Android中onInterceptTouchEvent、dispatchTouchEvent及onTouchEvent的调用顺序及内部原理

在Android中需要经常对用户手势进行判断，在判断手势时需要精细的分清楚每个触摸事件以及每个View对事件的接收情况，在View，ViewGroup，Activity中都可以接收事件，在对事件进行处理时onInterceptTouchEvent、dispatchTouchEvent及onTouchEvent这三个函数的调用顺序及关系需要好好理清楚。原理代码有点多，如果不对着具体事例，理解起来很难。下面对着代码进行分析。代码地址为：https://github.com/huangtianyu/DispatchTouchEvent，记得帮忙点Star

MainActivity.java

package com.zqc.dispatchtouchevent;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

import static com.zqc.dispatchtouchevent.Constants.TAG;

public class MainActivity extends Activity implements View.OnTouchListener {
    private MyView myView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.e(TAG, "MainActivity onCreate");
        setContentView(R.layout.activity_main);
        myView = (MyView) findViewById(R.id.myview);
        myView.setOnTouchListener(MainActivity.this);
    }
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.e(TAG, "MainActivity dispatchTouchEvent");
        return super.dispatchTouchEvent(ev);
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e(TAG, "MainActivity onTouchEvent");
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.e(TAG, "MainActivity onTouchEvent ACTION_DOWN");
                break;
            case MotionEvent.ACTION_MOVE:
                Log.e(TAG, "MainActivity onTouchEvent ACTION_MOVE");
                break;
            case MotionEvent.ACTION_CANCEL:
                Log.e(TAG, "MainActivity onTouchEvent ACTION_CANCEL");
                break;
            case MotionEvent.ACTION_UP:
                Log.e(TAG, "MainActivity onTouchEvent ACTION_UP");
                break;
            default:
                Log.e(TAG, "MainActivity onTouchEvent " + event.getAction());
                break;
        }
        return super.onTouchEvent(event);
    }
    @Override
    protected void onResume() {
        Log.e(TAG, "MainActivity onResume");
        super.onResume();
    }
    @Override
    protected void onPause() {
        Log.e(TAG, "MainActivity onPause");
        super.onPause();
    }
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        Log.e(TAG, "MainActivity onTouch");
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                Log.e(TAG, "MainActivity onTouch ACTION_DOWN");
                break;
            case MotionEvent.ACTION_MOVE:
                Log.e(TAG, "MainActivity onTouch ACTION_MOVE");
                break;
            case MotionEvent.ACTION_CANCEL:
                Log.e(TAG, "MainActivity onTouch ACTION_CANCEL");
                break;
            case MotionEvent.ACTION_UP:
                Log.e(TAG, "MainActivity onTouch ACTION_UP");
                break;
            default:
                Log.e(TAG, "MainActivity onTouchEvent " + event.getAction());
                break;
        }
        return false;
    }
}

MyView.java

package com.zqc.dispatchtouchevent;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.widget.TextView;

import static com.zqc.dispatchtouchevent.Constants.MY_GESTURE_TAG;
import static com.zqc.dispatchtouchevent.Constants.TAG;


public class MyView extends TextView {
    private Context mContext;
    //private GestureDetector mGesture;

    public MyView(Context context) {
        this(context, null);
    }

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        Log.e(TAG, "MyView");
        mContext = context;
        //手势初始化
       // mGesture = new GestureDetector(mContext, mGestureListener);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e(TAG, "MyView onTouchEvent");
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.e(TAG, "MyView onTouchEvent ACTION_DOWN");
                break;
            case MotionEvent.ACTION_MOVE:
                Log.e(TAG, "MyView onTouchEvent ACTION_MOVE");
                break;
            case MotionEvent.ACTION_CANCEL:
                Log.e(TAG, "MyView onTouchEvent ACTION_CANCEL");
                break;
            case MotionEvent.ACTION_UP:
                Log.e(TAG, "MyView onTouchEvent ACTION_UP");
                break;
            default:
                Log.e(TAG, "MyView onTouchEvent " + event.getAction());
                break;
        }
//        设置手势监听
       // mGesture.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        Log.e(TAG, "MyView dispatchTouchEvent");
        return super.dispatchTouchEvent(event);
    }
}

