View的事件分发
1.View的事件分发
View的事件分发主要涉及到三个方:dispatchTouchEvent、onTouchEvent、onInterceptTouchEvent
- dispatchTouchEvent(MotionEvent ev)
用来进行事件分发。如果事件能够传递给当前View,那么此方法一定会被调用，返回结果受 当前View的onTouchEvent和下级View的dispatchTouchEvent方法影响，表示是否消费事件
- onTouchEvent(MotionEvent ev)
在dispatchTouchEvent方法中调用，用来处理点击事件，返回结果表示是否消费当前事件，如果不消费，则在同一个事件序列中，当前View无法在接收此事件。
- onInterceptTouchEvent(MotionoEvent ev)
用来判断是否拦截某个事件，如果当前View拦截某个事件，那么在同一个事件序列当中，此方法不会被再次调用，返回结果表示是否拦截当前事件。
三者关系
public boolean dispatchTouchEvent(MotionoEvent ev){
boolean consume=false;
if( onInterceptTouchEvent(ev)){
consume=onTouchEvent(ev);
}else{
consume=child. dispatchTouchEvent(ev)
}
return consume;
}
传递规则：对于ViewGroup来说,点击事件后 ->dispatchTouchEvent()-> onInterceptTouchEvent()->child.dispatchTouchEvent,如此反复直到事件被最终处，如果onInterceptTouchEvent返回ture，则dispatchTouchEvent()-> onInterceptTouchEvent()->onTouchEvent();
对于一个View需要处理事件，如果设置了OnTouchListener,那么onTouchListener中的onTouch方法会被调用，如果返回false，则onTouchEvent会调用，如果返回ture 则不会调用,
首先进到dispatchTouchEvent方法
public boolean dispatchTouchEvent(MotionEvent event) {
...
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
// 当设置了OnTouchListener.onTouch为true 是这个方法能进去 result=true
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
// 上面result =ture 所用这个onTouchEvent方法就调用不到了,所以这不会走这个方法，
//onTouchEvent 点击事件是这里面调用的往后看，
if (!result && onTouchEvent(event)) {
result = true;
}
}
return result;
}
当OnTouchListener.onTouch返回true时，会走到onTouchEvent方法
public boolean onTouchEvent(MotionEvent event) {
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
if (!focusTaken) {
// 点击事件
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClickInternal();
}
}
}
return true;
}
return false;
}
private boolean performClickInternal() {
// Must notify autofill manager before performing the click actions to avoid scenarios where
// the app has a click listener that changes the state of views the autofill service might
// be interested on.
notifyAutofillManagerOnClick();
return performClick();
}
//返回result
public boolean performClick() {
// We still need to call this method to handle the cases where performClick() was called
// externally, instead of through performClickInternal()
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);//点击事件
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
}
得出一个结论:View的OnTouchListener优先级高于onTouchEent高于OnClickListener，
3.ViewGroup事件分发
ViewGroup比View相对而言复杂些
传递过程遵循如下顺序:Activity ->Window ->View 但事件没有消费最终也是传递给Activity 处理。
事件传递过程是由外到内，及事件总是先传递给父元素，然后在分发子view，通过
requestDisallowInterceptTouchEvent方法可以在子元素中干预父元素的事件分发过程(ViewPager 源码中就有这句话)，但是ACTION_DOWN事件除外
2.源码分析
先看Activity 是怎么传递给window然后在传给view
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
// 当没有消费事件，则调用自己的onTouchEvent
return onTouchEvent(ev);
}
getWindow().superDispatchTouchEvent(ev) 是调去了window的dispatchTouchEvent, getWindow返回一个Window 抽象类，具体实现是PhoneWindow.class
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
// mDecor 是DecorView，
return mDecor.superDispatchTouchEvent(event);
}
//DecorView 每个布局的跟布局，其实setContentView设置的View 是它的一个子View
@Override
public final @NonNull View getDecorView() {
if (mDecor == null || mForceDecorInstall) {
installDecor();
}
return mDecor;
}
由于DecorView继承FrameLayout且是父View，而FrameLayout 是基础ViewGroup，
接下来直接看ViewGroup,调用则是ViewGroup.dispatchTouchEven()方法，
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final boolean intercepted;
// mFirstTouchTarg当事件由ViewGroup 子元素成功处理时赋值，
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//FLAG_DISALLOW_INTERCEPT 是子View调用了requestDisallowInterceptTouchEvent来设置的
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
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;
}
}
上文又说到为什么ACTION_DOWN事件除外？
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
cancelAndClearTouchTargets(ev);
resetTouchState();//
}
//重置了所以值
private void resetTouchState() {
clearTouchTargets();
resetCancelNextUpFlag(this);
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
mNestedScrollAxes = SCROLL_AXIS_NONE;
}
当ViewGroup 不拦截事件，事件向下分发
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
resetCancelNextUpFlag(child);
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
通过遍历ViewGroup的所有方法，然后调用dispatchTransformedTouchEvent 看这个方法 实际上是调用了子View.dispathTouchEvent()
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
return handled;
}
如果子元素的dispathTouchEvent返回true,这时，那么mFirstTouchTarget就会被赋值跳出循环
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
mFirstTouchTarget是一个单链表结构，如果mFirstTouchTarget=null 那么ViewGroup就默认拦截接下来同一序列中所用的点击事件
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
如果dispathTouchEvent返回false,那么ViewGroup就会把事件分发给下一个子元素(如果还有下一个子元素)
