFile, flags);
}
}

可以发现，若我们解析的File对象是一个文件夹则执行调用parseClusterPackage方法，否则调用执行parseMonolithicPackage方法，很明显的因为我们这里解析的是apk文件（在上一方法中我们循环遍历得到了apk文件，这里的File对象就代表了一个个的apk文件信息），所以这里会执行parseMonolithicPackage方法，然后我们来看一下parseMonolithicPackage方法：

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public Package parseMonolithicPackage(File apkFile, int flags) throws PackageParserException {
if (mOnlyCoreApps) {
final PackageLite lite = parseMonolithicPackageLite(apkFile, flags);
if (!lite.coreApp) {
throw new PackageParserException(INSTALL_PARSE_FAILED_MANIFEST_MALFORMED,
"Not a coreApp: " + apkFile);
}
}

final AssetManager assets = new AssetManager();
try {
final Package pkg = parseBaseApk(apkFile, assets, flags);
pkg.codePath = apkFile.getAbsolutePath();
return pkg;
} finally {
IoUtils.closeQuietly(assets);
}
}

可以看出，这里又调用了parseBaseApk方法：

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private Package parseBaseApk(File apkFile, AssetManager assets, int flags)
...
final Package pkg = parseBaseApk(res, parser, flags, outError);
...
}

可以看出，这个parseBaseApk方法调用了其重载的parseBaseApk方法：

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while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}

String tagName = parser.getName();
if (tagName.equals("application")) {
if (foundApp) {
if (RIGID_PARSER) {
outError[0] = "<manifest> has more than one <application>";
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;
} else {
Slog.w(TAG, "<manifest> has more than one <application>");
XmlUtils.skipCurrentTag(parser);
continue;
}
}

foundApp = true;
if (!parseBaseApplication(pkg, res, parser, attrs, flags, outError)) {
return null;
}
} else if (tagName.equals("overlay")) {
pkg.mTrustedOverlay = trustedOverlay;

sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestResourceOverlay);
pkg.mOverlayTarget = sa.getString(
com.android.internal.R.styleable.AndroidManifestResourceOverlay_targetPackage);
pkg.mOverlayPriority = sa.getInt(
com.android.internal.R.styleable.AndroidManifestResourceOverlay_priority,
-1);
sa.recycle();

if (pkg.mOverlayTarget == null) {
outError[0] = "<overlay> does not specify a target package";
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;
}
if (pkg.mOverlayPriority < 0 || pkg.mOverlayPriority > 9999) {
outError[0] = "<overlay> priority must be between 0 and 9999";
mParseError =
PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;
}
XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("key-sets")) {
if (!parseKeySets(pkg, res, parser, attrs, outError)) {
return null;
}
} else if (tagName.equals("permission-group")) {
if (parsePermissionGroup(pkg, flags, res, parser, attrs, outError) == null) {
return null;
}
} else if (tagName.equals("permission")) {
if (parsePermission(pkg, res, parser, attrs, outError) == null) {
return null;
}
} else if (tagName.equals("permission-tree")) {
if (parsePermissionTree(pkg, res, parser, attrs, outError) == null) {
return null;
}
} else if (tagName.equals("uses-permission")) {
if (!parseUsesPermission(pkg, res, parser, attrs)) {
return null;
}
} else if (tagName.equals("uses-permission-sdk-m")
|| tagName.equals("uses-permission-sdk-23")) {
if (!parseUsesPermission(pkg, res, parser, attrs)) {
return null;
}
} else if (tagName.equals("uses-configuration")) {
ConfigurationInfo cPref = new ConfigurationInfo();
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestUsesConfiguration);
cPref.reqTouchScreen = sa.getInt(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqTouchScreen,
Configuration.TOUCHSCREEN_UNDEFINED);
cPref.reqKeyboardType = sa.getInt(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqKeyboardType,
Configuration.KEYBOARD_UNDEFINED);
if (sa.getBoolean(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqHardKeyboard,
false)) {
cPref.reqInputFeatures |= ConfigurationInfo.INPUT_FEATURE_HARD_KEYBOARD;
}
cPref.reqNavigation = sa.getInt(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqNavigation,
Configuration.NAVIGATION_UNDEFINED);
if (sa.getBoolean(
com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqFiveWayNav,
false)) {
cPref.reqInputFeatures |= ConfigurationInfo.INPUT_FEATURE_FIVE_WAY_NAV;
}
sa.recycle();
pkg.configPreferences = ArrayUtils.add(pkg.configPreferences, cPref);

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("uses-feature")) {
FeatureInfo fi = parseUsesFeature(res, attrs);
pkg.reqFeatures = ArrayUtils.add(pkg.reqFeatures, fi);

if (fi.name == null) {
ConfigurationInfo cPref = new ConfigurationInfo();
cPref.reqGlEsVersion = fi.reqGlEsVersion;
pkg.configPreferences = ArrayUtils.add(pkg.configPreferences, cPref);
}

