注： 分析的是Android28的源码
一 Activity分发到顶层View
Activity#dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == 0) {
this.onUserInteraction();
}
//事件交给Activity附属的window来处理，
//如果返回true,事件就结束了
//如果返回false,表示没人处理，那么Activity自己来处理，即this.onTouchEvent
return this.getWindow().superDispatchTouchEvent(ev) ? true : this.onTouchEvent(ev);
}
window是抽象类，superDispatchTouchEvent是抽象方法
Window#superDispatchTouchEvent
public abstract boolean superDispatchTouchEvent(MotionEvent var1);
我们找到window的唯一实现类PhoneWindow
PhoneWindow#superDispatchTouchEvent
public boolean superDispatchTouchEvent(MotionEvent event) {
return this.mDecor.superDispatchTouchEvent(event);
}
mDecor是DecorView,
DecorView#superDispatchTouchEvent
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
DecorView是setContentView（）中设置的布局的父布局。DecorView是FrameLayout的子类，但是FrameLayout并没有实现dispatchTouchEvent,于是实际调用的是ViewGroup的dispatchTouchEvent。
至此，事件已经从Activity传到window,再传到了DecorView
二 顶层View向下分发
ViewGroup#dispatchTouchEvent核心代码
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//2. 接收down事件时清空mFirstTouchTarget
if (actionMasked == MotionEvent.ACTION_DOWN) {
cancelAndClearTouchTargets(ev);
resetTouchState();
}
//1. ViewGroup是否拦击
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
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;
}
//3. ViewGroup不拦截，向下分发
if (!canceled && !intercepted) {
for (int i = childrenCount - 1; i >= 0; i--) {
//3.1 子控件是否能接收点击事件
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//3.2 调用子View的dispatchTouchEvent()
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();
//3.3 若子控件的dispatchTouchEvent()返回true
//给mFirstTouchTarget 赋值
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}
}
//4. 若mFirstTouchTarget == null(无子控件处理事件)，则自己来处理
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
...
}
}
2.1 ViewGroup是否拦截
2.1.1 ViewGroup有两种情况判断是否拦截当前事件
actionMasked == MotionEvent.ACTION_DOWN
或者
mFirstTouchTarget != null
2.1.2 从后面代码会了解到，当ViewGroup不拦截事件，并传递给子元素处理事件后，mFirstTouchTarget！=null,也就是说，一旦ViewGroup拦截了事件，那么ACTION_DOWN后续的事件（MOVE UP）都不会在判断是否需要拦截，也就不会执行onInterceptTouchEvent()
2.1.3 FLAG_DISALLOW_INTERCEPT标志位
这个标志位是在ViewGroup的子View中通过
//intercept： 若不希望父控件拦截事件，传入true
getParent().requestDisallowInterceptTouchEvent(boolean intercept);
设置的。但是这个设置并不能拦截父控件的down事件，因为ViewGroup接收到Down会重置这个状态，使标志位设置失效，具体请看2.2
2.2 接收Down事件重置状态
在接收到down事件时，会把mFirstTouchTarget 设置为null,并清空FLAG_DISALLOW_INTERCEPT标志位
2.3 ViewGroup不拦截事件，会遍历所有子控件，将事件分发给子控件
2.3.1 子控件是否能接收点击事件，若不能，直接continue。
下面的两个条件要同时满足
//一： 1. 可见 或者 2. 有动画
private static boolean canViewReceivePointerEvents(@NonNull View child) {
return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null;
}
//二： 点击的坐标落在控件的区域内
protected boolean isTransformedTouchPointInView(float x, float y, View child,PointF outLocalPoint) {
final float[] point = getTempPoint();
point[0] = x;
point[1] = y;
transformPointToViewLocal(point, child);
final boolean isInView = child.pointInView(point[0], point[1]);
if (isInView && outLocalPoint != null) {
outLocalPoint.set(point[0], point[1]);
}
return isInView;
}
2.3.2 调用子控件的dispatchTouchEvent
ViewGroup#dispatchTransformedTouchEvent
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits) {
boolean handled;
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
...
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
3.3 子控件的dispatchTouchEvent返回true,那么会给mFirstTouchTarget赋值并跳出ViewGroup对子控件的for循环遍历 。
ViewGroup#addTouchTarget()
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
3.4 若无子控件处理事件，则自己来处理
注意 传入的第三个参数child是null
ViewGroup#dispatchTransformedTouchEvent
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits) {
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
}
super.dispatchTouchEvent()即交给View来处理
三 View对事件的处理
View#dispatchTouchEvent()核心代码
public boolean dispatchTouchEvent(MotionEvent event) {
...
boolean result = false;
...
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
//1. onTouchLisenter
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//2. onTouchEvent() //3. onTouchEvent分析
if (!result && onTouchEvent(event)) {
result = true;
}
}
...
return result;
}
3.1. 最先调用的是OnTouchListener的onTouch()
- 若onTouch()返回true,则result为true
- 若onTouch()返回false,则result为false.
- result会影响onTouchEvent()的执行与否
3.2. 是否执行onTouchEvent
若result为true, if(!result && onTouchEvent(event))的！result就是false了，由于&&短路原则，就不会执行onTouchEvent(event)了。
3.3. onTouchEvent分析
View#onTouchEvent()
public boolean onTouchEvent(MotionEvent event) {
//1. 状态不可用的View也会消费事件，只是不响应事件
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return clickable;
}
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
...
// 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)) {
//2. 执行点击事件
performClickInternal();
}
}
}
...
break;
}
//3. 只要是clickable 就会return true
return true;
}
3.3.1 状态不可用的View也会消费事件，只是不响应事件
3.3.2 执行点击事件
private boolean performClickInternal() {
notifyAutofillManagerOnClick();
return performClick();
}
public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
//5. onTouchEvent最终会调用onClick
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
...
return result;
}
3.3.3 onTouchEvent消费事件
View的onTouchEvent默认都会消费事件（返回true），除非他是不可点击的（clickable和longclickable都是false）.
longClickable默认是false;
clickable不同控件的情况不一样，如Button的clickable就是true。
水平有限，有错误欢迎指正！！
网友评论