MyViewGroup.java

package com.zqc.dispatchtouchevent;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.RelativeLayout;

import static com.zqc.dispatchtouchevent.Constants.TAG;

public class MyViewGroup extends RelativeLayout {
    public MyViewGroup(Context context) {
        this(context, null);
    }

    public MyViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
        Log.e(TAG, "MyViewGroup");
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        Log.e(TAG, "MyViewGroup onInterceptTouchEvent");
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.e(TAG, "MyViewGroup dispatchTouchEvent");
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e(TAG, "MyViewGroup onTouchEvent");
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.e(TAG, "MyViewGroup onTouchEvent ACTION_DOWN");
                break;
            case MotionEvent.ACTION_MOVE:
                Log.e(TAG, "MyViewGroup onTouchEvent ACTION_MOVE");
                break;
            case MotionEvent.ACTION_CANCEL:
                Log.e(TAG, "MyViewGroup onTouchEvent ACTION_CANCEL");
                break;
            case MotionEvent.ACTION_UP:
                Log.e(TAG, "MyViewGroup onTouchEvent ACTION_UP");
                break;
            default:
                Log.e(TAG, "MyViewGroup onTouchEvent " + event.getAction());
                break;
        }
        return super.onTouchEvent(event);
    }
}

Contants.java

package com.zqc.dispatchtouchevent;

public class Constants {

    public final static String TAG = "MY_LOG";
    public final static String MY_GESTURE_TAG = "GESTURE_TAG";
}

在代码中将每个函数分别列出并加上Log输出，这样对着Log日志进行分析，则一目了然。

1.让所有的onInterceptTouchEvent、dispatchTouchEvent及onTouchEvent均返回super.onTouchEvent即均返回false时，轻轻点击MyView然后快速抬起，查看相应的Log：

 

通过Log能清楚的查看代码执行的流程，具体流程如下：

DOWN事件：MainActivity.dispatchTouchEvent->MyViewGroup.dispatchTouchEvet->MyViewGroup.onInterceptTouchEvent->MyView.dispatchTouchEvent->setOnTouchListener.onTouch->MyView.onTouchEvent->MyViewGroup.onTouchEvent->MainActivity.onTouchEvent

UP事件：MainActivity.dispatchTouchEvent->MainActivity.onTouchEvent

从上面流程可以看出，点击事件最先传给窗口Activity的dispatchTouchEvent函数进行事件分发，然后对于View类，是先传给对应的父View的dispatchTouchEvent进行事件分发，然后在传给里面点击的View。当down事件没有被各个view消费时，最终会调用Acitivity的onTouchEvent，并在在Down后续的UP事件不在传给MyViewGroup和MyView，直接传给MainAcitivity。所以当事件没有被窗口中的View消费时，最终都是给了该窗口Activity类中的onTouchEvent事件处理。从Log中也可以看出setOnTouchListener中的onTouch事件是在对应View的onTouchEvent事件之前被执行。

2.当MainAcivity中dispathTouchEvent返回true时，轻轻点击MyView，查看对应Log：

通过Log可以看到当窗口Activity的dispatchTouchEvent返回true时，DOWN事件没有往View中传，也就没有调用任何的onTouchEvent事件，UP事件也是走到Activity的dispatchTouchEvent时也就结束了。

3.重新置Activity中dispatchTouchEvent返回false，然后置ViewGroup中onInterceptTouchEvent返回true时，轻轻点击MyView查看对应Log：

这时DOWN事件和UP事件的执行流程如下：

DOWN事件：MainActivity.dipatchTouchEvent->MyViewGroup.dispatchTouchEvent->MyViewGroup.onInterceptTouchEvent->MyViewGroup.onTouchEvent->MainActivity.onTouchEvent.

UP事件:MainActiviy.dispatchTouchEvent->MainActivity.onTouchEvent.

从Log中可以看出，当onInterceptTouchEvent返回true时，事件即被MyViewGroup拦截了，这时事件就直接传给MyViewGroup.onTouchEvent，不在往子View传，由于MyViewGroup.onTouchEvent返回的是false，即MyViewGroup并没有消费事件，这时事件会传给窗口Activity，UP事件会传给最后一个接受Down事件的窗口或View。

4.当MyView中onTouchEvent返回true时，即MyView会消费传给他的事件。轻点MyView查看对应的Log：

继续分析DOWN事件的流程：

DOWN事件：MainActivity.dispatchTouchEvent->MyViewGroup.dispatchTouchEvet->MyViewGroup.onInterceptTouchEvent->MyView.dispatchTouchEvent->setOnTouchListener.onTouch->MyView.onTouchEvent

UP事件：MainActivity.dispatchTouchEvent->MyViewGroup.dispatchTouchEvet->MyViewGroup.onInterceptTouchEvent->MyView.dispatchTouchEvent->setOnTouchListener.onTouch->MyView.onTouchEvent