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("feature-group")) {
FeatureGroupInfo group = new FeatureGroupInfo();
ArrayList<FeatureInfo> features = null;
final int innerDepth = parser.getDepth();
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > innerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}

final String innerTagName = parser.getName();
if (innerTagName.equals("uses-feature")) {
FeatureInfo featureInfo = parseUsesFeature(res, attrs);
// FeatureGroups are stricter and mandate that
// any <uses-feature> declared are mandatory.
featureInfo.flags |= FeatureInfo.FLAG_REQUIRED;
features = ArrayUtils.add(features, featureInfo);
} else {
Slog.w(TAG, "Unknown element under <feature-group>: " + innerTagName +
" at " + mArchiveSourcePath + " " +
parser.getPositionDescription());
}
XmlUtils.skipCurrentTag(parser);
}

if (features != null) {
group.features = new FeatureInfo[features.size()];
group.features = features.toArray(group.features);
}
pkg.featureGroups = ArrayUtils.add(pkg.featureGroups, group);

} else if (tagName.equals("uses-sdk")) {
if (SDK_VERSION > 0) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestUsesSdk);

int minVers = 0;
String minCode = null;
int targetVers = 0;
String targetCode = null;

TypedValue val = sa.peekValue(
com.android.internal.R.styleable.AndroidManifestUsesSdk_minSdkVersion);
if (val != null) {
if (val.type == TypedValue.TYPE_STRING && val.string != null) {
targetCode = minCode = val.string.toString();
} else {
// If it's not a string, it's an integer.
targetVers = minVers = val.data;
}
}

val = sa.peekValue(
com.android.internal.R.styleable.AndroidManifestUsesSdk_targetSdkVersion);
if (val != null) {
if (val.type == TypedValue.TYPE_STRING && val.string != null) {
targetCode = minCode = val.string.toString();
} else {
// If it's not a string, it's an integer.
targetVers = val.data;
}
}

sa.recycle();

if (minCode != null) {
boolean allowedCodename = false;
for (String codename : SDK_CODENAMES) {
if (minCode.equals(codename)) {
allowedCodename = true;
break;
}
}
if (!allowedCodename) {
if (SDK_CODENAMES.length > 0) {
outError[0] = "Requires development platform " + minCode
+ " (current platform is any of "
+ Arrays.toString(SDK_CODENAMES) + ")";
} else {
outError[0] = "Requires development platform " + minCode
+ " but this is a release platform.";
}
mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
return null;
}
} else if (minVers > SDK_VERSION) {
outError[0] = "Requires newer sdk version #" + minVers
+ " (current version is #" + SDK_VERSION + ")";
mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
return null;
}

if (targetCode != null) {
boolean allowedCodename = false;
for (String codename : SDK_CODENAMES) {
if (targetCode.equals(codename)) {
allowedCodename = true;
break;
}
}
if (!allowedCodename) {
if (SDK_CODENAMES.length > 0) {
outError[0] = "Requires development platform " + targetCode
+ " (current platform is any of "
+ Arrays.toString(SDK_CODENAMES) + ")";
} else {
outError[0] = "Requires development platform " + targetCode
+ " but this is a release platform.";
}
mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
return null;
}
// If the code matches, it definitely targets this SDK.
pkg.applicationInfo.targetSdkVersion
= android.os.Build.VERSION_CODES.CUR_DEVELOPMENT;
} else {
pkg.applicationInfo.targetSdkVersion = targetVers;
}
}

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("supports-screens")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestSupportsScreens);

pkg.applicationInfo.requiresSmallestWidthDp = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_requiresSmallestWidthDp,
0);
pkg.applicationInfo.compatibleWidthLimitDp = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_compatibleWidthLimitDp,
0);
pkg.applicationInfo.largestWidthLimitDp = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_largestWidthLimitDp,
0);

// This is a trick to get a boolean and still able to detect
// if a value was actually set.
supportsSmallScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_smallScreens,
supportsSmallScreens);
supportsNormalScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_normalScreens,
supportsNormalScreens);
supportsLargeScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_largeScreens,
supportsLargeScreens);
supportsXLargeScreens = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_xlargeScreens,
supportsXLargeScreens);
resizeable = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_resizeable,
resizeable);
anyDensity = sa.getInteger(
com.android.internal.R.styleable.AndroidManifestSupportsScreens_anyDensity,
anyDensity);

sa.recycle();

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("protected-broadcast")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestProtectedBroadcast);

// Note: don't allow this value to be a reference to a resource
// that may change.
String name = sa.getNonResourceString(
com.android.internal.R.styleable.AndroidManifestProtectedBroadcast_name);

sa.recycle();

if (name != null && (flags&PARSE_IS_SYSTEM) != 0) {
if (pkg.protectedBroadcasts == null) {
pkg.protectedBroadcasts = new ArrayList<String>();
}
if (!pkg.protectedBroadcasts.contains(name)) {
pkg.protectedBroadcasts.add(name.intern());
}
}

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("instrumentation")) {
if (parseInstrumentation(pkg, res, parser, attrs, outError) == null) {
return null;
}

