@Override
    public KeyEvent dispatchUnhandledKey(WindowState win, KeyEvent event, int policyFlags) {
        ...
        KeyEvent fallbackEvent = null;
        if ((event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
            final KeyCharacterMap kcm = event.getKeyCharacterMap();
            final int keyCode = event.getKeyCode();
            final int metaState = event.getMetaState();
            final boolean initialDown = event.getAction() == KeyEvent.ACTION_DOWN
                    && event.getRepeatCount() == 0;

            // Check for fallback actions specified by the key character map.
            final FallbackAction fallbackAction;
            if (initialDown) {
                fallbackAction = kcm.getFallbackAction(keyCode, metaState);
            } else {
                fallbackAction = mFallbackActions.get(keyCode);
            }

            if (fallbackAction != null) {
                if (DEBUG_INPUT) {
                    Slog.d(TAG, "Fallback: keyCode=" + fallbackAction.keyCode
                            + " metaState=" + Integer.toHexString(fallbackAction.metaState));
                }

                final int flags = event.getFlags() | KeyEvent.FLAG_FALLBACK;
                fallbackEvent = KeyEvent.obtain(
                        event.getDownTime(), event.getEventTime(),
                        event.getAction(), fallbackAction.keyCode,
                        event.getRepeatCount(), fallbackAction.metaState,
                        event.getDeviceId(), event.getScanCode(),
                        flags, event.getSource(), null);

                if (!interceptFallback(win, fallbackEvent, policyFlags)) {
                    fallbackEvent.recycle();
                    fallbackEvent = null;
                }

                if (initialDown) {
                    mFallbackActions.put(keyCode, fallbackAction);
                } else if (event.getAction() == KeyEvent.ACTION_UP) {
                    mFallbackActions.remove(keyCode);
                    fallbackAction.recycle();
                }
            }
        }

        if (DEBUG_INPUT) {
            if (fallbackEvent == null) {
                Slog.d(TAG, "No fallback.");
            } else {
                Slog.d(TAG, "Performing fallback: " + fallbackEvent);
            }
        }
        return fallbackEvent;
    }

Handy class for starting a new thread that has a looper. The looper can then be used to create handler classes. Note that start() must still be called.

HandlerThread mHandlerThread = new HandlerThread("myHandlerThreand");
        mHandlerThread.start();

        // 创建的Handler将会在mHandlerThread线程中执行
        final Handler mHandler = new Handler(mHandlerThread.getLooper()) {
            @Override
            public void handleMessage(Message msg) {
                Log.i("tag", "接收到消息：" + msg.obj.toString());
            }
        };

        title = (TextView) findViewById(R.id.title);
        title.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Message msg = new Message();
                msg.obj = "11111";
                mHandler.sendMessage(msg);

                msg = new Message();
                msg.obj = "2222";
                mHandler.sendMessage(msg);
            }
        });