Android触摸事件的传递(七)-ViewGroup

了解更多,移步Android触摸事件传递机制系列详解
Android触摸事件的传递(六)-ViewRootImpl-->Activity

1 activity的dispatchTouchEvent方法

activityDialog都是Callback接口的具体实现,主要看activitydispatchTouchEvent方法,

public boolean dispatchTouchEvent(MotionEvent ev) {
        •••
        if (getWindow().superDispatchTouchEvent(ev)) {
            return true;
        }
        return onTouchEvent(ev);
}

首先调用PhoneWindowsuperDispatchTouchEvent方法,如果未处理才继续调用onTouchEvent方法

2 DecorView的superDispatchTouchEvent

WindowsuperDispatchTouchEvent是个抽象方法

public abstract boolean superDispatchTouchEvent(MotionEvent event);

找到window的实现类---PhoneWindow(wingdow的唯一实现)

public  boolean superDispatchTouchEvent(MotionEvent event){
  return mDecor.superDispatchTouchEvent(event);
};

直接调用DecorView的superDispatchTouchEvent

3 ViewGoup--dispatchTouchEvent

  • DecorView继承自FrameLayout且是父view,所以事件最终传递给了ViewGroup
  • DecorView一般就是当前底层容器(即setContentView所设置的View的父容器)
  • 通过Activity.getWindow().getDecorView();获得
    通过下面可以获得activity所设置的viewsetContentView设置的view是其一个子view
 ((ViewGroup)getWindow().getDecorView().findViewById(android.R.id.content)).getChildAt(0);
public boolean dispatchTouchEvent(MotionEvent ev) {
        //验证事件是否连续
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
        }
        //这个变量用于记录事件是否被处理完
        boolean handled = false;
        //过滤掉一些不合法的事件:当前的View的窗口被遮挡了。
        if (onFilterTouchEventForSecurity(ev)) {
            //如果事件发生的View在的窗口,没有被遮挡
            final int action = ev.getAction();
            //重置前面为0 ,只留下后八位,用于判断相等时候,可以提高性能。
            final int actionMasked = action & MotionEvent.ACTION_MASK;
            //判断是不是Down事件,如果是的话,就要做初始化操作
            if (actionMasked == MotionEvent.ACTION_DOWN) {
                //如果是down事件,就要清空掉之前的状态,比如,重置手势判断什么的。
                //比如,之前正在判断是不是一个单点的滑动,但是第二个down来了,就表示,不可能是单点的滑动,要重新开始判断触摸的手势
                //清空掉mFirstTouchTarget
                // Throw away all previous state when starting a new touch gesture.
                // The framework may have dropped the up or cancel event for the previous gesture
                // due to an app switch, ANR, or some other state change.
                cancelAndClearTouchTargets(ev);
                resetTouchState();
            }
 
 
            //检查是否拦截事件
            final boolean intercepted;
            //如果当前是Down事件,或者已经有处理Touch事件的目标了
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                //判断允不允许这个View拦截
                //使用与运算作为判断,可以让我们在flag中,存储好几个标志
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
                //如果说允许拦截事件
                if (!disallowIntercept) {
                    //确定是不是拦截了
                    intercepted = onInterceptTouchEvent(ev);
                    //重新恢复Action,以免action在上面的步骤被人为地改变了
                    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.
                //如果说,事件已经初始化过了,并且没有子View被分配处理,那么就说明,这个ViewGroup已经拦截了这个事件
                intercepted = true;
            }
 
            // Check for cancelation.
            //如果viewFlag被设置了PFLAG_CANCEL_NEXT_UP_EVENT ,那么就表示,下一步应该是Cancel事件
            //或者如果当前的Action为取消,那么当前事件应该就是取消了。
            final boolean canceled = resetCancelNextUpFlag(this)
                    || actionMasked == MotionEvent.ACTION_CANCEL;
 
