Android事件分发机制——View（一）
在分析分发机制之前，我们来了解一些预备知识。
- onTouch是优先于onClick执行，事件传递的顺序是先经过onTouch，再传递到onClick；
- MotionEvent对象的四种状态：
MotionEvent.ACTION_DOWN：手指按下屏幕的瞬间。
MotionEvent.ACTION_MOVE：手指在屏幕上移动
MotionEvent.ACTION_UP：手指离开屏幕瞬间
MotionEvent.ACTION_CANCEL：取消手势
- Android事件响应机制是“由外到内”分发、“由内到外”处理的形式实现的；
- Android中的事件onClick、onLongClick、onScroll等，都是由多个Touch事件（一个ACTION_DOWN,多个ACTION_MOVE,一个ACTION_UP）组成；
- Android事件分发机制主要由“事件分发”—>“事件拦截”—>“事件响应”这三步来进行逻辑控制的；
- ViewGroup中的分发机制三个方法：
public boolean dispatchTouchEvent(MotionEvent ev)；
public boolean onInterceptTouchEvent(MotionEvent ev);
public boolean onTouchEvent(MotionEvent ev);
- View中的分发机制两个方法：
public boolean dispatchTouchEvent(MotionEvent ev)；
public boolean onTouchEvent(MotionEvent ev);
案例
public class MyButton extends Button {
private static String TAG = MyButton.class.getSimpleName();
public MyButton(Context context) {
super(context);
}
public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onTouchEvent ACTION_UP");
break;
default:
break;
}
return super.onTouchEvent(event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "dispatchTouchEvent ACTION_UP");
break;
default:
break;
}
return super.dispatchTouchEvent(event);
}
}
<LinearLayout 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"
tools:context=".MainActivity">
<com.example.dispatchevent.MyButton
android:id="@+id/my_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="click me"/>
LinearLayout>
public class MainActivity extends AppCompatActivity {
private static String TAG = "MyButton";
private Button mButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mButton = findViewById(R.id.my_button);
mButton.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
int action = motionEvent.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onTouch ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onTouch ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onTouch ACTION_UP");
break;
default:
break;
}
return false;
}
});
mButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e(TAG, "onclick");
}
});
mButton.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
Log.e(TAG, "longclick");
return false;
}
});
}
}
好了，跟View事件相关一般就三个地方，一个onTouchEvent，一个dispatchTouchEvent，一个setOnTouchListener；
我们来看一下日志输出：
01-07 22:20:38.992 24590-24590/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_DOWN
01-07 22:20:38.992 24590-24590/com.example.dispatchevent E/MyButton: onTouch ACTION_DOWN
01-07 22:20:38.992 24590-24590/com.example.dispatchevent E/MyButton: onTouchEvent ACTION_DOWN
01-07 22:20:39.016 24590-24590/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_MOVE
01-07 22:20:39.016 24590-24590/com.example.dispatchevent E/MyButton: onTouch ACTION_MOVE
01-07 22:20:39.016 24590-24590/com.example.dispatchevent E/MyButton: onTouchEvent ACTION_MOVE
01-07 22:20:39.019 24590-24590/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_UP
01-07 22:20:39.020 24590-24590/com.example.dispatchevent E/MyButton: onTouch ACTION_UP
01-07 22:20:39.020 24590-24590/com.example.dispatchevent E/MyButton: onTouchEvent ACTION_UP
01-07 22:20:39.029 24590-24590/com.example.dispatchevent E/MyButton: onclick
好了，可以看到，不管是DOWN，MOVE，UP都会按照下面的顺序执行：
- dispatchTouchEvent
- setOnTouchListener的onTouch
- onTouchEvent
源码分析
首先你需要知道一点，只要你触摸到了任何一个控件，就一定会调用该控件的dispatchTouchEvent方法，由于Button中没有会一直向上寻找，最终发现View.dispatchTouchEvent。
View.dispatchTouchEvent
/**
* 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 (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
mOnTouchListener.onTouch(this, event)) {
return true;
}
return onTouchEvent(event);
}
/**
* Register a callback to be invoked when a touch event is sent to this view.
