简单跟一下MediaSession源码4

frameworks\base\core\java\com\android\internal\policy\PhoneFallbackEventHandler.java

public void setView(View v);
public void preDispatchKeyEvent(KeyEvent event);
public boolean dispatchKeyEvent(KeyEvent event);

public boolean dispatchKeyEvent(KeyEvent event) {
    final int action = event.getAction();
    final int keyCode = event.getKeyCode();
    if (action == KeyEvent.ACTION_DOWN) {
        return onKeyDown(keyCode, event);
    } else {
        return onKeyUp(keyCode, event);
    }
}

private int processKeyEvent(QueuedInputEvent q) {
    //下面都是看是否需要消费
    final KeyEvent event = (KeyEvent)q.mEvent;
    if (mUnhandledKeyManager.preViewDispatch(event)) {
        return FINISH_HANDLED;
    }
    if (mView.dispatchKeyEvent(event)) {
        return FINISH_HANDLED;
    }
    if (shouldDropInputEvent(q)) {
        return FINISH_NOT_HANDLED;
    }
    if (mUnhandledKeyManager.dispatch(mView, event)) {
        return FINISH_HANDLED;
    }
    //略
    //调用mFallbackEventHandler查看是否需要消费
    //这里消费了，因为符合条件。
    if (mFallbackEventHandler.dispatchKeyEvent(event)) {
        return FINISH_HANDLED;
    }
    //略，后续的后续有机会分析，暂时不走下面
    return FORWARD;
}

@Override
protected int onProcess(QueuedInputEvent q) {
    //当前发送的event是KeyEvent的实例
    if (q.mEvent instanceof KeyEvent) {
        //走这里
        return processKeyEvent(q);
    } else {
        final int source = q.mEvent.getSource();
        if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {
            return processPointerEvent(q);
        } else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
            return processTrackballEvent(q);
        } else {
            return processGenericMotionEvent(q);
        }
    }
}

public final void deliver(QueuedInputEvent q) {
    ViewDebugConfig.getInstance().debugInputStageDeliverd(this,
            System.currentTimeMillis());
    //看一下消费
    if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {
        forward(q);
    } else if (shouldDropInputEvent(q)) {
        finish(q, false);
    } else {
        //走这里，我们这是88键值且为down事件
        traceEvent(q, Trace.TRACE_TAG_VIEW);
        final int result;
        try {
            //进入onProcess()处理流程，这里result返回值为0
            result = onProcess(q);
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
        // 接着进入
        apply(q, result);
    }
}

protected void apply(QueuedInputEvent q, int result) {
    if (result == FORWARD) {
        forward(q);
    } else if (result == FINISH_HANDLED) {
        finish(q, true);
    } else if (result == FINISH_NOT_HANDLED) {
        finish(q, false);
    } else {
        throw new IllegalArgumentException("Invalid result: " + result);
    }
}

protected void forward(QueuedInputEvent q) {
    onDeliverToNext(q);
}

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
        int userId) {
    synchronized (this) {
        if (mView == null) {
            mView = view;
            //略
            //初始化InputStage子类
            InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);
            InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,
                    "aq:native-post-ime:" + counterSuffix);
            InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);
            InputStage imeStage = new ImeInputStage(earlyPostImeStage,
                    "aq:ime:" + counterSuffix);
            InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);
            InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,
                    "aq:native-pre-ime:" + counterSuffix);
​
            mFirstInputStage = nativePreImeStage;
            mFirstPostImeInputStage = earlyPostImeStage;
            
            //略
        }
    }
}

protected void onDeliverToNext(QueuedInputEvent q) {
    //如果mNext不为null，走这里
    if (mNext != null) {
        mNext.deliver(q);
    } else {
        finishInputEvent(q);
    }
}

private void deliverInputEvent(QueuedInputEvent q) {
    //略
    try {
        //略
        InputStage stage;
        if (q.shouldSendToSynthesizer()) {
            stage = mSyntheticInputStage;
        } else {
            stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
        }
        //这里的mEvent是KeyEvent对象，我们这里只看发送的上一曲88事件
        if (q.mEvent instanceof KeyEvent) {
            try {
                mUnhandledKeyManager.preDispatch((KeyEvent) q.mEvent);
            } finally {
                Trace.traceEnd(Trace.TRACE_TAG_VIEW);
            }
        }
        //不为null
        if (stage != null) {
            //处理窗口焦点变化
            handleWindowFocusChanged();
            //调用了deliver()
            stage.deliver(q);
        } else {
            finishInputEvent(q);
        }
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_VIEW);
    }
}

void doProcessInputEvents() {
    while (mPendingInputEventHead != null) {
        //队列，所有先赋值，然后取下一个
        QueuedInputEvent q = mPendingInputEventHead;
        //取下一个
        mPendingInputEventHead = q.mNext;
        //如果为null，把尾置为null
        if (mPendingInputEventHead == null) {
            mPendingInputEventTail = null;
        }
        q.mNext = null;
        //计数器减去一
        mPendingInputEventCount -= 1;
        mViewFrameInfo.setInputEvent(mInputEventAssigner.processEvent(q.mEvent));
        //调用deliverInputEvent处理队列中的QueuedInputEvent
        deliverInputEvent(q);
    }
    if (mProcessInputEventsScheduled) {
        mProcessInputEventsScheduled = false;
        mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);
    }
}

@UnsupportedAppUsage
void enqueueInputEvent(InputEvent event,
        InputEventReceiver receiver, int flags, boolean processImmediately) {
    //把事件添加到QueuedInputEvent
    QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
    //看是否MotionEvent类型事件
    if (event instanceof MotionEvent) {
        MotionEvent me = (MotionEvent) event;
        if (me.getAction() == MotionEvent.ACTION_CANCEL) {
            EventLog.writeEvent(EventLogTags.VIEW_ENQUEUE_INPUT_EVENT, "Motion - Cancel",
                    getTitle().toString());
        }
    } else if (event instanceof KeyEvent) {
        //KeyEvent事件
        KeyEvent ke = (KeyEvent) event;
    }
    QueuedInputEvent last = mPendingInputEventTail;
    //如果队列尾为null，也就是里面没有数据，赋值
    if (last == null) {
        //这里赋值mPendingInputEventHead和mPendingInputEventTail
        mPendingInputEventHead = q;
        mPendingInputEventTail = q;
    } else {
        last.mNext = q;
        mPendingInputEventTail = q;
    }
    //事件计数器+1
    mPendingInputEventCount += 1;
    //传入的是true，立即处理
    if (processImmediately) {
        doProcessInputEvents();
    } else {
        scheduleProcessInputEvents();
    }
}

@Override
public void onInputEvent(InputEvent event) {
    ViewDebugConfig.getInstance().debugInputEventStart(event);
    List<InputEvent> processedEvents;
    try {
        //方法中有对事件类型判断，如果不是MotionEvent，一定返回null
        //我们这里是Keyevent事件
        processedEvents =
            mInputCompatProcessor.processInputEventForCompatibility(event);
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_VIEW);
    }
    //processedEvents为null
    if (processedEvents != null) {
        //略
    } else {
        //dropIfNeeded()返回的是false，反一下就为true，调用enqueueInputEvent
        if (!dropIfNeeded(event)) {
            enqueueInputEvent(event, this, 0, true);
        } else {
            finishInputEvent(event, true);
        }
    }
}