点击事件的传递
public boolean dispatchTouchEvent(MotionEvent event)：如果事件能够传递给当前view，那么此方法肯定会调用。该方法返回的结果受当前的View的onTouchEvent和下级的dispatchTouchEvent 的影响，表示是否消耗当前事件
首先从最上层看Acticity中的dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
可以看到这里主要通过getWindow的superDispatchTouchEvent方法来判断是否拦截事件，我们知道Activity中的Window是PhoneWindow，所以我们看下PhoneWindow怎么来处理这个事件,
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
phoneWindow中又是通过decorView来处理这个事件的，
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
因为DecorView又是继承ViewGroup的，所以最终还是调用了ViewGroup 的dispatchTouchEvent方法，ViewGroup中的处理分为三个步骤：
步骤 1：判断当前 ViewGroup 是否需要拦截此 touch 事件，如果拦截则此次 touch 事件不再会传递给子 View（或者以 CANCEL 的方式通知子 View）。
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;
}
如果事件为 DOWN 事件，则调用 onInterceptTouchEvent 进行拦截判断；
或者 mFirstTouchTarget 不为 null(当有子元素成功处理时，mFirstTouchTarget 会被赋值并指向子元素)，代表已经有子 View 捕获了这个事件，子 View 的 dispatchTouchEvent 返回 true 就是代表捕获 touch 事件。
此处的FLAG_DISALLOW_INTERCEPT标志意味着子View使用了requestDisallowInterceptTouchEvent方法。
步骤 2：当ViewGroup不拦截事件时，接下来会遍历所有的子View，当坐标落在当前View的区域内且当前View未在播放动画，那么事件就会传递给View处理：
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
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;
}
这里的dispatchTransformedTouchEvent其实也是调用了子View的dispatchTouchEvent方法
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;
}
如果这个方法返回true，那么mFirstTouchTarget会被赋值，证明事件被处理：
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
步骤 3：根据 mFirstTouchTarget 重新分发事件。如果子元素都没有处理事件，那么此时ViewGroup就会自己处理这个事件，
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
这里的super.dispatchTouchEvent(event)其实就是调用的View的dispatchTouchEvent方法：
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//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;
}
}
首先看下View是否被设置OnTouchListener，可以看到如果设置了OnTouchListener且返回值为true，那么onTouchEvent方法就不会被调用，所以OnTouchListener优先级更高，接着我们看下onTouchEvent：
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
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;
}
只要CLICKABLE和LONG_CLICKABLE有一个为true，那么就会消耗这个事件
case MotionEvent.ACTION_UP:
......
performClick();
可以看到在UP事件后会调用performClick方法，所以只要设置了当前View的点击事件，此处就会触发。