从上面的执行流程可以看出当事件被MyView消费后，事件不会在往上传，后续的UP事件也直接通过dispatchTouchEvent分发给对应的View，这里还是提一下，在MainAcitivy中设置的setOnTouchListener中的onTouch事件是在MyView自身的onTouchEvent事件之前被执行，因而设置的setOnTouchEvent的onTouch函数还是会被执行。

先只分析这几种场景，MOVE事件和UP事件一样只要DOWN事件被某个View消耗了，那么MOVE事件也就直接传到这个View。可以下载代码运行后，在MyView上面滑动下看下Log，具体Log我也贴一份。

情况1：

情况2：

下面对着Android源码来具体分析View的触摸事件到底是怎么执行的。首先根据Log可以最先接收到消息的是Activity的dispatchTouchEvent，在该处设置断点，然后查看对应的调用方法栈（你会发现在调到MainActivity的dispatchTouchEvent时，前面已经调用了很多方法），如下：

由于Android系统启动后会先启动Zygote进程，该进程会在手机开机后一直运行，Android中的几个系统服务都是由Zygote进程fork出来的，一个应用在启动时所分配到的进程也是由Zygote进程fork出来的，通常说一个应用的起点是Application里面的onCreate函数，其实真正的起点是ActivityThread里面的main函数，看到这个main函数是不是有种熟悉的感觉啊。在main函数中初始化了应用程序的主线程，同时初始化了主线程的消息队列，并调用了Looper.loop()函数使主线程不断的对消息队列进行循环检测，有消息则进行处理。点击事件产生一个消息，该消息传到InputEventReceiver后，由InputEventReceiver的继承类WindowInputEventReceiver去处理，WindowInputEventReceiver类是ViewRootImpl类的内部类，查看对应代码如下：

ViewRootImpl.java

final class WindowInputEventReceiver extends InputEventReceiver {
    public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
        super(inputChannel, looper);
    }

    @Override
    public void onInputEvent(InputEvent event) {
        enqueueInputEvent(event, this, 0, true);
    }

    @Override
    public void onBatchedInputEventPending() {
        if (mUnbufferedInputDispatch) {
            super.onBatchedInputEventPending();
        } else {
            scheduleConsumeBatchedInput();
        }
    }

    @Override
    public void dispose() {
        unscheduleConsumeBatchedInput();
        super.dispose();
    }
}

查看代码可以当点击消息过来时，直接调用ViewRootImpl类中的enqueueInputEvent(event,this,0,true)方法:

ViewRootImpl.java

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);

    if (processImmediately) {
        doProcessInputEvents();
    } else {
        scheduleProcessInputEvents();
    }
}

由于processImmediately为true，因而是立即处理，即直接调用doProcessInputEvents();

ViewRootImpl.java

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);

        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);
    }
}

z之后调用了deliverInputEvent(q)

ViewRootImpl.java

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) {
        stage.deliver(q);
    } else {
        finishInputEvent(q);
    }
}

在这里初始化了一个InputStage类的实例，然后调用了该类的deliver(q)，具体方法如下：

/**
     * Base class for implementing a stage in the chain of responsibility
     * for processing input events.
     * <p>
     * Events are delivered to the stage by the {@link #deliver} method.  The stage
     * then has the choice of finishing the event or forwarding it to the next stage.
     * </p>
     */
    abstract class InputStage {
        private final InputStage mNext;

        protected static final int FORWARD = 0;
        protected static final int FINISH_HANDLED = 1;
        protected static final int FINISH_NOT_HANDLED = 2;

        /**
         * Creates an input stage.
         * @param next The next stage to which events should be forwarded.
         */
        public InputStage(InputStage next) {
            mNext = next;
        }

        /**
         * Delivers an event to be processed.
         */
        public final void deliver(QueuedInputEvent q) {
            if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {
                forward(q);
            } else if (shouldDropInputEvent(q)) {
                finish(q, false);
            } else {
                apply(q, onProcess(q));
            }
        }

        /**
         * Marks the the input event as finished then forwards it to the next stage.
         */
        protected void finish(QueuedInputEvent q, boolean handled) {
            q.mFlags |= QueuedInputEvent.FLAG_FINISHED;
            if (handled) {
                q.mFlags |= QueuedInputEvent.FLAG_FINISHED_HANDLED;
            }
            forward(q);
        }

        /**
         * Forwards the event to the next stage.
         */
        protected void forward(QueuedInputEvent q) {
            onDeliverToNext(q);
        }