} else if (tagName.equals("original-package")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestOriginalPackage);

String orig =sa.getNonConfigurationString(
com.android.internal.R.styleable.AndroidManifestOriginalPackage_name, 0);
if (!pkg.packageName.equals(orig)) {
if (pkg.mOriginalPackages == null) {
pkg.mOriginalPackages = new ArrayList<String>();
pkg.mRealPackage = pkg.packageName;
}
pkg.mOriginalPackages.add(orig);
}

sa.recycle();

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("adopt-permissions")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestOriginalPackage);

String name = sa.getNonConfigurationString(
com.android.internal.R.styleable.AndroidManifestOriginalPackage_name, 0);

sa.recycle();

if (name != null) {
if (pkg.mAdoptPermissions == null) {
pkg.mAdoptPermissions = new ArrayList<String>();
}
pkg.mAdoptPermissions.add(name);
}

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("uses-gl-texture")) {
// Just skip this tag
XmlUtils.skipCurrentTag(parser);
continue;

} else if (tagName.equals("compatible-screens")) {
// Just skip this tag
XmlUtils.skipCurrentTag(parser);
continue;
} else if (tagName.equals("supports-input")) {
XmlUtils.skipCurrentTag(parser);
continue;

} else if (tagName.equals("eat-comment")) {
// Just skip this tag
XmlUtils.skipCurrentTag(parser);
continue;

} else if (RIGID_PARSER) {
outError[0] = "Bad element under <manifest>: "
+ parser.getName();
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return null;

} else {
Slog.w(TAG, "Unknown element under <manifest>: " + parser.getName()
+ " at " + mArchiveSourcePath + " "
+ parser.getPositionDescription());
XmlUtils.skipCurrentTag(parser);
continue;
}
}

在这个parseBaseApk方法中有一个while循环，该循环主要就是用于解析AndroidManifest.xml文件中的节点信息。在开始解析application节点的时候，同时调用了parseBaseApplication方法，该方法解析了application节点下的activity，service，broadcast，contentprovier等组件的定义信息：

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while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > innerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}

String tagName = parser.getName();
if (tagName.equals("activity")) {
Activity a = parseActivity(owner, res, parser, attrs, flags, outError, false,
owner.baseHardwareAccelerated);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}

owner.activities.add(a);

} else if (tagName.equals("receiver")) {
Activity a = parseActivity(owner, res, parser, attrs, flags, outError, true, false);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}

owner.receivers.add(a);

} else if (tagName.equals("service")) {
Service s = parseService(owner, res, parser, attrs, flags, outError);
if (s == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}

owner.services.add(s);

} else if (tagName.equals("provider")) {
Provider p = parseProvider(owner, res, parser, attrs, flags, outError);
if (p == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}

owner.providers.add(p);

} else if (tagName.equals("activity-alias")) {
Activity a = parseActivityAlias(owner, res, parser, attrs, flags, outError);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}

owner.activities.add(a);

} else if (parser.getName().equals("meta-data")) {
// note: application meta-data is stored off to the side, so it can
// remain null in the primary copy (we like to avoid extra copies because
// it can be large)
if ((owner.mAppMetaData = parseMetaData(res, parser, attrs, owner.mAppMetaData,
outError)) == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}

} else if (tagName.equals("library")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestLibrary);

// Note: don't allow this value to be a reference to a resource
// that may change.
String lname = sa.getNonResourceString(
com.android.internal.R.styleable.AndroidManifestLibrary_name);

sa.recycle();

if (lname != null) {
lname = lname.intern();
if (!ArrayUtils.contains(owner.libraryNames, lname)) {
owner.libraryNames = ArrayUtils.add(owner.libraryNames, lname);
}
}

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("uses-library")) {
sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestUsesLibrary);

// Note: don't allow this value to be a reference to a resource
// that may change.
String lname = sa.getNonResourceString(
com.android.internal.R.styleable.AndroidManifestUsesLibrary_name);
boolean req = sa.getBoolean(
com.android.internal.R.styleable.AndroidManifestUsesLibrary_required,
true);

sa.recycle();

if (lname != null) {
lname = lname.intern();
if (req) {
owner.usesLibraries = ArrayUtils.add(owner.usesLibraries, lname);
} else {
owner.usesOptionalLibraries = ArrayUtils.add(
owner.usesOptionalLibraries, lname);
}
}

XmlUtils.skipCurrentTag(parser);

} else if (tagName.equals("uses-package")) {
// Dependencies for app installers; we don't currently try to
// enforce this.
XmlUtils.skipCurrentTag(parser);

} else {
if (!RIGID_PARSER) {
Slog.w(TAG, "Unknown element under <application>: " + tagName
+ " at " + mArchiveSourcePath + " "
+ parser.getPositionDescription());
XmlUtils.skipCurrentTag(parser);
continue;
} else {
outError[0] = "Bad element under <application>: " + tagName;
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
}
}

