事件分发源码分析

View的TouchEvent事件分发源码

View 与 Touch 相关的有两个非常重要的方法

dispatchTouchEvent 事件分发

//默认是false
boolean result = false;
// ListenerInfo li = mListenerInfo;
ListenerInfo li = mListenerInfo;

//如果是enabled而且触摸事件返回为true，则返回true
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//如果result为false则执行onTouchEvent方法,若执行的onTouchEvent为true，则result为true
if (!result && onTouchEvent(event)) {
result = true;
}

点击事件——>在View的onTouchEvent -> case MotionEvent.ACTION_UP: 里面调用了 performClick()——>li.mOnClickListener.onClick(this); 点击事件

onTouchEvent方法（一般都会被我们复写）

测试

首先自定义view

public class TouchView extends View {
public TouchView(Context context) {
super(context);
}

public TouchView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}

public TouchView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e("TAG", "onTouchEvent--->" + event.getAction());
return super.onTouchEvent(event);
}

@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.e("TAG", "dispatchTouchEvent--->" + event.getAction());
return super.dispatchTouchEvent(event);
}
}

使用自定义view

View view = findViewById(R.id.touch_view);
view.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e("TAG","onTouch-->"+event.getAction());
return false;
}
});
view.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e("TAG","onClick");
}
});

分析(0代表down，1代表up，2代表move)

第一种场景:OnTouchListener onTouchEvent dispatchTouchE
fc4e
vent OnClickListener 四个都有的情况下 前提是OnTouchListener 返回false

结果：

dispatchTouchEvent—>0

onTouch–>0

onTouchEvent—>0

dispatchTouchEvent—>2

onTouch–>2

onTouchEvent—>2

dispatchTouchEvent—>1

onTouch–>1

onTouchEvent—>1

onClick

第二种场景:OnTouchListener onTouchEvent dispatchTouchEvent OnClickListener 四个都有的情况下 前提是OnTouchListener 返回true,其他不动

View view = findViewById(R.id.touch_view);
view.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e("TAG","onTouch-->"+event.getAction());
return true;
}
});

此时li.mOnTouchListener.onTouch(this, event)) 方法返回true则不会执行onTouchEvent方法

结果

dispatchTouchEvent—>0

onTouch–>0

dispatchTouchEvent—>2

onTouch–>2

dispatchTouchEvent—>1

onTouch–>1

第三种场景:onTouchEvent dispatchTouchEvent OnClickListener 三个的情况下 设置OnTouchEvent为true

OnTouchEvent默认点击了返回的是true

结果

dispatchTouchEvent—>0

onTouchEvent—>0

dispatchTouchEvent—>2

onTouchEvent—>2

dispatchTouchEvent—>2

dispatchTouchEvent—>1

onTouchEvent—>1

return super.onTouchEvent(event)和return true是有区别的，当设置为true时不会有onClick方法，而默认值会

原因：当设置为true时不会进入view中的onTouchEvent方法

第四种场景:OnTouchListener onTouchEvent dispatchTouchEvent OnClickListener 四个的情况下 设置dispatchTouchEvent 为true，其他的返回原样

@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.e("TAG", "dispatchTouchEvent--->" + event.getAction());
return true;
}

结果

dispatchTouchEvent—>0

dispatchTouchEvent—>2

dispatchTouchEvent—>1

view的dispatch的方法不会被执行

ViewGroup 的事件分发 源码分析

首先准备工作

将原本activity_main布局中的LinearLayout换成自定义View的TouchViewGroup

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

public TouchViewGroup(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}

public TouchViewGroup(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}

//事件分发
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.e("TAG", "ViewGroup dispatchTouchEvent--->" + event.getAction());//这是自己的处理事件
return super.dispatchTouchEvent(event);
}

//事件拦截
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.e("TAG", "ViewGroup onInterceptTouchEvent--->" + ev.getAction());//这是自己的处理事件
return super.onInterceptTouchEvent(ev);
}

//事件触摸
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e("TAG", "ViewGroup onTouchEvent--->" + event.getAction());//这是自己的处理事件
return super.onTouchEvent(event);
}
}