        /**
         * Applies a result code from {@link #onProcess} to the specified event.
         */
        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);
            }
        }

        /**
         * Called when an event is ready to be processed.
         * @return A result code indicating how the event was handled.
         */
        protected int onProcess(QueuedInputEvent q) {
            return FORWARD;
        }

        /**
         * Called when an event is being delivered to the next stage.
         */
        protected void onDeliverToNext(QueuedInputEvent q) {
            if (DEBUG_INPUT_STAGES) {
                Log.v(TAG, "Done with " + getClass().getSimpleName() + ". " + q);
            }
            if (mNext != null) {
                mNext.deliver(q);
            } else {
                finishInputEvent(q);
            }
        }

        protected boolean shouldDropInputEvent(QueuedInputEvent q) {
            if (mView == null || !mAdded) {
                Slog.w(TAG, "Dropping event due to root view being removed: " + q.mEvent);
                return true;
            } else if ((!mAttachInfo.mHasWindowFocus
                    && !q.mEvent.isFromSource(InputDevice.SOURCE_CLASS_POINTER)) || mStopped
                    || (mPausedForTransition && !isBack(q.mEvent))) {
                // This is a focus event and the window doesn't currently have input focus or
                // has stopped. This could be an event that came back from the previous stage
                // but the window has lost focus or stopped in the meantime.
                if (isTerminalInputEvent(q.mEvent)) {
                    // Don't drop terminal input events, however mark them as canceled.
                    q.mEvent.cancel();
                    Slog.w(TAG, "Cancelling event due to no window focus: " + q.mEvent);
                    return false;
                }

                // Drop non-terminal input events.
                Slog.w(TAG, "Dropping event due to no window focus: " + q.mEvent);
                return true;
            }
            return false;
        }

        void dump(String prefix, PrintWriter writer) {
            if (mNext != null) {
                mNext.dump(prefix, writer);
            }
        }

        private boolean isBack(InputEvent event) {
            if (event instanceof KeyEvent) {
                return ((KeyEvent) event).getKeyCode() == KeyEvent.KEYCODE_BACK;
            } else {
                return false;
            }
        }
    }

对应方法栈可以看出，进过一些列调用最终会调用到ViewPostImeInputStage类的processPointerEvent方法.

ViewRootImpl.java

private int processPointerEvent(QueuedInputEvent q) {
    final MotionEvent event = (MotionEvent)q.mEvent;

    mAttachInfo.mUnbufferedDispatchRequested = false;
    boolean handled = mView.dispatchPointerEvent(event);
    if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {
        mUnbufferedInputDispatch = true;
        if (mConsumeBatchedInputScheduled) {
            scheduleConsumeBatchedInputImmediately();
        }
    }
    return handled ? FINISH_HANDLED : FORWARD;
}

在该方法中调用了mView的dispatchPointerEvent，这个mView的初始化可以查看Activity的创建代码，在Activity创建的时候会给Activity设置一个根布局也就是DecorView，这里的mView就是DecorView，这个DecorView是PhoneWindow的私有内部类，它继承于FrameLayout并实现了RootViewSurfaceTaker接口，但是该方法是View类的一个final方法，子类无法覆写，直接查看View中的相应代码即可。代码如下：

View.java

/**
 * 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()) {
        return dispatchTouchEvent(event);
    } else {
        return dispatchGenericMotionEvent(event);
    }
}

继续查看DecorView类中的dispatchTouchEvent方法，代码如下：

PhoneWindow.java

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

这个getCallback也就是当前的Activity，当当前Activity没有destroy的时候即调用该Activity的dispatchTouchEvent，这里代码就回到了应用层了，框架层完成了很多操作，这些操作只有查看源码才知道，这里终于回到了我们编写代码的地方了。当然这之后还是会通过框架层将对应的Touch事件传给对应的ViewGroup和View。下面先看下Activity中dispatchTouchEvent的代码：

Activity.java

/**
 * Called to process touch screen events.  You can override this to
 * intercept all touch screen events before they are dispatched to the
 * window.  Be sure to call this implementation for touch screen events
 * that should be handled normally.
 *
 * @param ev The touch screen event.
 *
 * @return boolean Return true if this event was consumed.
 */
public boolean dispatchTouchEvent(MotionEvent ev) {
    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        onUserInteraction();
    }
    if (getWindow().superDispatchTouchEvent(ev)) {//这个getWindow就是PhoneWindow，也就是通过PhoneWindow继续对touch事件进行分发。
        return true;
    }//当上面返回true，也就是View把事件消费了，那么就不再调用Activity的onTouchEvent函数了。
    return onTouchEvent(ev);
}

