Android事件分发机制浅析

事件机制是Android中一个比较复杂且重要的知识点，比如你想自定义拦截事件，或者某系组件中嵌套了其他布局，往往会出现这样那样的事件冲突，坑爹啊！！事件主要涵盖onTouch，onClick，onTouchEvent，dispatchTouchEvent，onInterceptTouchEvent等等一系列事件，并且事件间还相互交互耦合，甚至有的事件还有返回值，一会true，一会false，什么情况下返回true，什么情况下返回false，为什么要有返回值，想想这些就感觉整个人都不好了。



但是（万恶的但是），该知识点还是必须要掌握的，知识的深度与广度决定了你走的远度，鉴于此我们就来捅一捅该知识点。

准备工作

俗话说工欲善其事必先利其器，为了看他的执行流程，我们还是先写个样例，打几个日志看看执行流程吧！

首先自定义一个外层布局的Layout，自定义Layout继承了LinearLayout，复写了相应的函数，在调用之前输入日志。如下：

public class Layout extends LinearLayout {
public Layout(Context context) {
super(context);
init();
}

public Layout(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}

public Layout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}

private void init() {
//requestDisallowInterceptTouchEvent(false);
}

@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.e("Event", "Layout onInterceptTouchEvent " + MotionEvent.actionToString(ev.getAction()));
return super.onInterceptTouchEvent(ev);
}

@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e("Event", "Layout onTouchEvent " + MotionEvent.actionToString(event.getAction()));
return super.onTouchEvent(event);
}

@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.e("Event", "Layout dispatchTouchEvent " + MotionEvent.actionToString(event.getAction()));
return super.dispatchTouchEvent(event);
}

}

我们还自定义了一个LogTextView，继承自TextView，也是为了输出日志，代码如下：

public class LogTextView extends TextView {

public LogTextView(Context context) {
super(context);
}

public LogTextView(Context context, AttributeSet attrs) {
super(context, attrs);
}

public LogTextView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}

@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e("Event", "TextView  onTouchEvent " + MotionEvent.actionToString(event.getAction()));
return super.onTouchEvent(event);
}

@Override
public void setOnTouchListener(OnTouchListener l) {
super.setOnTouchListener(l);
}

@Override
public void setOnClickListener(OnClickListener l) {
super.setOnClickListener(l);
}
}

接下来是布局文件了：

<?xml version="1.0" encoding="utf-8"?>
<com.sunny.event.wigdet.Layout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin">

<com.sunny.event.wigdet.LogTextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="40dp"
android:background="#999999"
android:padding="20dp"
android:text="Hello World!"/>

<ImageView
android:id="@+id/image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="20dp"
android:src="@mipmap/ic_launcher"/>
</com.sunny.event.wigdet.Layout>

布局中嵌套了两个view，一个TextView，一个ImageView。最后就是主界面了。

public class MainActivity extends AppCompatActivity {

private LogTextView tv;
private ImageView imageView;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViews();
setViewListener();
}

private void findViews() {
tv = (LogTextView) findViewById(R.id.textView);
imageView = (ImageView) findViewById(R.id.image);
}

private void setViewListener() {
tv.setOnTouchListener(new View.OnTouchListener() {
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e("Event", "TextView  onTouch " + MotionEvent.actionToString(event.getAction()));
return true;
}
});
tv.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e("Event", "TextView  onClick ");
}
});
imageView.setOnTouchListener(new View.OnTouchListener() {
@TargetApi(Build.VERSION_CODES.KITKAT)
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e("Event", "ImageView onTouch " + MotionEvent.actionToString(event.getAction()));
return false;
}
});
imageView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e("Event", "ImageView onClick ");
}
});
}
}

执行结果

round 1

TextView的onTouch返回为false，点击TextView，日志如下：

05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_DOWN
05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_DOWN
05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: TextView  onTouch ACTION_DOWN
05-05 14:04:44.091 27644-27644/com.sunny.event E/Event: TextView  onTouchEvent ACTION_DOWN
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: TextView  onTouch ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: TextView  onTouchEvent ACTION_MOVE
05-05 14:04:44.158 27644-27644/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: TextView  onTouch ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: TextView  onTouchEvent ACTION_UP
05-05 14:04:44.159 27644-27644/com.sunny.event E/Event: TextView  onClick

根据日志我们可以看到首先有一个ACTION_DOWN事件，执行的顺序是Layout的dispatchTouchEvent→onInterceptTouchEvent→（TextView）onTouch要→onTouchEvent，之后的我帕金森发生了，产生了ACTION_MOVE事件，传递的顺序与Down是一致的，最后一个事件是UP事件，正常点击不滑动是不会产生MOVE事件的，在这个这个三个事件最后调用了TextView的onClick事件。