            // Update list of touch targets for pointer down, if needed.
            //如果需要(不是取消,也没有被拦截)的话,那么在触摸down事件的时候更新触摸目标列表
            //split代表,当前的ViewGroup是不是支持分割MotionEvent到不同的View当中
            final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
            //新的触摸对象,
            TouchTarget newTouchTarget = null;
            //是否把事件分配给了新的触摸
            boolean alreadyDispatchedToNewTouchTarget = false;
            //事件不是取消事件,也没有拦截那么就要判断
            if (!canceled && !intercepted) {
                //如果是个全新的Down事件
                //或者是有新的触摸点
                //或者是光标来回移动事件(不太明白什么时候发生)
                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                    //这个事件的索引,也就是第几个事件,如果是down事件就是0
                    final int actionIndex = ev.getActionIndex(); // always 0 for down
                    //获取分配的ID的bit数量
                    final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                            : TouchTarget.ALL_POINTER_IDS;
 
                    // Clean up earlier touch targets for this pointer id in case they
                    // have become out of sync.
                    //清理之前触摸这个指针标识,以防他们的目标变得不同步。
                    removePointersFromTouchTargets(idBitsToAssign);
 
                    final int childrenCount = mChildrenCount;
                    //如果新的触摸对象为null(这个不是铁定的吗)并且当前ViewGroup有子元素
                    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.
                        //下面所做的工作,就是找到可以接收这个事件的子元素
                        final View[] children = mChildren;
                        //是否使用自定义的顺序来添加控件
                        final boolean customOrder = isChildrenDrawingOrderEnabled();
                        for (int i = childrenCount - 1; i >= 0; i--) {
                            //如果是用了自定义的顺序来添加控件,那么绘制的View的顺序和mChildren的顺序是不一样的
                            //所以要根据getChildDrawingOrder取出真正的绘制的View
                            //自定义的绘制,可能第一个会画到第三个,和第四个,第二个画到第一个,这样里面的内容和Children是不一样的
                            final int childIndex = customOrder ?
                                    getChildDrawingOrder(childrenCount, i) : i;
                            final View child = children[childIndex];
                            //如果child不可以接收这个触摸的事件,或者触摸事件发生的位置不在这个View的范围内
                            if (!canViewReceivePointerEvents(child)
                                    || !isTransformedTouchPointInView(x, y, child, null)) {
                                continue;
                            }
                            //获取新的触摸对象,如果当前的子View在之前的触摸目标的列表当中就返回touchTarget
                            //子View不在之前的触摸目标列表那么就返回null
                            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.
                                //如果新的触摸目标对象不为空,那么就把这个触摸的ID赋予它,这样子,
                                //这个触摸的目标对象的id就含有了好几个pointer的ID了
 
                                newTouchTarget.pointerIdBits |= idBitsToAssign;
                                break;
                            }
                            //如果子View不在之前的触摸目标列表中,先重置childView的标志,去除掉CACEL的标志
                            resetCancelNextUpFlag(child);
                            //调用子View的dispatchTouchEvent,并且把pointer的id 赋予进去
                            //如果说,子View接收并且处理了这个事件,那么就更新上一次触摸事件的信息,
                            //并且为创建一个新的触摸目标对象,并且绑定这个子View和Pointer的ID
                            if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                                // Child wants to receive touch within its bounds.
                                mLastTouchDownTime = ev.getDownTime();
                                mLastTouchDownIndex = childIndex;
                                mLastTouchDownX = ev.getX();
                                mLastTouchDownY = ev.getY();
                                //这里给mFirstTouchTarget赋值
                                newTouchTarget = addTouchTarget(child, idBitsToAssign);
                                alreadyDispatchedToNewTouchTarget = true;
                                break;
                            }
                        }
                    }
                    //如果newTouchTarget为null,就代表,这个事件没有找到子View去处理它,
                    //那么,如果之前已经有了触摸对象(比如,我点了一张图,另一个手指在外面图的外面点下去)
                    //那么就把这个之前那个触摸目标定为第一个触摸对象,并且把这个触摸(pointer)分配给最近添加的触摸目标
                    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;
                    }
                }
            }
 
