我们先从一个例子看起，先重写一个MyButton 继承Button，代码如下：
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 public class MyBtn extends Button { public MyButton(Context context) { super (context); } public MyBtn(Context context, AttributeSet attrs) { super (context, attrs); } public MyBtn(Context context, AttributeSet attrs, int defStyleAttr) { super (context, attrs, defStyleAttr); } @Override public boolean dispatchTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: MyLog.e( "dispatchTouchEvent====MyButton=====ACTION_DOWN" ); break ; case MotionEvent.ACTION_MOVE: MyLog.e( "dispatchTouchEvent====MyButton=====ACTION_MOVE" ); break ; case MotionEvent.ACTION_UP: MyLog.e( "dispatchTouchEvent====MyButton=====ACTION_UP" ); break ; } return super .dispatchTouchEvent(event); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: MyLog.e( "onTouchEvent====MyButton=====ACTION_DOWN" ); break ; case MotionEvent.ACTION_MOVE: MyLog.e( "onTouchEvent====MyButton=====ACTION_MOVE" ); break ; case MotionEvent.ACTION_UP: MyLog.e( "onTouchEvent====MyButton=====ACTION_UP" ); break ; } return super .onTouchEvent(event); }
布局文件如下：
? 1 2 3 4 5 <relativelayout android:layout_height= "match_parent" android:layout_width= "match_parent" android:paddingbottom= "@dimen/activity_vertical_margin" android:paddingleft= "@dimen/activity_horizontal_margin" android:paddingright= "@dimen/activity_horizontal_margin" android:paddingtop= "@dimen/activity_vertical_margin" tools:context= ".MainActivity" xmlns:android= "http://schemas.android.com/apk/res/android" xmlns:tools= "http://schemas.android.com/tools" > <com.xjp.testtouchevent.mybutton android:id= "@+id/myButton" android:layout_height= "wrap_content" android:layout_width= "wrap_content" android:text= "测试" > </com.xjp.testtouchevent.mybutton></relativelayout> 测试Activity如下：
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 public class MainActivity extends ActionBarActivity { private Button myButton; @Override protected void onCreate(Bundle savedInstanceState) { super .onCreate(savedInstanceState); setContentView(R.layout.activity_main); myButton = (Button) findViewById(R.id.myButton); myButton.setOnTouchListener( new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: MyLog.e( "onTouch====MyButton=====ACTION_DOWN" ); break ; case MotionEvent.ACTION_MOVE: MyLog.e( "onTouch====MyButton=====ACTION_MOVE" ); break ; case MotionEvent.ACTION_UP: MyLog.e( "onTouch====MyButton=====ACTION_UP" ); break ; } return false ; } }); myButton.setOnClickListener( new View.OnClickListener() { @Override public void onClick(View v) { MyLog.e( "onClick====MyButton=====onClick" ); } }); } } 点击测试按钮，打印结果如下：
我们从打印结果可以直观看到，点击Button按钮事件分发过程如下 dispatchTouchEvent---->onTouch---->onTouchEvent----->onClick。并且如果仔细的你会发现，都是在ACTION_UP事件之后才触发onClick点击事件，为什么会是这样？？现在我们不得而知。我们仅仅是从打印结果推测事件分发的结论，现在我们从源码分析下这个事件分发流程为什么是这样子。
事件分发都是从dispatchTouchEvent方法开始的，那么我们这里是重写了dispatchTouchEvent方法，并且最后也调用了父类的super.dispatchTouchEvent(event)方法。那么我们看看父类中的方法到底做了什么？？点击进入父类的dispatchTouchEvent方法，发现此方法在View类中找到，其实也不奇怪，所有控件的父类都是View。这里我贴出最新源码如下：
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 public boolean dispatchTouchEvent(MotionEvent event) { 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)) { 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; }
忽略其他无关代码，我们直接看17--25行。第17行的if判断关键在于li.mOnTouchListener.onTouch(this, event) 的返回值，这个接口回调就是我们外面写的myButton.setOnTouchListener事件（Button 的onTouch事件），在MainActivity代码里，我们setOnTouchListener返回的值是false，所以在源码中我们可以看到 17行的条件不成立，那么条件不成立，result=false；因此，源码的第23行if 判断第一个条件成立，继续执行第二个条件，也就是onTouchEvent。我们跳到这个方法里看看里面干啥了？看如下代码：
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 public boolean onTouchEvent(MotionEvent event) { if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) { switch (event.getAction()) { 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) { // 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(); } break ; return true ; } return false ; } 我们看看这里边都做了些什么，忽略其他，我们直接看37行的 performClick(); 方法，跳进去继续看，（注意：这里的performClick方法是在ACTION_UP手势里边执行的哦！！！）
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 public boolean performClick() { final boolean result; final ListenerInfo li = mListenerInfo; if (li != null && li.mOnClickListener != null ) { playSoundEffect(SoundEffectConstants.CLICK); li.mOnClickListener.onClick( this ); result = true ; } else { result = false ; } sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED); return result; } 看见没？？第6行 li.mOnClickListener.onClick(this); 这个接口回调就是我们Button的 onClick事件。到此为止，我们从源码分析了Button事件分发过程 结论：dispatchTouchEvent---->onTouch---->onTouchEvent----->onClick。并且如果仔细的你会发现，是在所有ACTION_UP事件之后才触发onClick点击事件。
现在我们来看看其他情况：当onTouch返回为true，打印结果如下：
惊奇的发现，竟然没有执行onClick事件是吧？？？？如果你仔细阅读上面的文章，估计你知道为什么了吧？还是跟大家一起分析一下吧：源码如下：
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 public boolean dispatchTouchEvent(MotionEvent event) { 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)) { 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; } 从第17行可以看出，条件成立，result=true；那么第23行if条件根本不会执行第二个判断，那么就不会执行onTouchEvent方法，也就不会调用 onClick的接口，因此Button 不会执行setOnClickListener中的onClick事件。
给个简单的流程图如下
因此，事件分发之间的关系是：dispatchTouchEvent方法中线执行 onTouch接口回调，然后根据onTouch方法的返回值判断是否执行onTouchEvent方法，onTouchEvent方法中执行了onClick接口回调。
