Android事件分发流程（API-27）（一）

一个点击引起的世界大战

有一个WMS（WindowManagerService）的大管家掌管着Android系统的键盘消息，他有个属性叫mInputManager（IMS，InputManagerService），是Android的输入管理器，属于Java层输入管理器，同时他指向着C++层中的输入管理器InputManager来监控系统的键盘消息（来自《Android系统源代码情景分析 第三版》）

当我们在屏幕上的点击，经过WMS，IMS，到native层，最后会回调到Java层的InputEventReceiver.dispatchInputEvent(int seq, InputEvent event, int displayId)，一步步调用到Activity.dispatchTouchEvent()

• 序列图
• 

  Android触摸流程.jpg

• InputEventReceiver.dispatchInputEvent(int seq, InputEvent event, int displayId)

  // Called from native code.
  @SuppressWarnings("unused")
  private void dispatchInputEvent(int seq, InputEvent event, int displayId) {
      mSeqMap.put(event.getSequenceNumber(), seq);
      onInputEvent(event, displayId);
  }
  

• InputEventReceiver是abstract class，在ViewRootImpl中有个内部类叫WindowInputEventReceiver继承InputEventReceiver

  final class WindowInputEventReceiver extends InputEventReceiver {
      public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
          super(inputChannel, looper);
      }
  
      @Override
      public void onInputEvent(InputEvent event, int displayId) {
          // native 回调在这里
          enqueueInputEvent(event, this, 0, true);
      }
      ...
  }
  

• onInputEvent()方法中调用enqueueInputEvent()

  void enqueueInputEvent(InputEvent event,
                         InputEventReceiver receiver, int flags, boolean processImmediately) {
      adjustInputEventForCompatibility(event);
      QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
  
      // Always enqueue the input event in order, regardless of its time stamp.
      // We do this because the application or the IME may inject key events
      // in response to touch events and we want to ensure that the injected keys
      // are processed in the order they were received and we cannot trust that
      // the time stamp of injected events are monotonic.
      QueuedInputEvent last = mPendingInputEventTail;
      if (last == null) {
          mPendingInputEventHead = q;
          mPendingInputEventTail = q;
      } else {
          last.mNext = q;
          mPendingInputEventTail = q;
      }
      mPendingInputEventCount += 1;
      Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
                         mPendingInputEventCount);
      // 上面的传参是true，调用doProcessInputEvents()
      if (processImmediately) {
          doProcessInputEvents();
      } else {
          scheduleProcessInputEvents();
      }
  }
  

• 进入doProcessInputEvents

  void doProcessInputEvents() {
      // Deliver all pending input events in the queue.
      while (mPendingInputEventHead != null) {
          QueuedInputEvent q = mPendingInputEventHead;
          mPendingInputEventHead = q.mNext;
          if (mPendingInputEventHead == null) {
              mPendingInputEventTail = null;
          }
          q.mNext = null;
  
          mPendingInputEventCount -= 1;
          Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
                             mPendingInputEventCount);
  
          long eventTime = q.mEvent.getEventTimeNano();
          long oldestEventTime = eventTime;
          if (q.mEvent instanceof MotionEvent) {
              MotionEvent me = (MotionEvent)q.mEvent;
              if (me.getHistorySize() > 0) {
                  oldestEventTime = me.getHistoricalEventTimeNano(0);
              }
          }
          mChoreographer.mFrameInfo.updateInputEventTime(eventTime, oldestEventTime);
          
          // 到这
          deliverInputEvent(q);
      }
  
      // We are done processing all input events that we can process right now
      // so we can clear the pending flag immediately.
      if (mProcessInputEventsScheduled) {
          mProcessInputEventsScheduled = false;
          mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);
      }
  }
  
  
  

• 进入deliverInputEvent()

  private void deliverInputEvent(QueuedInputEvent q) {
      Trace.asyncTraceBegin(Trace.TRACE_TAG_VIEW, "deliverInputEvent",
                            q.mEvent.getSequenceNumber());
      if (mInputEventConsistencyVerifier != null) {
          mInputEventConsistencyVerifier.onInputEvent(q.mEvent, 0);
      }
  
      InputStage stage;
      if (q.shouldSendToSynthesizer()) {
          stage = mSyntheticInputStage;
      } else {
          stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
      }
  
      if (stage != null) {
          // 到这
          stage.deliver(q);
      } else {
          finishInputEvent(q);
      }
  }
  

• 这里的stage是ViewPostImeInputStage继承InputStage

  /**
       * Delivers post-ime input events to the view hierarchy.
       */
  final class ViewPostImeInputStage extends InputStage {
      public ViewPostImeInputStage(InputStage next) {
          super(next);
      }
  
      @Override
      protected int onProcess(QueuedInputEvent q) {
          if (q.mEvent instanceof KeyEvent) {
              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);
              }
          }
      }
  
      ...
          
      private int processPointerEvent(QueuedInputEvent q) {
          final MotionEvent event = (MotionEvent)q.mEvent;
  
          mAttachInfo.mUnbufferedDispatchRequested = false;
          mAttachInfo.mHandlingPointerEvent = true;
          // 这里的mView是DecorView
          boolean handled = mView.dispatchPointerEvent(event);
          maybeUpdatePointerIcon(event);
          maybeUpdateTooltip(event);
          mAttachInfo.mHandlingPointerEvent = false;
          if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {
              mUnbufferedInputDispatch = true;
              if (mConsumeBatchedInputScheduled) {
                  scheduleConsumeBatchedInputImmediately();
              }
          }
          return handled ? FINISH_HANDLED : FORWARD;
      }
  
      ...
  }
  

• dispatchPointerEvent在view中实现

  /**
   * Dispatch a pointer event.
   * <p>
   * Dispatches touch related pointer events to {@link #onTouchEvent(MotionEvent)} and all
   * other events to {@link #onGenericMotionEvent(MotionEvent)}.  This separation of concerns
   * reinforces the invariant that {@link #onTouchEvent(MotionEvent)} is really about touches
   * and should not be expected to handle other pointing device features.
   * </p>
   *
   * @param event The motion event to be dispatched.
   * @return True if the event was handled by the view, false otherwise.
   * @hide
   */
  public final boolean dispatchPointerEvent(MotionEvent event) {
      if (event.isTouchEvent()) {
          // 调用dispatchTouchEvent
          return dispatchTouchEvent(event);
      } else {
          return dispatchGenericMotionEvent(event);
      }
  }
  

• dispatchTouchEvent，注意这里的Window.Callback就是Activity，

  @Override
  public boolean dispatchTouchEvent(MotionEvent ev) {
      final Window.Callback cb = mWindow.getCallback();
      return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
          ? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
  }
  

• 到Activity.dispatchTouchEvent

Activity.dispatchTouchEvent()之后就是我们熟悉的事件分发了

详情见Android事件分发流程（API-27）（二）

• 参考资料
  • 《Android系统源代码情景分析 第三版》
  • 从你触摸屏幕开始分析android触摸事件分发