并修改其中的view打印事件

View view = findViewById(R.id.touch_view);
view.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
Log.e("TAG", "View onTouch-->" + event.getAction());
return false;
}
});
view.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.e("TAG", "onClick");
}
});

public class TouchView extends View {
public TouchView(Context context) {
super(context);
}

public TouchView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}

public TouchView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e("TAG", "View onTouchEvent--->" + event.getAction());//这是自己的处理事件
return super.onTouchEvent(event);//默认返回true
//而点击事件是系统的UP中的事件,所以你返回true的时候并没有进入系统中的
//return true;
}

@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.e("TAG", "View dispatchTouchEvent--->" + event.getAction());
return super.dispatchTouchEvent(event);
}
}

dispatchTouchEvent() 源码看看

boolean handled = false;

// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// 清除TouchTargets 只要知道 mFirstTouchTarget = null
cancelAndClearTouchTargets(ev);
resetTouchState();
}

final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {//disallowIntercept==false
intercepted = onInterceptTouchEvent(ev);//默认返回false
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;
}

TouchTarget newTouchTarget = null;
if (!canceled && !intercepted) {
if (newTouchTarget == null && childrenCount != 0) {//ACTION_DOWN
for (int i = childrenCount - 1; i >= 0; i--) {// 反序的for循环  获取子View child
newTouchTarget = getTouchTarget(child);
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// 如果子 View 返回true 就会进来 主要给 mFirstTouchTarget = target; 赋值
addTouchTarget(child, idBitsToAssign);
}
}
}

}

/**
* Clears all touch targets. * mFirstTouchTarget = null; 这句话核心清除 mFirstTouchTarget
*/
private void clearTouchTargets() {
TouchTarget target = mFirstTouchTarget;
if (target != null) {
do {
TouchTarget next = target.next;
target.recycle();
target = next;
} while (target != null);
mFirstTouchTarget = null;
}
}

private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) {
final boolean handled;
// Canceling motions is a special case.  We don't need to perform any transformations
// or filtering.  The important part is the action, not the contents.
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
// child == null 会调用 自己的 super View.dispatchTouchEvent(event)
handled = super.dispatchTouchEvent(event);
} else {
// child == null 会调用 自己的 super View.dispatchTouchEvent(event)
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
}

onInterceptTouchEvent() 源码看看

onTouchEvent() 源码看看

场景分析

第一种常见，View和ViewGroup的TouchEvent全部设置为默认

结果:

ViewGroup dispatchTouchEvent—>0

ViewGroup onInterceptTouchEvent—>0

View dispatchTouchEvent—>0

View onTouch–>0

View onTouchEvent—>0

ViewGroup dispatchTouchEvent—>2

ViewGroup onInterceptTouchEvent—>2

View dispatchTouchEvent—>2

View onTouch–>2

View onTouchEvent—>2

ViewGroup dispatchTouchEvent—>1

ViewGroup onInterceptTouchEvent—>1

View dispatchTouchEvent—>1

View onTouch–>1

View onTouchEvent—>1

即正常情况下:

第一次DOWN

ViewGroup.dispatchTouchEvent ->ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent ->View.onTouch -> View.onTouchEvent

第二次MOVE

ViewGroup.dispatchTouchEvent -> ViewGroup onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch ->View.onTouchEvent

第三次UP

ViewGroup.dispatchTouchEvent -> ViewGroup onInterceptTouchEvent    ->  View.onTouch -> View.onTouchEvent -> View.onclick

第二种情况：onClick 没有 理解为没有消费事件,即没有进入onClick方法不返回true

ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View onTouchEvent -> ViewGroup.onTouchEvent

第三种情况:在 View 的 onTouchEvent() 方法里面返回true 的情况下

第一次DOWN ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent

第二次MOVE ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent

第三次UP ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.onTouch -> View.onTouchEvent

第四种情况:在 ViewGroup 的 onInterceptTouchEvent() 方法里面返回 true 的情况下

ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> ViewGroup.onTouchEvent

总结

1.如果说子 View 没有一个地方返回 true ,只会进来一次只会响应 DOWN 事件,代表不需要消费该事件,如果你想响应 MOVE,UP 必须找个地方ture

2.对于ViewGroup来讲，如果你想拦截子 View 的 Touch 事件，可以覆写 onInterceptTouchEvent 返回 true 即可 , 如果说 onInterceptTouchEvent 返回的是 true 会执行该 ViewGroup 的 onTouchEvent 方法 , 如果子 View 没有消费 touch 事件也会调用该 ViewGroup 的 onTouchEvent 方法