            // Dispatch to touch targets.
            //如果没有触摸目标
            if (mFirstTouchTarget == null) {
                // No touch targets so treat this as an ordinary view.
                //那么就表示我们要自己在这个ViewGroup处理这个触摸事件了
                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;
                //遍历TouchTargt树.分发事件,如果我们已经分发给了新的TouchTarget那么我们就不再分发给newTouchTarget
                while (target != null) {
                    final TouchTarget next = target.next;
                    if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                        handled = true;
                    } else {
                        //是否让child取消处理事件,如果为true,就会分发给child一个ACTION_CANCEL事件
                        final boolean cancelChild = resetCancelNextUpFlag(target.child)
                                || intercepted;
                        //派发事件
                        if (dispatchTransformedTouchEvent(ev, cancelChild,
                                target.child, target.pointerIdBits)) {
                            handled = true;
                        }
                        //cancelChild也就是说,派发给了当前child一个ACTION_CANCEL事件,
                        //那么就移除这个child
                        if (cancelChild) {
                            //没有父节点,也就是当前是第一个TouchTarget
                            //那么就把头去掉
                            if (predecessor == null) {
                                mFirstTouchTarget = next;
                            } else {
                                //把下一个赋予父节点的上一个,这样当前节点就被丢弃了
                                predecessor.next = next;
                            }
                            //回收内存
                            target.recycle();
                            //把下一个赋予现在
                            target = next;
                            //下面的两行不执行了,因为我们已经做了链表的操作了。
                            //主要是我们不能执行predecessor=target,因为删除本节点的话,父节点还是父节点
                            continue;
                        }
                    }
                    //如果没有删除本节点,那么下一轮父节点就是当前节点,下一个节点也是下一轮的当前节点
                    predecessor = target;
                    target = next;
                }
            }
 
            // Update list of touch targets for pointer up or cancel, if needed.
            //遇到了取消事件、或者是单点触摸下情况下手指离开,我们就要更新触摸的状态
            if (canceled
                    || actionMasked == MotionEvent.ACTION_UP
                    || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                resetTouchState();
            } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
                //如果是多点触摸下的手指抬起事件,就要根据idBit从TouchTarget中移除掉对应的Pointer(触摸点)
                final int actionIndex = ev.getActionIndex();
                final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
                removePointersFromTouchTargets(idBitsToRemove);
            }
        }
 
        if (!handled && mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
        }
        return handled;
    }

3.1 解析一:检查是否拦截事件

  • viewgroup会在两种情况下会判断是否要拦截当前事件:事件类型为ACTION_DOWN或者 mFirstTouchTarget != null
  • 当事件交由viewgroup的子元素处理时,mFirstTouchTarget被赋值并指向子元素,事件传递给子元素时才不为null。

通常

  • ACTION_DOWN的时候mFirstTouchTarget 还是null
  • ACTION_DOWN后面的事件mFirstTouchTarget不为null
  • ACTION_DOWN后面的事件mFirstTouchTargetnullviewgroup默认拦截 。
  • onInterceptTouchEvent默认返回false,viewgroup`默认不拦截

            //检查是否拦截事件
            final boolean intercepted;
            //如果当前是Down事件,或者已经有处理Touch事件的目标了
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                //判断允不允许这个View拦截
                //使用与运算作为判断,可以让我们在flag中,存储好几个标志
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
                //如果说允许拦截事件
                if (!disallowIntercept) {
                    //确定是不是拦截了
                    intercepted = onInterceptTouchEvent(ev);
                    //重新恢复Action,以免action在上面的步骤被人为地改变了
                    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.
                //如果说,事件已经初始化过了,并且没有子View被分配处理,那么就说明,这个ViewGroup已经拦截了这个事件
                intercepted = true;
            }

onInterceptTouchEvent默认返回false

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

3.2 检查子view并传递事件

  1. 判断事件不是取消事件,也没有拦截if (!canceled && !intercepted) {***}
  2. 判断child可不可以接收这个触摸的事件,或者触摸事件发生的位置在不在这个View的范围内
  3. 条件通过该子view 则赋值给newTouchTarget
  4. dispatchTransformedTouchEvent调用子View的dispatchTouchEvent,并且把pointer的id 赋予进去.如果说,子View接收并且处理了这个事件。如果返回true,则 alreadyDispatchedToNewTouchTarget = true;//已经消费事件并跳出循环。否则继续遍历循环。

            //事件不是取消事件,也没有拦截那么就要判断
            if (!canceled && !intercepted) {
                //如果是个全新的Down事件
                //或者是有新的触摸点
                //或者是光标来回移动事件(不太明白什么时候发生)
                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                    //这个事件的索引,也就是第几个事件,如果是down事件就是0
                    final int actionIndex = ev.getActionIndex(); // always 0 for down
                    //获取分配的ID的bit数量
                    final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                            : TouchTarget.ALL_POINTER_IDS;
 