果然这里又回到了框架层，这里getWindow就是PhoneWindow，继续查看PhoneWindow的代码：

PhoneWindow.java

@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
    return mDecor.superDispatchTouchEvent(event);
}

这里把事件就传给了DecorView进行分发。

PhoneWindow.java->DecorView

public boolean superDispatchTouchEvent(MotionEvent event) {
    return super.dispatchTouchEvent(event);
}

前面说过DecorView继承于FrameLayout，这里super.dispatchTouchEvent就是调用了FrameLayout里面的dispatchTouchEvent，而FrameLayout类中并未重写dispatchTouchEvent，因而直接调用的是ViewGroup中的dispatchTouchEvent。继续查看代码：

ViewGroup.java

/**
 * {@inheritDoc}
 */
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    if (mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
    }

    // If the event targets the accessibility focused view and this is it, start
    // normal event dispatch. Maybe a descendant is what will handle the click.
    if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
        ev.setTargetAccessibilityFocus(false);
    }

    boolean handled = false;
    if (onFilterTouchEventForSecurity(ev)) {
        final int action = ev.getAction();
        final int actionMasked = action & MotionEvent.ACTION_MASK;

        // Handle an initial down.
        if (actionMasked == MotionEvent.ACTION_DOWN) {
            // Throw away all previous state when starting a new touch gesture.
            // The framework may have dropped the up or cancel event for the previous gesture
            // due to an app switch, ANR, or some other state change.
            cancelAndClearTouchTargets(ev);
            resetTouchState();
        }

        // Check for interception.
        final boolean intercepted;
        if (actionMasked == MotionEvent.ACTION_DOWN
                || mFirstTouchTarget != null) {
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
            if (!disallowIntercept) {
                intercepted = onInterceptTouchEvent(ev);
                ev.setAction(action); // restore action in case it was changed
            } else {
                intercepted = false;
            }
        } else {
            // There are no touch targets and this action is not an initial down
            // so this view group continues to intercept touches.
            intercepted = true;
        }

        // If intercepted, start normal event dispatch. Also if there is already
        // a view that is handling the gesture, do normal event dispatch.
        if (intercepted || mFirstTouchTarget != null) {
            ev.setTargetAccessibilityFocus(false);
        }

        // Check for cancelation.
        final boolean canceled = resetCancelNextUpFlag(this)
                || actionMasked == MotionEvent.ACTION_CANCEL;

        // Update list of touch targets for pointer down, if needed.
        final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
        TouchTarget newTouchTarget = null;
        boolean alreadyDispatchedToNewTouchTarget = false;
        if (!canceled && !intercepted) {

            // If the event is targeting accessiiblity focus we give it to the
            // view that has accessibility focus and if it does not handle it
            // we clear the flag and dispatch the event to all children as usual.
            // We are looking up the accessibility focused host to avoid keeping
            // state since these events are very rare.
            View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
                    ? findChildWithAccessibilityFocus() : null;

            if (actionMasked == MotionEvent.ACTION_DOWN
                    || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                    || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                final int actionIndex = ev.getActionIndex(); // always 0 for down
                final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                        : TouchTarget.ALL_POINTER_IDS;

                // Clean up earlier touch targets for this pointer id in case they
                // have become out of sync.
                removePointersFromTouchTargets(idBitsToAssign);

                final int childrenCount = mChildrenCount;
                if (newTouchTarget == null && childrenCount != 0) {
                    final float x = ev.getX(actionIndex);
                    final float y = ev.getY(actionIndex);
                    // Find a child that can receive the event.
                    // Scan children from front to back.
                    final ArrayList<View> preorderedList = buildOrderedChildList();
                    final boolean customOrder = preorderedList == null
                            && isChildrenDrawingOrderEnabled();
                    final View[] children = mChildren;
                    for (int i = childrenCount - 1; i >= 0; i--) {
                        final int childIndex = customOrder
                                ? getChildDrawingOrder(childrenCount, i) : i;
                        final View child = (preorderedList == null)
                                ? children[childIndex] : preorderedList.get(childIndex);

                        // If there is a view that has accessibility focus we want it
                        // to get the event first and if not handled we will perform a
                        // normal dispatch. We may do a double iteration but this is
                        // safer given the timeframe.
                        if (childWithAccessibilityFocus != null) {
                            if (childWithAccessibilityFocus != child) {
                                continue;
                            }
                            childWithAccessibilityFocus = null;
                            i = childrenCount - 1;
                        }

