【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 五 )（二）

@Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
      // 设置父容器是否要拦截子组件的触摸事件
        if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
            // We're already in this state, assume our ancestors are too
            return;
        }
        if (disallowIntercept) {
            mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
        } else {
            mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
        }
        // Pass it up to our parent
        if (mParent != null) {
            mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
        }
    }

// 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);
                    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;
            }

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;
        }
        ...
  }

@UiThread
public abstract class ViewGroup extends View implements ViewParent, ViewManager {
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
  ...
      // 如果上述事件分发方法 dispatchTransformedTouchEvent 返回 true 
      // 就会创建 newTouchTarget 值 , 该值不会为空 , 同时 mFirstTouchTarget 不为空
      // 如果上述事件分发方法 dispatchTransformedTouchEvent 返回 false 
      // 此时 newTouchTarget 值 , 就会为空 , 同时 mFirstTouchTarget 为空 
                    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;
                    }
                }
            }
    // 如果事件被消费 , 事件分发方法 dispatchTransformedTouchEvent 返回 true 
    // 就会创建 newTouchTarget 值 , 该值不会为空 , 同时 mFirstTouchTarget 不为空
    // 反之
    // 如果上述事件分发方法 dispatchTransformedTouchEvent 返回 false 
    // 此时 newTouchTarget 值 , 就会为空 , 同时 mFirstTouchTarget 为空 
    // 
    // 还有一个逻辑就是 , 如果该事件被父容器拦截 , mFirstTouchTarget 也是 null 值
    // 调用 dispatchTransformedTouchEvent , 但是传入的子组件时 null 
    // 在 dispatchTransformedTouchEvent 方法中触发调用 if (child == null) 分支的 
    // handled = super.dispatchTouchEvent(event) 方法 , 调用父类的事件分发方法 
            // Dispatch to touch targets.
            if (mFirstTouchTarget == null) {
              // 事件没有被消费的分支 
                // No touch targets so treat this as an ordinary view.
                handled = dispatchTransformedTouchEvent(ev, canceled, null,
                        TouchTarget.ALL_POINTER_IDS);
            }
  ...
  }
    /**
     * Adds a touch target for specified child to the beginning of the list.
     * Assumes the target child is not already present.
     */
    private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
        final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
        target.next = mFirstTouchTarget;
        mFirstTouchTarget = target;
        return target;
    }
    /**
     * Transforms a motion event into the coordinate space of a particular child view,
     * filters out irrelevant pointer ids, and overrides its action if necessary.
     * If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
     */
    private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
            View child, int desiredPointerIdBits) {
        final boolean handled;
        // Canceling motions is a special case.  We don't need to perform any transformations
        // or filtering.  The important part is the action, not the contents.
        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;
        }
        ...
  }
}