                    // Clean up earlier touch targets for this pointer id in case they
                    // have become out of sync.
                    //清理之前触摸这个指针标识,以防他们的目标变得不同步。
                    removePointersFromTouchTargets(idBitsToAssign);
 
                    final int childrenCount = mChildrenCount;
                    //如果新的触摸对象为null(这个不是铁定的吗)并且当前ViewGroup有子元素
                    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.
                        //下面所做的工作,就是找到可以接收这个事件的子元素
                        final View[] children = mChildren;
                        //是否使用自定义的顺序来添加控件
                        final boolean customOrder = isChildrenDrawingOrderEnabled();
                        for (int i = childrenCount - 1; i >= 0; i--) {
                            //如果是用了自定义的顺序来添加控件,那么绘制的View的顺序和mChildren的顺序是不一样的
                            //所以要根据getChildDrawingOrder取出真正的绘制的View
                            //自定义的绘制,可能第一个会画到第三个,和第四个,第二个画到第一个,这样里面的内容和Children是不一样的
                            final int childIndex = customOrder ?
                                    getChildDrawingOrder(childrenCount, i) : i;
                            final View child = children[childIndex];
                            //如果child不可以接收这个触摸的事件,或者触摸事件发生的位置不在这个View的范围内
                            if (!canViewReceivePointerEvents(child)
                                    || !isTransformedTouchPointInView(x, y, child, null)) {
                                continue;
                            }
                            //获取新的触摸对象,如果当前的子View在之前的触摸目标的列表当中就返回touchTarget
                            //子View不在之前的触摸目标列表那么就返回null
                            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.
                                //如果新的触摸目标对象不为空,那么就把这个触摸的ID赋予它,这样子,
                                //这个触摸的目标对象的id就含有了好几个pointer的ID了
 
                                newTouchTarget.pointerIdBits |= idBitsToAssign;
                                break;
                            }
                            //如果子View不在之前的触摸目标列表中,先重置childView的标志,去除掉CACEL的标志
                            resetCancelNextUpFlag(child);
                            //调用子View的dispatchTouchEvent,并且把pointer的id 赋予进去
                            //如果说,子View接收并且处理了这个事件,那么就更新上一次触摸事件的信息,
                            //并且为创建一个新的触摸目标对象,并且绑定这个子View和Pointer的ID
                            if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                                // Child wants to receive touch within its bounds.
                                mLastTouchDownTime = ev.getDownTime();
                                mLastTouchDownIndex = childIndex;
                                mLastTouchDownX = ev.getX();
                                mLastTouchDownY = ev.getY();
                                //这里给mFirstTouchTarget赋值
                                newTouchTarget = addTouchTarget(child, idBitsToAssign);
                                alreadyDispatchedToNewTouchTarget = true;
                                break;
                            }
                        }
                    }
                    //如果newTouchTarget为null,就代表,这个事件没有找到子View去处理它,
                    //那么,如果之前已经有了触摸对象(比如,我点了一张图,另一个手指在外面图的外面点下去)
                    //那么就把这个之前那个触摸目标定为第一个触摸对象,并且把这个触摸(pointer)分配给最近添加的触摸目标
                    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;
                    }
                }
            }

3.3 自己处理事件

  1. 如果没有触摸目标那么就表示我们要自己在这个ViewGroup处理这个触摸事件了
    handled = dispatchTransformedTouchEvent(ev, canceled, null,TouchTarget.ALL_POINTER_IDS);
  • 注:如果检查子view没有消费掉事件
  1. 如果有 则遍历TouchTargt树分发事件,如果我们已经分发给了新的TouchTarget那么我们就不再分发给newTouchTarget if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {handled = true;}否则是否让child取消处理事件,如果为true,就会分发给child一个ACTION_CANCEL事件

