Android事件分发详解(三)——ViewGroup的dispatchTouchEvent()源码学习

package cc.aa;import android.os.Environment;import android.view.MotionEvent;import android.view.View;public class UnderstandDispatchTouchEvent {    /**     * 该示例的重点:     * 1 ViewGroup的dispatchTouchEvent()源码学习及其注释     * 2 ViewGroup的dispatchTransformedTouchEvent()源码学习及其注释     * 3 弄明白两个问题:     *   (1)为什么某个子View对于ACTION_DOWN返回false,那么系统不会讲ACTION_MOVE和ACTION_UP派发给该子View.     *   因为ACTION_DOWN是一系列Touch事件的开端,如果子View对于该ACTION_DOWN事件在onTouchEvent()中返回了false即未消费.     *   那么ViewGroup就不会把后续的ACTION_MOVE和ACTION_UP派发给该子View.在这种情况下ViewGroup就和普通的View一样了,     *   调用该ViewGroup自己的dispatchTouchEvent()从而调用自己的onTouchEvent();即不会将事件分发给子View.     *   详细代码请参见如下代码分析.     *        *   (2)为什么子view对于Touch事件处理返回true那么其上层的ViewGroup就无法处理Touch事件了     *   这个想必大家都知道了,因为该Touch事件被子View消费了其上层的ViewGroup就无法处理该Touch事件了.     *   那么在源码中的依据是什么呢?请看下面的源码分析     *        *      * 常说事件传递中的流程是:     * dispatchTouchEvent->onInterceptTouchEvent->onTouchEvent     * 在这个链条中dispatchTouchEvent()是处在链首的位置当然也是最重要的.     * 在dispatchTouchEvent()决定了Touch事件是由自己的onTouchEvent()处理     * 还是分发给子View处理让子View调用其自身的dispatchTouchEvent()处理.     *      *      * 其实dispatchTouchEvent()和onInterceptTouchEvent()以及onTouchEvent()的关系     * 在dispatchTouchEvent()方法的源码中体现得很明显.     * 比如dispatchTouchEvent()会调用onInterceptTouchEvent()来判断是否要拦截.     * 比如dispatchTouchEvent()会调用dispatchTransformedTouchEvent()方法且在该方法中递归调用     * dispatchTouchEvent();从而会在dispatchTouchEvent()里最终调用到onTouchEvent()     *      *      *      *        * 参考资料:     * 0 http://blog.csdn.net/sahadev_/article/details/23839039     * 1 http://wangkuiwu.github.io/2015/01/04/TouchEvent-ViewGroup/     * 2 http://www.cnblogs.com/xiaoweiz/p/3838682.html     * 3 http://hukai.me/android-deeper-touch-event-dispatch-process/     * 4 http://blog.csdn.net/yanbober/article/details/45912661     * 5 http://www.eoeandroid.com/thread-542296-1-1.html     * 6 http://www.eoeandroid.com/forum.php?mod=viewthread&tid=319301     * 7 http://stackvoid.com/details-dispatch-onTouch-Event-in-Android/     *   Thank you very much     */    @Override    public boolean dispatchTouchEvent(MotionEvent ev) {        if (mInputEventConsistencyVerifier != null) {            mInputEventConsistencyVerifier.onTouchEvent(ev, 1);        }        boolean handled = false;        if (onFilterTouchEventForSecurity(ev)) {            final int action = ev.getAction();            final int actionMasked = action & MotionEvent.ACTION_MASK;            /**             * 第一步:对于ACTION_DOWN进行处理(Handle an initial down)             * 因为ACTION_DOWN是一系列事件的开端,当是ACTION_DOWN时进行一些初始化操作.             * 从源码的注释也可以看出来:清除以往的Touch状态(state)开始新的手势(gesture)             * cancelAndClearTouchTargets(ev)中有一个非常重要的操作:             * 将mFirstTouchTarget设置为null!!!!             * 随后在resetTouchState()中重置Touch状态标识             */            if (actionMasked == MotionEvent.ACTION_DOWN) {                // 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();            }            /** * 第二步:检查是否要拦截(Check for interception) * 在哪些情况下会调用该代码呢？有如下几种情况 * 1 处理ACTION_DOWN事件 * 2 当ACTION_DOWN事件被子View消费后处理ACTION_MOVE和ACTION_UP时 *  会调用该代码。因为此时mFirstTouchTarget!=null。