Android事件分发-View、ViewGroup、Activity源码处理

在看事件分发之前，先看一下View、ViewGroup、Activity的对Touch事件的处理。

一、View对Touch事件的处理

    public boolean dispatchTouchEvent(MotionEvent event) {
       ...   
     boolean result = false;
     
     if (li != null && li.mOnTouchListener != null
                && (mViewFlags & ENABLED_MASK) == ENABLED
                && li.mOnTouchListener.onTouch(this, event)) {//平常常用的onTouch监听事件
            result = true;
        }
        
        //这里调用了自身的onTouchEvent(event)
        if (!result && onTouchEvent(event)) {
            result = true;
        }
    return result;
}

一句话：View 的dispatchTouchEvent()中调用了onTouchEvent(event)。
看下View的onTouchEvent()是如何处理的:

 public boolean onTouchEvent(MotionEvent event) {
  ...
  if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
            switch (action) {
                    case MotionEvent.ACTION_UP:
                     performClick();//点击事件
                      break;
            }

  }
}

View的事件分发处理.png

二、ViewGroup对Touch事件的处理

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    .....
    boolean handled = false;
    if (onFilterTouchEventForSecurity(ev)) {
        ...
        // Check for interception.
        final boolean intercepted;
        if (actionMasked == MotionEvent.ACTION_DOWN
                || mFirstTouchTarget != null) {
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
            if (!disallowIntercept) {
                intercepted = onInterceptTouchEvent(ev);//是否拦截事件
                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;
        }
        ....
        // Dispatch to touch targets.
        if (mFirstTouchTarget == null) {//没有child View

            // No touch targets so treat this as an ordinary view.
            handled = dispatchTransformedTouchEvent(ev, canceled, null,
                    TouchTarget.ALL_POINTER_IDS);
        } else {
            // Dispatch to touch targets, excluding the new touch target if we already
            // dispatched to it.  Cancel touch targets if necessary.
            TouchTarget predecessor = null;
            TouchTarget target = mFirstTouchTarget;
            while (target != null) {
                final TouchTarget next = target.next;
                if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                    handled = true;
                } else {
                    final boolean cancelChild = resetCancelNextUpFlag(target.child)
                            || intercepted;
                     // 有child View ，事件分发到child View     
                    if (dispatchTransformedTouchEvent(ev, cancelChild,
                            target.child, target.pointerIdBits)) {
                        handled = true;
                    }
                    ....
                }
                predecessor = target;
                target = next;
            }
        }
        ...
    }
    ...
    return handled;
}

看一下dispatchTransformedTouchEvent()方法

boolean dispatchTransformedTouchEvent{
    .....    
    if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
        event.setAction(MotionEvent.ACTION_CANCEL);
        
        if (child == null) {//没有child View
            handled = super.dispatchTouchEvent(event);
        } else {// 有childView 时调用了child View的dispatchTouchEvent(event)
            handled = child.dispatchTouchEvent(event);
        }
        event.setAction(oldAction);
        return handled;
    }    
}

onInterceptTouchEvent()方法默认返回false

public boolean onInterceptTouchEvent(MotionEvent ev) {
    return false;
}

总结：ViewGroup 继承 View，先调用onInterceptTouchEvent(ev)判断是否拦截事件(默认返回false)，如果不拦截，有child view就调用child view的dispatchTouchEvent()，没有就调用父类即View.dispatchTouchEvent(event)。

ViewGroup的事件分发处理.png

三、Activity对Touch事件的处理

public boolean dispatchTouchEvent(MotionEvent ev) {
    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        onUserInteraction();
    }
    //将触摸事件传递更深地View视图层。
    if (getWindow().superDispatchTouchEvent(ev)) {
        return true;
    }
    return onTouchEvent(ev);
}

调用getWindow().superDispatchTouchEvent(ev)，将触摸事件传递更深地View视图层。
从这里可以看出来，Activity的root view 消费掉了Touch事件，Activity的onTouchEvent()就不会被执行。

public boolean onTouchEvent(MotionEvent event) {
    if (mWindow.shouldCloseOnTouch(this, event)) {
        finish();
        return true;
    }

    return false;
}

getWindow()返回的是PhoneWindow 对象。PhoneWindow继承Window

看一下PhoneWindow的superDispatchTouchEvent()方法。

// This is the top-level view of the window, containing the window decor.
private DecorView mDecor;
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
    boolean handled = mDecor.superDispatchTouchEvent(event);
    }
    return handled;
}

DecorView 继承了 FrameLayout，也就是说DecorView就是个ViewGroup。

一句话：Activity的onTouchEvent()是否执行，就看root view的Touch事件是否被消费。

Activity的事件分发处理.png

以上记录都是学习记录，有什么错误的地方，希望指正！！ViewGroup的事件分发理解的有些模糊。