这样，经过这里循环遍历，整个androidManifest的节点信息就被解析并保存在了Package对象中。可以看到我们平时在Manifest中定义的各种节点，其实都是在这里有所体现。当androidManifest.xml文件被解析完成之后会调用我们刚刚介绍的scanPackageLI的重载方法，将解析完成的Package对象信息保存的Setting对象中，这个对象用于保存app的安装信息，具体实现是在方法：

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private PackageParser.Package scanPackageLI(File scanFile, int parseFlags, int scanFlags,
long currentTime, UserHandle user) throws PackageManagerException

当解析完成manifest文件之后会调用其重载方法：

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// Note that we invoke the following method only if we are about to unpack an application
PackageParser.Package scannedPkg = scanPackageLI(pkg, parseFlags, scanFlags
| SCAN_UPDATE_SIGNATURE, currentTime, user);

这样，解析的manifest文件信息就会被保存到Settings中，并持久化，然后执行安装apk的操作，我们可以看一下该重载方法的具体实现：

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private PackageParser.Package scanPackageLI(PackageParser.Package pkg, int parseFlags,
int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
boolean success = false;
try {
final PackageParser.Package res = scanPackageDirtyLI(pkg, parseFlags, scanFlags,
currentTime, user);
success = true;
return res;
} finally {
if (!success && (scanFlags & SCAN_DELETE_DATA_ON_FAILURES) != 0) {
removeDataDirsLI(pkg.volumeUuid, pkg.packageName);
}
}
}

可以发现其内部调用了scanPackageDirtyLI方法，这个方法就是实际实现持久化manifest信息并安装APK操作的：

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private PackageParser.Package scanPackageDirtyLI(PackageParser.Package pkg, int parseFlags,
int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
...
// And now re-install the app.
ret = createDataDirsLI(pkg.volumeUuid, pkgName, pkg.applicationInfo.uid,
pkg.applicationInfo.seinfo);
...
}

可以发现其内部调用了createDataDirLI，该方法主要实现安装apk的操作。

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private int createDataDirsLI(String volumeUuid, String packageName, int uid, String seinfo) {
int[] users = sUserManager.getUserIds();
int res = mInstaller.install(volumeUuid, packageName, uid, uid, seinfo);
if (res < 0) {
return res;
}
for (int user : users) {
if (user != 0) {
res = mInstaller.createUserData(volumeUuid, packageName,
UserHandle.getUid(user, uid), user, seinfo);
if (res < 0) {
return res;
}
}
}
return res;
}

查看该方法的实现：

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public int install(String uuid, String name, int uid, int gid, String seinfo) {
StringBuilder builder = new StringBuilder("install");
builder.append(' ');
builder.append(escapeNull(uuid));
builder.append(' ');
builder.append(name);
builder.append(' ');
builder.append(uid);
builder.append(' ');
builder.append(gid);
builder.append(' ');
builder.append(seinfo != null ? seinfo : "!");
return mInstaller.execute(builder.toString());
}

怎么样？很熟悉吧，这里的Installer其实调用的就是我们平时运行android项目很熟悉的install命令，原来android系统安装apk文件底层都是调用的adb命令。

总结：

android系统启动之后会解析固定目录下的apk文件，并执行解析，持久化apk信息，重新安装等操作；

解析Manifest流程：Zygote进程 –> SystemServer进程 –> PackgeManagerService服务 –> scanDirLI方法 –> scanPackageLI方法 –> PackageParser.parserPackage方法；

解析完成Manifest之后会将apk的Manifest信息保存在Settings对象中并持久化，然后执行重新安装的操作；

另外对android源码解析方法感兴趣的可参考我的：

android源码解析之（一）–>android项目构建过程

 android源码解析之（二）–>异步消息机制

 android源码解析之（三）–>异步任务AsyncTask

android源码解析之（四）–>HandlerThread

android源码解析之（五）–>IntentService

android源码解析之（六）–>Log

android源码解析之（七）–>LruCache

android源码解析之（八）–>Zygote进程启动流程

 android源码解析之（九）–>SystemServer进程启动流程

 android源码解析之（十）–>Launcher启动流程

 android源码解析之（十一）–>应用进程启动流程

Android基础

Android Zygote SystemServer PackageManagerService Manifest

2022-08-06 895d5d89f4a9cef76e649780a6539152 99+ 17 分钟 2.5 k

应用进程启动流程(转)

转载请标明出处：一片枫叶的专栏

在android guide中有这样的一段关于android应用程序进程的描述：

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By default, every application runs in its own Linux process. Android starts the process when any of the application's components need to be executed, then shuts down the process when it's no longer needed or when the system must recover memory for other applications.