* @param l the touch listener to attach to this view
*/
public void setOnTouchListener(OnTouchListener l) {
mOnTouchListener = l;
}
首先判断mOnTouchListener不为null，并且view是enable的状态，然后 mOnTouchListener.onTouch(this, event)返回true，这三个条件如果都满足，直接return true，也就是下面的onTouchEvent(event)不会被执行了；
我们在看一个简单的示例：
mButton.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
int action = motionEvent.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onTouch ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onTouch ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onTouch ACTION_UP");
break;
default:
break;
}
return true;
//return false;
}
});
01-07 04:23:35.132 14251-14251/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_DOWN
01-07 04:23:35.134 14251-14251/com.example.dispatchevent E/MyButton: onTouch ACTION_DOWN
01-07 04:23:35.154 14251-14251/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_MOVE
01-07 04:23:35.156 14251-14251/com.example.dispatchevent E/MyButton: onTouch ACTION_MOVE
01-07 04:23:35.163 14251-14251/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_UP
01-07 04:23:35.164 14251-14251/com.example.dispatchevent E/MyButton: onTouch ACTION_UP
从这个示例中我们看到，如果onTouch中返回true，从而使onTouchEvent就不会执行并且onClick也没有执行，从而得出结论onTouch要优先于onClick之前被执行，并且onClick是在onTouchEvent中被执行的。
View.onTouchEvent
/**
* Implement this method to handle touch screen motion events.
*
* @param event The motion event.
* @return True if the event was handled, false otherwise.
*/
public boolean onTouchEvent(MotionEvent event) {
final int viewFlags = mViewFlags;
if ((viewFlags & ENABLED_MASK) == DISABLED) {
// 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));
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
//（1）此处肯定返回true
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
switch (event.getAction()) {
//（4）MotionEvent.ACTION_UP操作
case MotionEvent.ACTION_UP:
boolean prepressed = (mPrivateFlags & PREPRESSED) != 0;
if ((mPrivateFlags & 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 (!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) {
mPrivateFlags |= PRESSED;
refreshDrawableState();
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
break;
//（2）MotionEvent.ACTION_DOWN操作
case MotionEvent.ACTION_DOWN:
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPrivateFlags |= PREPRESSED;
mHasPerformedLongPress = false;
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
break;
case MotionEvent.ACTION_CANCEL:
mPrivateFlags &= ~PRESSED;
refreshDrawableState();
removeTapCallback();
break;
//（3）MotionEvent.ACTION_MOVE状态判断
case MotionEvent.ACTION_MOVE:
final int x = (int) event.getX();
final int y = (int) event.getY();
// Be lenient about moving outside of buttons
int slop = mTouchSlop;
if ((x < 0 - slop) || (x >= getWidth() + slop) ||
(y < 0 - slop) || (y >= getHeight() + slop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback();
// Need to switch from pressed to not pressed
mPrivateFlags &= ~PRESSED;
refreshDrawableState();
}
}
break;
}
return true;
}
return false;
}
分析：
（1）
首先我们需要注意的是在23行，onTouchEvent肯定是返回true的，接下来就是 switch (event.getAction())了，判断事件类型，DOWN,MOVE,UP等；
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
//...
