Android中onInterceptTouchEvent、dispatchTouchEvent及onTouchEvent的调用顺序及内部原理详解
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。
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.
*
* 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. *
*/ 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.
*
* 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. *
* * @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 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）。
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