每一个android应用默认都是在他自己的linux进程中运行。android操作系统会在这个android应用中的组件需要被执行的时候启动这个应用进程，并且会在这个应用进程没有任何组件执行或者是系统需要为其他应用申请更多内存的时候杀死这个应用进程。所以当我们需要启动这个应用的四大组件之一的时候如果这个应用的进程还没有启动，那么就会先启动这个应用程序进程。

本节主要是通过分析Activity的启动过程介绍应用程序进程的启动流程。

在上一篇文章中我们简要的介绍了Launcher的启动流程，在SystemServer进程执行完成，各种系统服务启动完成之后，会调用ActivityManagerService中的systemReady()方法，在systemReady（）方法中会执行Launcher启动的相关逻辑了，具体可以参考： android源码解析之（十）–>Launcher启动流程

Launcher应用程序在启动过程中会通过PackageManagerService服务请求查询系统所有的已安装应用的包名，图标和应用名称等信息，然后填充到Launcher中的Adapter中，这样点击某一项应用图标的时候就可以根据该图标的包名和启动Activity的类名初始化Intent对象，然后调用startActivity(Intent)启动相关的应用程序了。

其实android中应用进程可以通过许多方式启动，比如启动一个Activity，启动一个Service，启动一个ContentProvider或者是一个BroadcastReceiver，也就是说我们可以通过启动四大组件的方式启动应用进程，在应用进程没有启动的时候，如果我们通过启动这些组件，这时候系统会判断当前这些组件所需要的应用进程是否已经启动，若没有的话，则会启动应用进程。

这里我们通过Launcher简单分析一下应用进程的启动流程。通过上一篇Launcher启动流程，我们知道每一个launcher中的图标对应着一个应用报名和启动activity类名，查看LauncherActivity中的图标点击事件:

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protected void onListItemClick(ListView l, View v, int position, long id) {
Intent intent = intentForPosition(position);
startActivity(intent);
}

在通过应用包名和启动activity类名构造完成Intent之后，我们调用了startActivity方法来启动这个activity，很明显的，当前这个应用并没有启动，也就是说我们调用的startActivity方法不单单为我们启动了这个activity也同时在启动activity之前启动了这个应用进程，好了，那我们这里就以这个方法为入口分析一下应用进程的启动流程。

跟踪代码到Activity，发现其调用了startActivity的重载方法：

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@Override
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}

继续跟进：

Android基础

Android Zygote SystemServer gradle Launcher

阅读更多>>

2022-08-06

2022-08-06 32413714558925048e8725ce781fd94d 99+ 15 分钟 2.2 k

Launcher启动流程(转)

Launcher程序就是我们平时看到的桌面程序，它其实也是一个android应用程序，只不过这个应用程序是系统默认第一个启动的应用程序，这里我们就简单的分析一下Launcher应用的启动流程。

不同的手机厂商定制android操作系统的时候都会更改Launcher的源代码，我们这里以android23的源码为例大致的分析一下Launcher的启动流程。

通过上一篇文章，我们知道SystemServer进程主要用于启动系统的各种服务，二者其中就包含了负责启动Launcher的服务，LauncherAppService。具体关于SystenServer的启动流程可以参见： android源码解析之（九）–>SystemServer进程启动流程

在SystemServer进程的启动过程中会调用其main静态方法，开始执行整个SystemServer的启动流程，在其中通过调用三个内部方法分别启动boot service、core service和other service。在调用startOtherService方法中就会通过调用mActivityManagerService.systemReady()方法，那么我们看一下其具体实现：

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// We now tell the activity manager it is okay to run third party
// code. It will call back into us once it has gotten to the state
// where third party code can really run (but before it has actually
// started launching the initial applications), for us to complete our
// initialization.
mActivityManagerService.systemReady(new Runnable() {
@Override
public void run() {
Slog.i(TAG, "Making services ready");
mSystemServiceManager.startBootPhase(
SystemService.PHASE_ACTIVITY_MANAGER_READY);

try {
mActivityManagerService.startObservingNativeCrashes();
} catch (Throwable e) {
reportWtf("observing native crashes", e);
}

Slog.i(TAG, "WebViewFactory preparation");
WebViewFactory.prepareWebViewInSystemServer();

try {
startSystemUi(context);
} catch (Throwable e) {
reportWtf("starting System UI", e);
}
try {
if (networkScoreF != null) networkScoreF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Score Service ready", e);
}

try {
if (networkManagementF != null) networkManagementF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Managment Service ready", e);
}
try {
if (networkStatsF != null) networkStatsF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Stats Service ready", e);
}
try {
if (networkPolicyF != null) networkPolicyF.systemReady();
} catch (Throwable e) {
reportWtf("making Network Policy Service ready", e);
}
try {
if (connectivityF != null) connectivityF.systemReady();
} catch (Throwable e) {
reportWtf("making Connectivity Service ready", e);
}
try {
if (audioServiceF != null) audioServiceF.systemReady();
} catch (Throwable e) {
reportWtf("Notifying AudioService running", e);
}
Watchdog.getInstance().start();