return true;
}
（2）MotionEvent.ACTION_DOWN
case MotionEvent.ACTION_DOWN:
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPrivateFlags |= PREPRESSED;
mHasPerformedLongPress = false;
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
break;
- 先将mPrivateFlags设置一个PREPRESSED的标识
- 并且设置mHasPerformedLongPress=false，表示长按事件还未触发
- 最后发送一个延迟为ViewConfiguration.getTapTimeout()的延迟消息，到达延时时间后会执行CheckForTap()里面的run方法
private final class CheckForTap implements Runnable {
public void run() {
//取消mPrivateFlags的PREPRESSED，然后设置PRESSED标识
mPrivateFlags &= ~PREPRESSED;
mPrivateFlags |= PRESSED;
//刷新背景
refreshDrawableState();
//如果View支持长按事件，则再发一个延时消息，检测长按
if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
postCheckForLongClick(ViewConfiguration.getTapTimeout());
}
}
}
private void postCheckForLongClick(int delayOffset) {
mHasPerformedLongPress = false;
if (mPendingCheckForLongPress == null) {
mPendingCheckForLongPress = new CheckForLongPress();
}
mPendingCheckForLongPress.rememberWindowAttachCount();
//发送延迟消息，执行CheckForLongPress中run方法，500ms之后触发performLongClick()，之前都算是performOnClick()
postDelayed(mPendingCheckForLongPress,
ViewConfiguration.getLongPressTimeout() - delayOffset);
}
class CheckForLongPress implements Runnable {
private int mOriginalWindowAttachCount;
public void run() {
if (isPressed() && (mParent != null)
&& mOriginalWindowAttachCount == mWindowAttachCount) {
//调用长按事件，当返回为true时，将mHasPerformedLongPress设置为true，从而使Move_Up中的performOnClick无法执行
if (performLongClick()) {
mHasPerformedLongPress = true;
}
}
}
- 如果此时设置了长按的回调，则执行长按时的回调，且如果长按的回调返回true，才把mHasPerformedLongPress置为ture；
- 否则，如果没有设置长按回调或者长按回调返回的是false，则mHasPerformedLongPress依然是false；
（3）MotionEvent.ACTION_MOVE
简单来说就是先拿到当前触摸的x,y坐标，然后判断触摸是否移出当前View，如果移出了将清除之前的标识以及removeCallbacks等操作；
（4）MotionEvent.ACTION_UP
//之前如果没有执行performLongClick或者返回值为false，mHasPerformedLongPress将为false；
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();
}
}
}
public boolean performClick() {
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
if (mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
mOnClickListener.onClick(this);
return true;
}
return false;
}
之前也说了，如果没有设置长按回调或者长按回调返回的是false，则mHasPerformedLongPress依然是false，此时将满足条件，从而会执行performClick()。
另外最后还会执行UnsetPressedState.run()；
private final class UnsetPressedState implements Runnable {
@Override
public void run() {
setPressed(false);
}
}
public void setPressed(boolean pressed) {
final boolean needsRefresh = pressed != ((mPrivateFlags & PFLAG_PRESSED) == PFLAG_PRESSED);
if (pressed) {
mPrivateFlags |= PFLAG_PRESSED;
} else {
mPrivateFlags &= ~PFLAG_PRESSED;
}
if (needsRefresh) {
refreshDrawableState();
}
dispatchSetPressed(pressed);
}
//可以重新此方法
protected void dispatchSetPressed(boolean pressed) {
}
总结
（1）View的事件转发流程
View.dispatchTouchEvent->View.setOnTouchListener->View.onTouchEvent
在dispatchTouchEvent中会进行OnTouchListener的判断，如果OnTouchListener不为null且返回true，则表示事件被消费，onTouchEvent不会被执行，否则执行onTouchEvent。
（2）Down时
- 首先设置标志为PREPRESSED，设置mHasPerformedLongPress=false，然后发出一个115ms后的mPendingCheckForTap；
- 如果115ms内没有触发UP，则将标志置为PRESSED，清除PREPRESSED标志，同时发出一个延时为500-115ms的，检测长按任务消息；
- 如果500ms内（从DOWN触发开始算），则会触发LongClickListener；
- 超过500ms，此时如果LongClickListener不为null，则会执行回调，同时如果LongClickListener.onClick返回true，才把mHasPerformedLongPress设置为true，否则mHasPerformedLongPress依然为false；
（3）Move时
主要就是检测用户是否划出控件，如果划出将清除标识以及removeCallback等；
（4）Up时
- 如果115ms内，触发UP，此时标志为PREPRESSED，则执行UnsetPressedState，setPressed(false)，会把setPress转发下去，可以在View中复写dispatchSetPressed方法接收；
- 如果是115ms-500ms间，即长按还未发生，则首先移除长按检测，执行onClick回调；
- 如果超过500ms以后，设置了onLongClickListener，且onLongClickListener.onClick返回true，则点击事件OnClick事件无法触发，如果没有设置onLongClickListener或者onLongClickListener.onClick返回false，则点击事件OnClick事件依然可以触发；
- 最后执行mUnsetPressedState.run()，将setPressed传递下去；
最后一个问题
问：setOnLongClickListener和setOnClickListener是否只能执行一个？
答：不是的，只要setOnLongClickListener中的onLongClick返回false，则两个都会执行；返回true则会屏蔽setOnClickListener。