小结：

1 . 事件的传递顺序是先外层容器，之后再是具体的View。

2. onTouch事件先于onTouchEvent事件，onTouchEvent先于onClick事件

round 2

我们将TextView的onTouch事件返回true。重新执行。执行顺序如下：

05-05 14:10:20.556 27644-27644/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_DOWN
05-05 14:10:20.556 27644-27644/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_DOWN
05-05 14:10:20.556 27644-27644/com.sunny.event E/Event: TextView  onTouch ACTION_DOWN
05-05 14:10:20.616 27644-27644/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_MOVE
05-05 14:10:20.616 27644-27644/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_MOVE
05-05 14:10:20.616 27644-27644/com.sunny.event E/Event: TextView  onTouch ACTION_MOVE
05-05 14:10:20.622 27644-27644/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_UP
05-05 14:10:20.622 27644-27644/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_UP
05-05 14:10:20.622 27644-27644/com.sunny.event E/Event: TextView  onTouch ACTION_UP

从日志可以看出如果onTouch返回为true，执行顺序变成了如下：

首先还是ACTION_DOWN事件（Layout）dispatchTouchEvent→onInterceptTouchEvent→（TextView）onTouch，ACTION_MOVE与ACTION_UP执行顺序同ACTION_DOWN，可以发现的是TextView的onTouchEvent事件没有了，并且onClick事件也没有了。

小结

1，onTouch事件的返回值为true会拦截onTouchEvent事件

2，onTouchEvent与onClick有关联

上面的两次执行中每次都调用了onInterceptTouchEvent事件，这个到底又是啥？我们去看看他的返回值是什么？

public boolean onInterceptTouchEvent(MotionEvent ev) {
return false;
}

可以看到默认返回false，注释长的吓人，那我们就来改写一下他的返回值，这个函数是ViewGroup才有的，说明与布局容器有关.

round 3

我们将Layout的onInterceptTouchEvent的返回值改为true。重新执行。执行顺序如下：

05-05 14:59:17.829 15157-15157/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_DOWN
05-05 14:59:17.830 15157-15157/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_DOWN
05-05 14:59:17.830 15157-15157/com.sunny.event E/Event: Layout    onTouchEvent ACTION_DOWN

从日志可以发现，只有最外层的控件能够执行事件，TextView已经收不到任何事件。

小结

父控件onInterceptTouchEvent返回true会拦截子控件的事件

追根溯源

我们从代码的层面来看看他是怎么执行的，当屏幕接收到点击事件时会首先传递到Activity的dispatchTouchEvent：

/**
* 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)) {
return true;
}
return onTouchEvent(ev);
}

在这里执行了三步，

1.第一告诉用户ACTION_DOWN，用户可以复写onUserInteraction来处理点击开始

2.调用了getWindow().superDispatchTouchEvent(ev)，这里的getWindow得到是PhoneWindow对象，因此执行的PhoneWindow的superDispatchTouchEvent函数，

3.调用了Activity的onTouchEvent事件

PhoneWindow的superDispatchTouchEvent又调用了DecorView的superDispatchTouchEvent函数，每一个Activity都有一个PhoneWindow，每一个PhoneWindow都有一个DecorView，DecoView继承自FrameLayout，这里又调用了super.dispatchTouchEvent(event)，FrameLayout里面是没有改函数的，所以最终执行的是ViewGroup的dispatchTouchEvent函数。

这里我们先穿插一点界面的知识，以我测试手机为例，DecorView中有两个child，分别是ViewStub和LinerLayout，LinerLayout中又包含了FrameLayout，FrameLayout中包含了一个ActionBarOverlayLayout，ActionBarOverlayLayout里又包含了两个child，分别是ActionBarContainer与ContentFrameLayout。

接下来我们去看看ViewGroup的dispatchTouchEvent函数：

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
.........
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) {
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;
}
............
// 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 (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 (!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;
}
}
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;
}

我们只看最重要的部分

1： 事件为ACTION_DOWN时，执行了cancelAndClearTouchTargets函数，该函数主要清除上一次点击传递的路径，之后执行了resetTouchState，重置了touch状态，其中执行了 mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;就是拦截状态为false，这个与requestDisallowInterceptTouchEvent函数相关。