// It is now okay to let the various system services start their
// third party code...
mSystemServiceManager.startBootPhase(
SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);

try {
if (wallpaperF != null) wallpaperF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying WallpaperService running", e);
}
try {
if (immF != null) immF.systemRunning(statusBarF);
} catch (Throwable e) {
reportWtf("Notifying InputMethodService running", e);
}
try {
if (locationF != null) locationF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying Location Service running", e);
}
try {
if (countryDetectorF != null) countryDetectorF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying CountryDetectorService running", e);
}
try {
if (networkTimeUpdaterF != null) networkTimeUpdaterF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying NetworkTimeService running", e);
}
try {
if (commonTimeMgmtServiceF != null) {
commonTimeMgmtServiceF.systemRunning();
}
} catch (Throwable e) {
reportWtf("Notifying CommonTimeManagementService running", e);
}
try {
if (textServiceManagerServiceF != null)
textServiceManagerServiceF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying TextServicesManagerService running", e);
}
try {
if (atlasF != null) atlasF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying AssetAtlasService running", e);
}
try {
// TODO(BT) Pass parameter to input manager
if (inputManagerF != null) inputManagerF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying InputManagerService running", e);
}
try {
if (telephonyRegistryF != null) telephonyRegistryF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying TelephonyRegistry running", e);
}
try {
if (mediaRouterF != null) mediaRouterF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying MediaRouterService running", e);
}

try {
if (mmsServiceF != null) mmsServiceF.systemRunning();
} catch (Throwable e) {
reportWtf("Notifying MmsService running", e);
}
}
});

可以发现这个方法传递了一个Runnable参数，里面执行了各种其他服务的systemReady方法，这里不是我们关注的重点，我们看一下在ActivityManagerService中systemReady方法的具体实现，方法体比较长，我就不在这里贴出代码了，主要的逻辑就是做一些ActivityManagerService的ready操作

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public void systemReady(final Runnable goingCallback) {
...
// Start up initial activity.
mBooting = true;
startHomeActivityLocked(mCurrentUserId, "systemReady");
...
}

重点是在这个方法体中调用了startHomeActivityLocked方法，看其名字就是说开始执行启动homeActivity的操作，好了，既然如此，我们再看一下startHomeActivityLocked的具体实现：

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boolean startHomeActivityLocked(int userId, String reason) {
if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL
&& mTopAction == null) {
// We are running in factory test mode, but unable to find
// the factory test app, so just sit around displaying the
// error message and don't try to start anything.
return false;
}
Intent intent = getHomeIntent();
ActivityInfo aInfo =
resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
if (aInfo != null) {
intent.setComponent(new ComponentName(
aInfo.applicationInfo.packageName, aInfo.name));
// Don't do this if the home app is currently being
// instrumented.
aInfo = new ActivityInfo(aInfo);
aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
ProcessRecord app = getProcessRecordLocked(aInfo.processName,
aInfo.applicationInfo.uid, true);
if (app == null || app.instrumentationClass == null) {
intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
mStackSupervisor.startHomeActivity(intent, aInfo, reason);
}
}

return true;
}

首先是调用getHomeIntent()方法，看一下getHomeIntent是如何实现构造Intent对象的：

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Intent getHomeIntent() {
Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
intent.setComponent(mTopComponent);
if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
intent.addCategory(Intent.CATEGORY_HOME);
}
return intent;
}

可以发现，启动Launcher的Intent对象中添加了Intent.CATEGORY_HOME常量，这个其实是一个launcher的标志，一般系统的启动页面Activity都会在androidmanifest.xml中配置这个标志。比如我们在github中的android launcher源码中查看其androidmanifest.xml文件：

可以发现其Activity的定义intentfilter中就是定义了这样的category。不同的手机厂商可能会修改Launcher的源码，但是这个category一般是不会更改的。

继续回到我们的startHomeActivityLocked方法，我们发现经过一系列的判断逻辑之后最后调用了mStackSupervisor.startHomeActivity方法，然后我们可以查看一下该方法的具体实现逻辑：

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void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason) {
moveHomeStackTaskToTop(HOME_ACTIVITY_TYPE, reason);
startActivityLocked(null /* caller */, intent, null /* resolvedType */, aInfo,
null /* voiceSession */, null /* voiceInteractor */, null /* resultTo */,
null /* resultWho */, 0 /* requestCode */, 0 /* callingPid */, 0 /* callingUid */,
null /* callingPackage */, 0 /* realCallingPid */, 0 /* realCallingUid */,
0 /* startFlags */, null /* options */, false /* ignoreTargetSecurity */,
false /* componentSpecified */,
null /* outActivity */, null /* container */, null /* inTask */);
if (inResumeTopActivity) {
// If we are in resume section already, home activity will be initialized, but not
// resumed (to avoid recursive resume) and will stay that way until something pokes it
// again. We need to schedule another resume.
scheduleResumeTopActivities();
}
}

发现其调用的是scheduleResumeTopActivities()方法，这个方法其实是关于Activity的启动流程的逻辑了，这里我们不在详细的说明，关于Activity的启动流程我们在下面的文章中会介绍。

因为我们的Launcher启动的Intent是一个隐士的Intent，所以我们会启动在androidmanifest.xml中配置了相同catogory的activity，android M中配置的这个catogory就是LauncherActivity。

LauncherActivity继承与ListActivity，我们看一下其Layout布局文件：

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<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
>

<ListView
android:id="@android:id/list"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>