                        if (!canViewReceivePointerEvents(child)
                                || !isTransformedTouchPointInView(x, y, child, null)) {
                            ev.setTargetAccessibilityFocus(false);
                            continue;
                        }

                        newTouchTarget = getTouchTarget(child);
                        if (newTouchTarget != null) {
                            // Child is already receiving touch within its bounds.
                            // Give it the new pointer in addition to the ones it is handling.
                            newTouchTarget.pointerIdBits |= idBitsToAssign;
                            break;
                        }

                        resetCancelNextUpFlag(child);
                        if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                            // Child wants to receive touch within its bounds.
                            mLastTouchDownTime = ev.getDownTime();
                            if (preorderedList != null) {
                                // childIndex points into presorted list, find original index
                                for (int j = 0; j < childrenCount; j++) {
                                    if (children[childIndex] == mChildren[j]) {
                                        mLastTouchDownIndex = j;
                                        break;
                                    }
                                }
                            } else {
                                mLastTouchDownIndex = childIndex;
                            }
                            mLastTouchDownX = ev.getX();
                            mLastTouchDownY = ev.getY();
                            newTouchTarget = addTouchTarget(child, idBitsToAssign);
                            alreadyDispatchedToNewTouchTarget = true;
                            break;
                        }

                        // The accessibility focus didn't handle the event, so clear
                        // the flag and do a normal dispatch to all children.
                        ev.setTargetAccessibilityFocus(false);
                    }
                    if (preorderedList != null) preorderedList.clear();
                }

                if (newTouchTarget == null && mFirstTouchTarget != null) {
                    // Did not find a child to receive the event.
                    // Assign the pointer to the least recently added target.
                    newTouchTarget = mFirstTouchTarget;
                    while (newTouchTarget.next != null) {
                        newTouchTarget = newTouchTarget.next;
                    }
                    newTouchTarget.pointerIdBits |= idBitsToAssign;
                }
            }
        }

        // Dispatch to touch targets.
        if (mFirstTouchTarget == null) {
            // No touch targets so treat this as an ordinary view.
            handled = dispatchTransformedTouchEvent(ev, canceled, null,
                    TouchTarget.ALL_POINTER_IDS);
        } else {
            // Dispatch to touch targets, excluding the new touch target if we already
            // dispatched to it.  Cancel touch targets if necessary.
            TouchTarget predecessor = null;
            TouchTarget target = mFirstTouchTarget;
            while (target != null) {
                final TouchTarget next = target.next;
                if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                    handled = true;
                } else {
                    final boolean cancelChild = resetCancelNextUpFlag(target.child)
                            || intercepted;
                    if (dispatchTransformedTouchEvent(ev, cancelChild,
                            target.child, target.pointerIdBits)) {
                        handled = true;
                    }
                    if (cancelChild) {
                        if (predecessor == null) {
                            mFirstTouchTarget = next;
                        } else {
                            predecessor.next = next;
                        }
                        target.recycle();
                        target = next;
                        continue;
                    }
                }
                predecessor = target;
                target = next;
            }
        }

        // Update list of touch targets for pointer up or cancel, if needed.
        if (canceled
                || actionMasked == MotionEvent.ACTION_UP
                || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
            resetTouchState();
        } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
            final int actionIndex = ev.getActionIndex();
            final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
            removePointersFromTouchTargets(idBitsToRemove);
        }
    }

    if (!handled && mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
    }
    return handled;
}

代码有点多，通过调试可知将会调用dispatchTransformedTouchEvent，查看代码如下：

ViewGroup.java

/**
 * Transforms a motion event into the coordinate space of a particular child view,
 * filters out irrelevant pointer ids, and overrides its action if necessary.
 * If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
 */
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
        View child, int desiredPointerIdBits) {
    final boolean handled;

    // Canceling motions is a special case.  We don't need to perform any transformations
    // or filtering.  The important part is the action, not the contents.
    final int oldAction = event.getAction();
    if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
        event.setAction(MotionEvent.ACTION_CANCEL);
        if (child == null) {
            handled = super.dispatchTouchEvent(event);
        } else {
            handled = child.dispatchTouchEvent(event);
        }
        event.setAction(oldAction);
        return handled;
    }

    // Calculate the number of pointers to deliver.
    final int oldPointerIdBits = event.getPointerIdBits();
    final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;

