从源码角度带你分析 Android View 事件分发 dispatchTouchEvent，onTouch，onTouchEvent，onClick逻辑顺序过程
我们先从一个例子看起，先重写一个MyButton 继承Button，代码如下：
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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);
}
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布局文件如下：
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<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：
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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：
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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：
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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;
}
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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！！！）
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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;
}
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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：
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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;
}
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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。