            // Dispatch to touch targets.
            //如果没有触摸目标
            if (mFirstTouchTarget == null) {
                // No touch targets so treat this as an ordinary view.
                //那么就表示我们要自己在这个ViewGroup处理这个触摸事件了
                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;
                //遍历TouchTargt树.分发事件,如果我们已经分发给了新的TouchTarget那么我们就不再分发给newTouchTarget
                while (target != null) {
                    final TouchTarget next = target.next;
                    if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                        handled = true;
                    } else {
                        //是否让child取消处理事件,如果为true,就会分发给child一个ACTION_CANCEL事件
                        final boolean cancelChild = resetCancelNextUpFlag(target.child)
                                || intercepted;
                        //派发事件
                        if (dispatchTransformedTouchEvent(ev, cancelChild,
                                target.child, target.pointerIdBits)) {
                            handled = true;
                        }
                        //cancelChild也就是说,派发给了当前child一个ACTION_CANCEL事件,
                        //那么就移除这个child
                        if (cancelChild) {
                            //没有父节点,也就是当前是第一个TouchTarget
                            //那么就把头去掉
                            if (predecessor == null) {
                                mFirstTouchTarget = next;
                            } else {
                                //把下一个赋予父节点的上一个,这样当前节点就被丢弃了
                                predecessor.next = next;
                            }
                            //回收内存
                            target.recycle();
                            //把下一个赋予现在
                            target = next;
                            //下面的两行不执行了,因为我们已经做了链表的操作了。
                            //主要是我们不能执行predecessor=target,因为删除本节点的话,父节点还是父节点
                            continue;
                        }
                    }
                    //如果没有删除本节点,那么下一轮父节点就是当前节点,下一个节点也是下一轮的当前节点
                    predecessor = target;
                    target = next;
                }
            }

3.4 dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,View child, int desiredPointerIdBits)

  • 通过以上代码可知
  1. 对于目标子view调用如dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)
  2. ViewGroup自己处理事件调用 dispatchTransformedTouchEvent(ev, canceled, null,TouchTarget.ALL_POINTER_IDS);
  3. 当让child取消处理事件,如果为true,就会分发给child一个ACTION_CANCEL事件。调用dispatchTransformedTouchEvent(ev, cancelChild,target.child, target.pointerIdBits)
    可以看出 在ViewGroup自己处理时child为null。其他child不为null。
    dispatchTransformedTouchEvent
    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;
        }

        // Calculate the number of pointers to deliver.
        final int oldPointerIdBits = event.getPointerIdBits();
        final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;

        // If for some reason we ended up in an inconsistent state where it looks like we
        // might produce a motion event with no pointers in it, then drop the event.
        if (newPointerIdBits == 0) {
            return false;
        }

        // If the number of pointers is the same and we don't need to perform any fancy
        // irreversible transformations, then we can reuse the motion event for this
        // dispatch as long as we are careful to revert any changes we make.
        // Otherwise we need to make a copy.
        final MotionEvent transformedEvent;
        if (newPointerIdBits == oldPointerIdBits) {
            if (child == null || child.hasIdentityMatrix()) {
                if (child == null) {
                    handled = super.dispatchTouchEvent(event);
                } else {
                    final float offsetX = mScrollX - child.mLeft;
                    final float offsetY = mScrollY - child.mTop;
                    event.offsetLocation(offsetX, offsetY);

                    handled = child.dispatchTouchEvent(event);

                    event.offsetLocation(-offsetX, -offsetY);
                }
                return handled;
            }
            transformedEvent = MotionEvent.obtain(event);
        } else {
            transformedEvent = event.split(newPointerIdBits);
        }

        // Perform any necessary transformations and dispatch.
        if (child == null) {
            handled = super.dispatchTouchEvent(transformedEvent);
        } else {
            final float offsetX = mScrollX - child.mLeft;
            final float offsetY = mScrollY - child.mTop;
            transformedEvent.offsetLocation(offsetX, offsetY);
            if (! child.hasIdentityMatrix()) {
                transformedEvent.transform(child.getInverseMatrix());
            }

            handled = child.dispatchTouchEvent(transformedEvent);
        }

        // Done.
        transformedEvent.recycle();
        return handled;
    }
  • 通过查看dispatchTransformedTouchEvent可以看出当childnull时调用super.dispatchTouchEvent(event);child不为null时调用child.dispatchTouchEvent(event)
  • 由此可以看出ViewGroup或子view自身真正处理事件时都是通过View的dispatchTouchEvent分发下去的。

参考

View的事件分发机制——dispatchTouchEvent详解

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