<TextView
android:id="@android:id/empty"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:text="@string/activity_list_empty"
android:visibility="gone"
android:textAppearance="?android:attr/textAppearanceMedium"
/>

</FrameLayout>

可以看到我们现实的桌面其实就是一个ListView控件，然后看一下其onCreate方法：

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@Override
protected void onCreate(Bundle icicle) {
super.onCreate(icicle);

mPackageManager = getPackageManager();

if (!mPackageManager.hasSystemFeature(PackageManager.FEATURE_WATCH)) {
requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
setProgressBarIndeterminateVisibility(true);
}
onSetContentView();

mIconResizer = new IconResizer();

mIntent = new Intent(getTargetIntent());
mIntent.setComponent(null);
mAdapter = new ActivityAdapter(mIconResizer);

setListAdapter(mAdapter);
getListView().setTextFilterEnabled(true);

updateAlertTitle();
updateButtonText();

if (!mPackageManager.hasSystemFeature(PackageManager.FEATURE_WATCH)) {
setProgressBarIndeterminateVisibility(false);
}
}

可以看到在LauncherActivity的onCreate方法中初始化了一个PackageManager，其主要作用就是从中查询出系统所有已经安装的应用列表，应用包名，应用图标等信息。然后将这些信息注入到Adapter中，这样就可以将系统应用图标和名称显示出来了。
在系统的回调方法onListItemClick中

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@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
Intent intent = intentForPosition(position);
startActivity(intent);
}

这也就是为什么我们点击了某一个应用图标之后可以启动某一项应用的原因了，我们看一下这里的intentForPosition是如何实现的。

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protected Intent intentForPosition(int position) {
ActivityAdapter adapter = (ActivityAdapter) mAdapter;
return adapter.intentForPosition(position);
}

这里又调用了adapter的intentForPosition方法：

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public Intent intentForPosition(int position) {
if (mActivitiesList == null) {
return null;
}

Intent intent = new Intent(mIntent);
ListItem item = mActivitiesList.get(position);
intent.setClassName(item.packageName, item.className);
if (item.extras != null) {
intent.putExtras(item.extras);
}
return intent;
}

可以看到由于adapter的每一项中都保存了应用的包名可启动Activity名称，所以这里在初始化Intent的时候，直接将这些信息注入到Intent中，然后调用startActivity，就将这些应用启动了（关于startActivity是如何启动的下面的文章中我将介绍）。

总结：

Launcher的启动流程

Zygote进程 –> SystemServer进程 –> startOtherService方法 –> ActivityManagerService的systemReady方法 –> startHomeActivityLocked方法 –> ActivityStackSupervisor的startHomeActivity方法 –> 执行Activity的启动逻辑，执行scheduleResumeTopActivities()方法。。。。

因为是隐士的启动Activity，所以启动的Activity就是在AndroidManifest.xml中配置catogery的值为：

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public static final String CATEGORY_HOME = "android.intent.category.HOME";

可以发现android M中在androidManifest.xml中配置了这个catogory的activity是LauncherActivity，所以我们就可以将这个Launcher启动起来了

LauncherActivity中是以ListView来显示我们的应用图标列表的，并且为每个Item保存了应用的包名和启动Activity类名，这样点击某一项应用图标的时候就可以根据应用包名和启动Activity名称启动我们的App了。

另外对android源码解析方法感兴趣的可参考我的：

android源码解析之（一）–>android项目构建过程

 android源码解析之（二）–>异步消息机制

 android源码解析之（三）–>异步任务AsyncTask

android源码解析之（四）–>HandlerThread

android源码解析之（五）–>IntentService

android源码解析之（六）–>Log

android源码解析之（七）–>LruCache

android源码解析之（八）–>Zygote进程启动流程

 android源码解析之（九）–>SystemServer进程启动流程

Android基础

Android Zygote SystemServer gradle Launcher

2022-08-06 a0df956d4093c3a212ac41673146cba8 99+ 24 分钟 3.6 k

SystemServer进程启动流程(转)

转载请标明出处：一片枫叶的专栏

上面一文中我们讲过android系统中比较重要的几个进程：init进程，Zygote进程，SystemServer进程已经各种应用进程，其中Zygote进程是整个android系统的根进程，包含SystemServer进程已经各种应用进程在内的进程都是通过Zygote进程fork出来的，具体可参见： android源码解析之（八）–>Zygote进程启动流程
那么SystemServer进程是做什么用的呢？

其实SystemServer进程主要的作用是在这个进程中启动各种系统服务，比如ActivityManagerService，PackageManagerService，WindowManagerService服务，以及各种系统性的服务其实都是在SystemServer进程中启动的，而当我们的应用需要使用各种系统服务的时候其实也是通过与SystemServer进程通讯获取各种服务对象的句柄的。

由上一篇文章我们知道SystemServer进程其实也是有Zygote进程fork出来的，并且执行其main方法，那么这里我们以android23的源码为例，看一下SystemServer的main方法的执行逻辑：

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/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}

