在分析Android事件分发机制前，明确android的两大基础控件类型:View和ViewGroup。View即普通的控件，没有子布局的，如Button、TextView. ViewGroup继承自View，表示可以有子控件，如Linearlayout、Listview这些。今天我们先来了解View的事件分发机制。
先看下代码，非常简单，只有一个Button，分别给它注册了OnClick和OnTouch的点击事件。
1 btn.setOnClickListener(new View.OnClickListener() {
2 @Override
3 public void onClick(View v) {
4 Log.i("Tag", "This is button onClick event");
5 }
6 });
7 btn.setOnTouchListener(new View.OnTouchListener() {
8 @Override
9 public boolean onTouch(View v, MotionEvent event) {
10 Log.i("Tag", "This is button onTouch action" + event.getAction());
11 return false;
12 }
13 });
运行一下项目，结果如下：
1 I/Tag: This is button onTouch action0 2 I/Tag: This is button onTouch action2 3 I/Tag: This is button onTouch action2 4 I/Tag: This is button onTouch action1 5 I/Tag: This is button onClick event
可以看到，onTouch是有先于onClick执行的，因此事件的传递顺序是先onTouch，在到OnClick。具体为什么这样，下面会通过源码来说明。这时，我们可能注意到了，onTouch的方法是有返回值，这里是返回false，我们将它改为true再运行一次，结果如下：
1 I/Tag: This is button onTouch action0 2 I/Tag: This is button onTouch action2 3 I/Tag: This is button onTouch action2 4 I/Tag: This is button onTouch action2 5 I/Tag: This is button onTouch action1
对比两次结果，我们发现onClick方法不再执行，为什么会这样，下面我将通过源码给大家一步步理清这个思路。
查看源码时，首先要知道所有View类型控件事件入口都是dispatchTouchEvent()，所以我们直接进入到View这个类里面的dispatchTouchEvent（）方法看一下。
1 public boolean dispatchTouchEvent(MotionEvent event) {
2 // If the event should be handled by accessibility focus first.
3 if (event.isTargetAccessibilityFocus()) {
4 // We don‘t have focus or no virtual descendant has it, do not handle the event.
5 if (!isAccessibilityFocusedViewOrHost()) {
6 return false;
7 }
8 // We have focus and got the event, then use normal event dispatch.
9 event.setTargetAccessibilityFocus(false);
10 }
11 boolean result = false;
12 if (mInputEventConsistencyVerifier != null) {
13 mInputEventConsistencyVerifier.onTouchEvent(event, 0);
14 }
15 final int actionMasked = event.getActionMasked();
16 if (actionMasked == MotionEvent.ACTION_DOWN) {
17 // Defensive cleanup for new gesture
18 stopNestedScroll();
19 }
20 if (onFilterTouchEventForSecurity(event)) {
21 //noinspection SimplifiableIfStatement
22 ListenerInfo li = mListenerInfo;
23 if (li != null && li.mOnTouchListener != null
24 && (mViewFlags & ENABLED_MASK) == ENABLED
25 && li.mOnTouchListener.onTouch(this, event)) {
26 result = true;
27 }
28 if (!result && onTouchEvent(event)) {
29 result = true;
30 }
31 }
32 if (!result && mInputEventConsistencyVerifier != null) {
33 mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
34 }
35 // Clean up after nested scrolls if this is the end of a gesture;
36 // also cancel it if we tried an ACTION_DOWN but we didn‘t want the rest
37 // of the gesture.
38 if (actionMasked == MotionEvent.ACTION_UP ||
39 actionMasked == MotionEvent.ACTION_CANCEL ||
40 (actionMasked == MotionEvent.ACTION_DOWN && !result)) {
41 stopNestedScroll();
42 }
43 return result;
44 }
从源码第25行处可以看到，mOnTouchListener.onTouch()的方法首先被执行，如果li != null && li.mOnTouchListener != null&& (mViewFlags & ENABLED_MASK) == ENABLED&& li.mOnTouchListener.onTouch(this, event)都为真的话，result赋值为true，否则就执行onTouchEvent(event)方法。
从上面可以看到要符合条件有四个，
1、ListenerInfo li，它是view中的一个静态类，里面定义view的事件的监听等等，所以有涉及到view的事件，ListenerInfo都会被实例化，因此li不为null
2、mOnTouchiListener是在setOnTouchListener方法里面赋值的，只要touch事件被注册，mOnTouchiListener一定不会null
3、 (mViewFlags & ENABLED_MASK) == ENABLED，是判断当前点击的控件是否是enable的，button默认为enable，这个条件也恒定为true，
4、重点来了，li.mOnTouchListener.onTouch(this, event)就是回调控件onTouch方法，当这个条件也为true时，result=true,onTouchEvent（event）将不会被执行。如果onTouch返回false，就会再执行onTouchEvent(event)方法。
我们接着再进入到onTouchEvent方法查看源码。
1 public boolean onTouchEvent(MotionEvent event) {
2 final float x = event.getX();
3 final float y = event.getY();
4 final int viewFlags = mViewFlags;
5 final int action = event.getAction();
6 if ((viewFlags & ENABLED_MASK) == DISABLED) {
7 if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
8 setPressed(false);
9 }
10 // A disabled view that is clickable still consumes the touch
11 // events, it just doesn‘t respond to them.
