舌尖上的安卓(android触控事件机制学习笔记录)

 @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
        }


        // Check for interception.
        final boolean intercepted;//拦截的标记变量
        if (actionMasked == MotionEvent.ACTION_DOWN
                || mFirstTouchTarget != null) {
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
            if (!disallowIntercept) {
            
                //调用自身的 onInterceptTochEvent，判断是否需要拦截
                intercepted = onInterceptTochEvent(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;
        }


        
        //假如没拦截
        if (!canceled && !intercepted) {
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                    || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {

                if (newTouchTarget == null && childrenCount != 0) {
                    final float x = ev.getX(actionIndex);
                    final float y = ev.getY(actionIndex);
                    // Find a child that can receive the event.
                    // Scan children from front to back.
                    final View[] children = mChildren;

                    final boolean customOrder = isChildrenDrawingOrderEnabled();
                    //遍历所有的子View，并且调用他们的事件分发方法dispatchTouchEvent()

                    for (int i = childrenCount - 1; i >= 0; i--) {                      final int childIndex = customOrder ?
                                getChildDrawingOrder(childrenCount, i) : i;
                        final View child = children[childIndex];
                        if (!canViewReceivePointerEvents(child)
                                || !isTransformedTouchPointInView(x, y, child, null)) {
                            continue;
                        }

                        newTouchTarget = getTouchTarget(child);
                        //newTouchTarget表示事件传递的View目标，当不为空的时候，直接跳出循环
                        if (newTouchTarget != null) {
                          
                            newTouchTarget.pointerIdBits |= idBitsToAssign;
                            break;
                        }

                        resetCancelNextUpFlag(child);
                        //递归调用子View分发事件方法，
                        if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { 
                            
                            mLastTouchDownTime = ev.getDownTime();
                            mLastTouchDownIndex = childIndex;
                            mLastTouchDownX = ev.getX();
                            mLastTouchDownY = ev.getY();
                            //设置分发目标newTouchTarget为当前View
                            newTouchTarget = addTouchTarget(child, idBitsToAssign);
                            //标记子View的分发结果，为True的话，下面的代码是不会调用当前View的onTouch方法的，也就是规则1生成的原因
                            alreadyDispatchedToNewTouchTarget = true;
                            break;
                        }
                    }
                }

            }
        }
        
        
        
        
        if (mFirstTouchTarget == null) {
            // 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;
                
                //如果刚才alreadyDispatchedToNewTouchTarget设为True的话，就不执行下面的dispatchTransformedTouchEvent
                //alreadyDispatchedToNewTouchTarget是由子View的onTouch返回值决定的，
                
                if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                    handled = true;
                } else {
                    final boolean cancelChild = resetCancelNextUpFlag(target.child)
                            || intercepted;
                    
                    //执行自身的Touch事件，
                    if (dispatchTransformedTouchEvent(ev, cancelChild,
                            target.child, target.pointerIdBits)) {
                        handled = true;
                    }
                    if (cancelChild) {
                        if (predecessor == null) {
                            mFirstTouchTarget = next;
                        } else {
                            predecessor.next = next;
                        }
                        target.recycle();
                        target = next;
                        continue;
                    }
                }
                predecessor = target;
                target = next;
            }
        }
    }

public boolean dispatchTouchEvent(MotionEvent event) {
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(event, 0);
        }
//...
        if (onTouchEvent(event)) {//View的dispatchTouchEvent十分简单，就是调用下自己onTouch事件，并且返回结果。这个结果直接影响以后的事件是否///继续传递

            return true;
        }
    }
//...
    return false;
}