这里比较简单，只是new出一个SystemServer对象并执行其run方法，查看SystemServer类的定义我们知道其实final类型的，所以我们一般不能重写或者继承。

然后我们查看run方法：

Android基础

Android Zygote SystemServer gradle init进程

阅读更多>>

2022-08-06

2022-08-06 6ede63bc39329533a3d6db9f65785eea 99+ 9 分钟 1.3 k

Zygote进程启动流程(转)

大家都知道android系统的Zygote进程是所有的android进程的父进程，包括SystemServer和各种应用进程都是通过Zygote进程fork出来的。Zygote（孵化）进程相当于是android系统的根进程，后面所有的进程都是通过这个进程fork出来的，而Zygote进程则是通过linux系统的init进程启动的，也就是说，android系统中各种进程的启动方式

init进程 –> Zygote进程 –> SystemServer进程 –>各种应用进程

init进程：linux的根进程，android系统是基于linux系统的，因此可以算作是整个android操作系统的第一个进程；

Zygote进程：android系统的根进程，主要作用：可以作用Zygote进程fork出SystemServer进程和各种应用进程；

SystemService进程：主要是在这个进程中启动系统的各项服务，比如ActivityManagerService，PackageManagerService，WindowManagerService服务等等；

各种应用进程：启动自己编写的客户端应用时，一般都是重新启动一个应用进程，有自己的虚拟机与运行环境；

本文主要介绍一下Zygote进程的启动流程，关于SystenServer进程和各种应用进程的启动方式会在以后的文章中介绍。

init进程在启动Zygote进程时一般都会调用ZygoteInit类的main方法，因此我们这里看一下该方法的具体实现(基于android23源码)；

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public static void main(String argv[]) {
try {
RuntimeInit.enableDdms();
// Start profiling the zygote initialization.
SamplingProfilerIntegration.start();

boolean startSystemServer = false;
String socketName = "zygote";
String abiList = null;
for (int i = 1; i < argv.length; i++) {
if ("start-system-server".equals(argv[i])) {
startSystemServer = true;
} else if (argv[i].startsWith(ABI_LIST_ARG)) {
abiList = argv[i].substring(ABI_LIST_ARG.length());
} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
socketName = argv[i].substring(SOCKET_NAME_ARG.length());
} else {
throw new RuntimeException("Unknown command line argument: " + argv[i]);
}
}

if (abiList == null) {
throw new RuntimeException("No ABI list supplied.");
}

registerZygoteSocket(socketName);
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
preload();
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
SystemClock.uptimeMillis());

// Finish profiling the zygote initialization.
SamplingProfilerIntegration.writeZygoteSnapshot();

// Do an initial gc to clean up after startup
gcAndFinalize();

// Disable tracing so that forked processes do not inherit stale tracing tags from
// Zygote.
Trace.setTracingEnabled(false);

if (startSystemServer) {
startSystemServer(abiList, socketName);
}

Log.i(TAG, "Accepting command socket connections");
runSelectLoop(abiList);

closeServerSocket();
} catch (MethodAndArgsCaller caller) {
caller.run();
} catch (RuntimeException ex) {
Log.e(TAG, "Zygote died with exception", ex);
closeServerSocket();
throw ex;
}
}

Android基础

Android Zygote SystemServer gradle init进程

阅读更多>>

2022-08-06

2022-08-06 5443f92724bad1557763838747dd903b 99+ 19 分钟 2.8 k

android之LruCache(转)

android开发过程中经常会用到缓存，现在主流的app中图片等资源的缓存策略一般是分两级，一个是内存级别的缓存，一个是磁盘级别的缓存。

作为android系统的维护者google也开源了其缓存方案，LruCache和DiskLruCache。从android3.1开始LruCache已经作为android源码的一部分维护在android系统中，为了兼容以前的版本android的support-v4包也提供了LruCache的维护，如果App需要兼容到android3.1之前的版本就需要使用support-v4包中的LruCache，如果不需要兼容到android3.1则直接使用android源码中的LruCache即可，这里需要注意的是DiskLruCache并不是android源码的一部分。

在LruCache的源码中，关于LruCache有这样的一段介绍：

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A cache that holds strong references to a limited number of values. Each time a value is accessed, it is moved to the head of a queue. When a value is added to a full cache, the value at the end of that queue is evicted and may become eligible for garbage collection.

cache对象通过一个强引用来访问内容。每次当一个item被访问到的时候，这个item就会被移动到一个队列的队首。当一个item被添加到已经满了的队列时，这个队列的队尾的item就会被移除。

其实这个实现的过程就是LruCache的缓存策略，即Lru–>(Least recent used)最少最近使用算法。

下面我们具体看一下LruCache的实现：

Android基础

Android gradle LruCache

阅读更多>>

2022-08-06

应用进程Context创建流程(转)

activity销毁流程(转)

activity启动流程(转)

apk安装流程(转)

系统启动并解析Manifest的流程(转)

应用进程启动流程(转)

Launcher启动流程(转)

SystemServer进程启动流程(转)

Zygote进程启动流程(转)

android之LruCache(转)

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