    // If for some reason we ended up in an inconsistent state where it looks like we
    // might produce a motion event with no pointers in it, then drop the event.
    if (newPointerIdBits == 0) {
        return false;
    }

    // If the number of pointers is the same and we don't need to perform any fancy
    // irreversible transformations, then we can reuse the motion event for this
    // dispatch as long as we are careful to revert any changes we make.
    // Otherwise we need to make a copy.
    final MotionEvent transformedEvent;
    if (newPointerIdBits == oldPointerIdBits) {
        if (child == null || child.hasIdentityMatrix()) {
            if (child == null) {
                handled = super.dispatchTouchEvent(event);
            } else {
                final float offsetX = mScrollX - child.mLeft;
                final float offsetY = mScrollY - child.mTop;
                event.offsetLocation(offsetX, offsetY);

                handled = child.dispatchTouchEvent(event);

                event.offsetLocation(-offsetX, -offsetY);
            }
            return handled;
        }
        transformedEvent = MotionEvent.obtain(event);
    } else {
        transformedEvent = event.split(newPointerIdBits);
    }

    // Perform any necessary transformations and dispatch.
    if (child == null) {
        handled = super.dispatchTouchEvent(transformedEvent);
    } else {
        final float offsetX = mScrollX - child.mLeft;
        final float offsetY = mScrollY - child.mTop;
        transformedEvent.offsetLocation(offsetX, offsetY);
        if (! child.hasIdentityMatrix()) {
            transformedEvent.transform(child.getInverseMatrix());
        }

        handled = child.dispatchTouchEvent(transformedEvent);
    }

    // Done.
    transformedEvent.recycle();
    return handled;
}

在该函数中调用了child.dispatchTouchEvent()，这里便走到了子View的dispatchTouchEvent中。子View也就是MyView，也就走到了TextView的dispathTouchEvent中，由于TextView并未重写dispathTouchEvent，因而直接进入View的dispatchTouchEvent中，代码如下：

View.java

/**
 * Pass the touch screen motion event down to the target view, or this
 * view if it is the target.
 *
 * @param event The motion event to be dispatched.
 * @return True if the event was handled by the view, false otherwise.
 */
public boolean dispatchTouchEvent(MotionEvent event) {
    // If the event should be handled by accessibility focus first.
    if (event.isTargetAccessibilityFocus()) {
        // We don't have focus or no virtual descendant has it, do not handle the event.
        if (!isAccessibilityFocusedViewOrHost()) {
            return false;
        }
        // We have focus and got the event, then use normal event dispatch.
        event.setTargetAccessibilityFocus(false);
    }

    boolean result = false;

    if (mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onTouchEvent(event, 0);
    }

    final int actionMasked = event.getActionMasked();
    if (actionMasked == MotionEvent.ACTION_DOWN) {
        // Defensive cleanup for new gesture
        stopNestedScroll();
    }

    if (onFilterTouchEventForSecurity(event)) {
        //noinspection SimplifiableIfStatement
        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnTouchListener != null
                && (mViewFlags & ENABLED_MASK) == ENABLED
                && li.mOnTouchListener.onTouch(this, event)) {//在这里就调用了setOnTouchListener中的onTouch函数，如果有一个消费了，那么result=true
            result = true;
        }

        if (!result && onTouchEvent(event)) {//当上面的result为true时，子View的onTouchEvent便不会执行了。
            result = true;
        }
    }

    if (!result && mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
    }

    // Clean up after nested scrolls if this is the end of a gesture;
    // also cancel it if we tried an ACTION_DOWN but we didn't want the rest
    // of the gesture.
    if (actionMasked == MotionEvent.ACTION_UP ||
            actionMasked == MotionEvent.ACTION_CANCEL ||
            (actionMasked == MotionEvent.ACTION_DOWN && !result)) {
        stopNestedScroll();
    }

    return result;
}

在该函数中看到了在MainActivity中设置的setOnTouchListener对应的Listener接口，当setListener中的onTouch返回true时，MyView本身的onTouchEvent便不被调用。接下来看下View的onTouchEvent代码：

View.java

public boolean onTouchEvent(MotionEvent event) {
        final float x = event.getX();
        final float y = event.getY();
        final int viewFlags = mViewFlags;
        final int action = event.getAction();

        if ((viewFlags & ENABLED_MASK) == DISABLED) {
            if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
                setPressed(false);
            }
            // A disabled view that is clickable still consumes the touch
            // events, it just doesn't respond to them.
            return (((viewFlags & CLICKABLE) == CLICKABLE
                    || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                    || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
        }

        if (mTouchDelegate != null) {//一个View还可以设置TouchDelegate，也可以在TouchDelegate的onTouchEvent里面处理点击事件
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }

        if (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
                (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                    boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                    if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                        // take focus if we don't have it already and we should in
                        // touch mode.
                        boolean focusTaken = false;
                        if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                            focusTaken = requestFocus();
                        }