12 return (((viewFlags & CLICKABLE) == CLICKABLE
13 || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
14 || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
15 }
16 if (mTouchDelegate != null) {
17 if (mTouchDelegate.onTouchEvent(event)) {
18 return true;
19 }
20 }
21 if (((viewFlags & CLICKABLE) == CLICKABLE ||
22 (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
23 (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
24 switch (action) {
25 case MotionEvent.ACTION_UP:
26 boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
27 if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
28 // take focus if we don‘t have it already and we should in
29 // touch mode.
30 boolean focusTaken = false;
31 if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
32 focusTaken = requestFocus();
33 }
34 if (prepressed) {
35 // The button is being released before we actually
36 // showed it as pressed. Make it show the pressed
37 // state now (before scheduling the click) to ensure
38 // the user sees it.
39 setPressed(true, x, y);
40 }
41 if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
42 // This is a tap, so remove the longpress check
43 removeLongPressCallback();
44 // Only perform take click actions if we were in the pressed state
45 if (!focusTaken) {
46 // Use a Runnable and post this rather than calling
47 // performClick directly. This lets other visual state
48 // of the view update before click actions start.
49 if (mPerformClick == null) {
50 mPerformClick = new PerformClick();
51 }
52 if (!post(mPerformClick)) {
53 performClick();
54 }
55 }
56 }
57 if (mUnsetPressedState == null) {
58 mUnsetPressedState = new UnsetPressedState();
59 }
60 if (prepressed) {
61 postDelayed(mUnsetPressedState,
62 ViewConfiguration.getPressedStateDuration());
63 } else if (!post(mUnsetPressedState)) {
64 // If the post failed, unpress right now
65 mUnsetPressedState.run();
66 }
67 removeTapCallback();
68 }
69 mIgnoreNextUpEvent = false;
70 break;
71 case MotionEvent.ACTION_DOWN:
72 mHasPerformedLongPress = false;
73 if (performButtonActionOnTouchDown(event)) {
74 break;
75 }
76 // Walk up the hierarchy to determine if we‘re inside a scrolling container.
77 boolean isInScrollingContainer = isInScrollingContainer();
78 // For views inside a scrolling container, delay the pressed feedback for
79 // a short period in case this is a scroll.
80 if (isInScrollingContainer) {
81 mPrivateFlags |= PFLAG_PREPRESSED;
82 if (mPendingCheckForTap == null) {
83 mPendingCheckForTap = new CheckForTap();
84 }
85 mPendingCheckForTap.x = event.getX();
86 mPendingCheckForTap.y = event.getY();
87 postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
88 } else {
89 // Not inside a scrolling container, so show the feedback right away
90 setPressed(true, x, y);
91 checkForLongClick(0);
92 }
93 break;
94 case MotionEvent.ACTION_CANCEL:
95 setPressed(false);
96 removeTapCallback();
97 removeLongPressCallback();
98 mInContextButtonPress = false;
99 mHasPerformedLongPress = false;
100 mIgnoreNextUpEvent = false;
101 break;
102 case MotionEvent.ACTION_MOVE:
103 drawableHotspotChanged(x, y);
104 // Be lenient about moving outside of buttons
105 if (!pointInView(x, y, mTouchSlop)) {
106 // Outside button
107 removeTapCallback();
108 if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
109 // Remove any future long press/tap checks
110 removeLongPressCallback();
111 setPressed(false);
112 }
113 }
114 break;
115 }
116 return true;
117 }
118 return false;
119 }
从源码的21行我们可以看出，该控件可点击就会进入到switch判断中，当我们触发了手指离开的实际，则会进入到MotionEvent.ACTION_UP这个case当中。我们接着往下看，在源码的50行，调用到了mPerformClick()方法，我们继续进入到这个方法的源码看看。
1 public boolean performClick() {
2 final boolean result;
3 final ListenerInfo li = mListenerInfo;
4 if (li != null && li.mOnClickListener != null) {
5 playSoundEffect(SoundEffectConstants.CLICK);
6 li.mOnClickListener.onClick(this);
7 result = true;
8 } else {
9 result = false;
10 }
11 sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
12 return result;
13 }
现在我们可以看到，只要ListenerInfo和mOnClickListener不为null就会调用onClick这个方法，之前说过，只要有监听事件，ListenerInfo就不为null，带mOnClickListener又是在哪里赋值呢？我们再继续看下它的源码。
1 public void setOnClickListener(@Nullable OnClickListener l) {
2 if (!isClickable()) {
3 setClickable(true);
4 }
5 getListenerInfo().mOnClickListener = l;
6 }
看到这里一切就清楚了，当我们调用setOnClickListener方法来给按钮注册一个点击事件时，就会给mOnClickListener赋值。整个分发事件的顺序是onTouch()-->onTouchEvent(event)-->performClick()-->OnClick()。
现在我们可以解决之前的问题。
1、onTouch方法是优先于OnClick，所以是执行了onTouch，再执行onClick。
2、无论是dispatchTouchEvent还是onTouchEvent，如果返回true表示这个事件已经被消费、处理了，不再往下传了。在dispathTouchEvent的源码里可以看到，如果onTouchEvent返回了true，那么它也返回true。如果dispatchTouchEvent在执行onTouch监听的时候，onTouch返回了true，那么它也返回true，这个事件提前被onTouch消费掉了。就不再执行onTouchEvent了，更别说onClick监听了。