2： 获取intercepted的值，首先判断了disallowIntercept状态，是否拦截子控件的事件执行。从代码可以看到当disallowIntercept为false时，该状态主要取决于onInterceptTouchEvent函数的返回值，这就是前面我们拦截的函数，如果为true，这时intercepted为true标识拦截。

3： 接着判断了!canceled && !intercepted的值，canceled这里为false，如果intercepted为false，则会进入判断条件，这里假设不拦截，进入后继续判断如果是ACTION_DOWN事件，则会继续进入判断，遍历所有子控件，isTransformedTouchPointInView会判断当前点击区域是否在控件内，如果不在则遍历下一个，之后调用dispatchTransformedTouchEvent函数。最后在调用addTouchTarget函数，将当前选中的控件，挂载到当前点击目标链表。alreadyDispatchedToNewTouchTarget赋值为true。

接着判断mFirstTouchTarget是否为空，经过上一步的addTouchTarget的执行，这里mFirstTouchTarget不为空。第一个事件alreadyDispatchedToNewTouchTarget为true，且target == newTouchTarget，因此handled值为true，如果是后续的事件，则会进入dispatchTransformedTouchEvent中。

我们接着看看第三部中的dispatchTransformedTouchEvent函数：

private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;

// Calculate the number of pointers to deliver.
final int oldPointerIdBits = event.getPointerIdBits();
final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
.......
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);
}
.......
// Done.
transformedEvent.recycle();
return handled;
}

这里会进入到第10行，且传递过来的child不为空，因此会继续执行child.dispatchTouchEvent，这里继续执行ViewGroup的dispatchTouchEvent，一直递归执行，直到真正接受点击的控件，到最后child会为空，这里要么是一个View控件，要么是未包含任何子控件的ViewGroup，这时这里会执行View的dispatchTouchEvent。

从上述执行逻辑可以直到，先从DecorView一直递归到Layout，最后再到TextView，这里我们去看看View的dispatchTouchEvent：

public boolean dispatchTouchEvent(MotionEvent event) {

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)) {
result = true;
}

if (!result && onTouchEvent(event)) {
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;
}

首先会停止掉嵌套滑动，之后先判断了ListenerInfo不为空，这里只要是设置了onTouch，onKey，onHover，onDrag等等中的任何一个这里就不为空，具体可以去看看ListenerInfo包含的listenerInfo类型。其次判断了mOnTouchListener不为空，只要设置了onTouchListener这里就不为空，再之后判断了该控件是否是enabled，一般都会enabled，可以代码设置为false，再之后调用了mOnTouchListener的onTouch事件，这里就是外面传进来的onTouchListener，从这里可以看到无论onTouch返回任何值，onTouch事件都会执行，但是如果返回为true，则会导致result为true，!result && onTouchEvent(event)因为短路，不会执行到onTouchEvent事件。

小结

1：onTouch返回为true导致onTouchEvent不能执行

2：如果enable为false，因为短路onTouch不会执行

到此还没有看到任何onClick事件的执行，我们继续去看看onTouchEvent函数：

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

我们首先看ACTION_DOWN事件，这里主要看checkForLongClick，CheckForTap中也调用了该函数，这里就是添加一个长按事件，如果达到长按标准且长按listener不为空，则执行长按事件，接着我们看ACTION_UP，这里看到如果不是长按事件，则调用了performClick，performClick里面执行了onClick事件。

小结

1：onClick事件与onLongClick事件是在onTouchEvent中执行的

2：如果执行了长按事件则onClick不执行

3：就api 23代码，长按的时间间隔为500毫秒

上面解析了intercepted为false的情况，那intercepted为true，它到底是怎么拦截的？

如果intercepted为true，则!canceled && !intercepted为false，不能进入该判断，mFirstTouchTarget为空，会继续执行如下分支：

if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
}

这里第三参数传递的child为null，因此就会执行该控件onTouch与onTouchEvent函数，不会继续递归传递，因此也就拦截了子控件的执行。

总结

事件接收先从父控件到子控件，如果父控件onInterceptTouchEvent为true，则表示拦截事件。

dispatchTouchEvent的ACTION_DOWN事件中，会清除上一次的点击目标列表，且重置disallowIntercept状态为false，表示拦截，但是真正的拦截状态还是靠onInterceptTouchEvent函数的返回值决定。

如果为自定义控件，自定义控件与父控件有事件冲突，比如说滑动等，还需要重写onInterceptTouchEvent。

如果onLongClick执行，api 23 默认时间为500毫秒，则onClick不执行。

如果onTouch事件返回为true，则会拦截onTouchEvent事件，onClick，onLongClick事件均不在执行。