要从源码理解整个事件传递过程，必须先从事件传递的返回值认清整个事件的消费过程，对整个事件有大致的了解，为何事件被消费，为何由子类消费
需要注意的几个点
主要这三个方法
dispatchTouchEvent() —— true消费，false不消费（即为分发）；false表示事件停止往下面的视图层级进行传递，同时开始往上面的视图层级的onTouchEvent传递，也称为回溯。
oninterceptTouchEvent() —— true消费，false不消费（即为不拦截）
onTouchEvent() —— true消费，false不消费（）
而事件分发一般会经过视图的三个层级：Activity、ViewGroup、View。下表会对视图不同的三个层级拥有的事件分发的相关方法进行整理：
| 事件分发相关方法 | 方法功能 | Activity | ViewGroup | View |
|---|---|---|---|---|
| public boolean dispatchTouchEvent | 事件分发 | + | + | + |
| public boolean onInterceptTouchEvent | 事件拦截 | + | ||
| public boolean onTouchEvent | 事件消费 | + | + | + |
view因为没有孩子，没有onInterceptTouchEvent
onTouchEvent中对点击事件的具体处理流程大概如下，只要View的CLICKABLE和LONG_CLICKABLE有一个为true，那么它就会消耗事件，返回true。总的来说，View的可不可用不影响是否消耗事件，只要clickable或者longClickable有一个为true，那么它就会消耗事件。
ViewGroup默认不拦截任何事件，因为从源码中可以看到ViewGroup的onInterceptTouchEvent方法默认返回false.
由View中dispatchTouchEvent可知，如果一个控件是可点击的，那么点击该控件时，dispatchTouchEvent的返回值必定是true
public boolean dispatchTouchEvent(MotionEvent event) {
if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
mOnTouchListener.onTouch(this, event)) {
return true;
}
return onTouchEvent(event);
}
- ViewGroup中dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent ev) {
final int action = ev.getAction();
final float xf = ev.getX();
final float yf = ev.getY();
final float scrolledXFloat = xf + mScrollX;
final float scrolledYFloat = yf + mScrollY;
final Rect frame = mTempRect;
boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (action == MotionEvent.ACTION_DOWN) {
if (mMotionTarget != null) {
mMotionTarget = null;
}
if (disallowIntercept || !onInterceptTouchEvent(ev)) {
ev.setAction(MotionEvent.ACTION_DOWN);
final int scrolledXInt = (int) scrolledXFloat;
final int scrolledYInt = (int) scrolledYFloat;
final View[] children = mChildren;
final int count = mChildrenCount;
for (int i = count - 1; i >= 0; i--) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null) {
child.getHitRect(frame);
if (frame.contains(scrolledXInt, scrolledYInt)) {
final float xc = scrolledXFloat - child.mLeft;
final float yc = scrolledYFloat - child.mTop;
ev.setLocation(xc, yc);
child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
if (child.dispatchTouchEvent(ev)) {
mMotionTarget = child;
return true;
}
}
}
}
}
}
boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||
(action == MotionEvent.ACTION_CANCEL);
if (isUpOrCancel) {
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
final View target = mMotionTarget;
if (target == null) {
ev.setLocation(xf, yf);
if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
}
return super.dispatchTouchEvent(ev);
}
if (!disallowIntercept && onInterceptTouchEvent(ev)) {
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
ev.setAction(MotionEvent.ACTION_CANCEL);
ev.setLocation(xc, yc);
if (!target.dispatchTouchEvent(ev)) {
}
mMotionTarget = null;
return true;
}
if (isUpOrCancel) {
mMotionTarget = null;
}
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
ev.setLocation(xc, yc);
if ((target.mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
target.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
mMotionTarget = null;
}
return target.dispatchTouchEvent(ev);
}
子view的onTouchEvent如果默认false不消费的话，会交给上级的onTouchEvent
viewGroup如果onInterceptTouchEvent不拦截，继续交给子view
viewGroup如果dispatchTouchEvent返回true，消费掉会还给上级的onTouchEvent
如果上面的点你都清楚的话，说明对事件分发是有清楚认识的，那么接下来上图