                        if (prepressed) {
                            // The button is being released before we actually
                            // showed it as pressed.  Make it show the pressed
                            // state now (before scheduling the click) to ensure
                            // the user sees it.
                            setPressed(true, x, y);
                       }

                        if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                            // This is a tap, so remove the longpress check
                            removeLongPressCallback();

                            // Only perform take click actions if we were in the pressed state
                            if (!focusTaken) {
                                // Use a Runnable and post this rather than calling
                                // performClick directly. This lets other visual state
                                // of the view update before click actions start.
                                if (mPerformClick == null) {
                                    mPerformClick = new PerformClick();
                                }
                                if (!post(mPerformClick)) {
                                    performClick();
                                }
                            }
                        }

                        if (mUnsetPressedState == null) {
                            mUnsetPressedState = new UnsetPressedState();
                        }

                        if (prepressed) {
                            postDelayed(mUnsetPressedState,
                                    ViewConfiguration.getPressedStateDuration());
                        } else if (!post(mUnsetPressedState)) {
                            // If the post failed, unpress right now
                            mUnsetPressedState.run();
                        }

                        removeTapCallback();
                    }
                    mIgnoreNextUpEvent = false;
                    break;

                case MotionEvent.ACTION_DOWN:
                    mHasPerformedLongPress = false;

                    if (performButtonActionOnTouchDown(event)) {
                        break;
                    }

                    // Walk up the hierarchy to determine if we're inside a scrolling container.
                    boolean isInScrollingContainer = isInScrollingContainer();

                    // For views inside a scrolling container, delay the pressed feedback for
                    // a short period in case this is a scroll.
                    if (isInScrollingContainer) {
                        mPrivateFlags |= PFLAG_PREPRESSED;
                        if (mPendingCheckForTap == null) {
                            mPendingCheckForTap = new CheckForTap();
                        }
                        mPendingCheckForTap.x = event.getX();
                        mPendingCheckForTap.y = event.getY();

//这个注意下，这里会调用ViewRootImpl内部函数也就是后面的MOVE为啥知道前面DOWN了

postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout()); } else { // Not inside a scrolling container, so show the feedback right away setPressed(true, x, y);

//这个去检查是否有长按事件

checkForLongClick(0); } break; case MotionEvent.ACTION_CANCEL: setPressed(false); removeTapCallback(); removeLongPressCallback(); mInContextButtonPress = false; mHasPerformedLongPress = false; mIgnoreNextUpEvent = false; break; case MotionEvent.ACTION_MOVE: drawableHotspotChanged(x, y); // Be lenient about moving outside of buttons if (!pointInView(x, y, mTouchSlop)) { // Outside button removeTapCallback(); if ((mPrivateFlags & PFLAG_PRESSED) != 0) { // Remove any future long press/tap checks removeLongPressCallback(); setPressed(false); } } break; } return true; } return false; }这里仅分析下DOWN事件的处理，这里会先处理按钮自身的一些事件，具体事件见如下代码：

/**
 * Performs button-related actions during a touch down event.
 *
 * @param event The event.
 * @return True if the down was consumed.
 *
 * @hide
 */
protected boolean performButtonActionOnTouchDown(MotionEvent event) {
    if (event.getToolType(0) == MotionEvent.TOOL_TYPE_MOUSE &&
        (event.getButtonState() & MotionEvent.BUTTON_SECONDARY) != 0) {
        showContextMenu(event.getX(), event.getY(), event.getMetaState());
        mPrivateFlags |= PFLAG_CANCEL_NEXT_UP_EVENT;
        return true;
    }
    return false;
}

然后判断当前View的父View是否在滚动，如果不在滚动就调用postDelayed：

View.java

public boolean postDelayed(Runnable action, long delayMillis) {
    final AttachInfo attachInfo = mAttachInfo;
    if (attachInfo != null) {
        return attachInfo.mHandler.postDelayed(action, delayMillis);
    }
    // Assume that post will succeed later
    ViewRootImpl.getRunQueue().postDelayed(action, delayMillis);
    return true;
}

将action延迟一段时间，用于后续判断（是否长按事件，后续MOVE事件，UP事件）。