所以此时ViewGroup *  是有机会拦截ACTION_MOVE和ACTION_UP的,但是我们也可以调用方法: *  requestDisallowInterceptTouchEvent来禁止ViewGroup的事件拦截. *  如果子View没有消费Touch事件,那么那么当后续的ACTION_MOVE和ACTION_UP *  到来时是不会调用到本处代码的. *   * 在dispatchTouchEvent(MotionEventev)这一大段代码中 * 使用变量intercepted来标记ViewGroup是否拦截Touch事件的传递. * 该变量在后续代码中起着很重要的作用. *  * 从此处if(actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null)及其内部代码可知: * 当ViewGroup决定拦截事件后,那么后续的点击事件将会默认交给它处理,不再调用 * onInterceptTouchEvent()判断是否需要拦截. * 这个是为什么? * 因为在处理ACTION_DOWN时如果Touch事件被子View消费,那么mFirstTouchTarget不为空; * 反之,如果Touch事件没有被子View消费,那么mFirstTouchTarget为空,即此时Touch由当前 * 的ViewGroup拦截。此时当ACTION_MOVE和ACTION_UP来到时,不再满足: * if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) * 当然也就无法调用其内部的onInterceptTouchEvent()。 * 通俗地说:一旦ViewGroup拦截了ACTION_DOWN事件由自身的onTouchEvent()处理,那么 * 对于后续的ACTION_MOVE和ACTION_UP而言ViewGroup不再调用onInterceptTouchEvent() * 判断是否拦截. *  * 这里有个东西需要注意:FLAG_DISALLOW_INTERCEPT * 在子View中调用requestDisallowInterceptTouchEvent()后造成disallowIntercept为true * 即禁止拦截.于是不满足if(!disallowIntercept)所以也就调用不到该if内的onInterceptTouchEvent() * 自然就没有办法拦截了. * 但是requestDisallowInterceptTouchEvent()对于ACTION_DOWN是无效的. * 因为对于ACTION_DOWN会调用 cancelAndClearTouchTargets(ev)和resetTouchState(); * 对FLAG_DISALLOW_INTERCEPT等状态值复原重置(参考上面的代码) *  * 举两种情况说明: * 1 当处理ACTION_DOWN时当然会满足 *  if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) *  对于ACTION_DOWN子View有两种处理结果 *  1.1 消耗了Touch事件,那么mFirstTouchTarget不为null. *      所以处理后续的ACTION_MOVE和ACTION_UP时依然满足该if判断 *  1.2 没有消耗Touch事件.mFirstTouchTarget=null.不满足该if. *      所以后续的ACTION_MOVE和ACTION_UP由ViewGroup处理,此时再讨论什么拦截也就没有意义了. *      同样的道理当子View消费了ACTION_DOWN后当处理ACTION_MOVE的时候ViewGroup拦截了该事件 *      那么当ACTION_UP随之到来时由于mFirstTouchTarget=null所以不会再调用该段代码,自然也就 *      不会调用onInterceptTouchEvent()判断是否拦截了.这点在上面的注释也有提及 * 2 当出现1.1的情况时满足该if判断. *  如果在子View中调用了requestDisallowInterceptTouchEvent()那么就禁止拦截 *  即disallowIntercept=true.所以不满足if (!disallowIntercept)当然也就调用不到 *  onInterceptTouchEvent(ev)了,而是执行else{ intercepted = false;} *  也就是说ViewGroup无法拦截Touch了. */            final boolean intercepted;// 事件为ACTION_DOWN或者mFirstTouchTarget不为null(即已经找到能够接收touch事件的目标组件)时if成立            if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) {            //判断disallowIntercept(禁止拦截)标志位//因为在其他地方可能调用了requestDisallowInterceptTouchEvent()改变该值.//对于此方法的作用其实看requestDisallowInterceptTouchEvent()这个方法名就可明白了                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;                //当禁止拦截为false时(即disallowIntercept为false)调用onInterceptTouchEvent(ev)方法                if (!disallowIntercept) {                //既然disallowIntercept为false那么就调用onInterceptTouchEvent()方法将结果赋值给intercepted                //常说事件传递中的流程是:dispatchTouchEvent->onInterceptTouchEvent->onTouchEvent                //其实在这就是一个体现,在dispatchTouchEvent()中调用了onInterceptTouchEvent()                    intercepted = onInterceptTouchEvent(ev);                    ev.setAction(action); // restore action in case it was changed                } else {                //禁止拦截的FLAG为ture说明没有必要去执行是否需要拦截了能够顺利通过,所以设置拦截变量为false                //即当禁止拦截为true时(即disallowIntercept为true)设置intercepted = false                    intercepted = false;                }            } else {            //当事件不是ACTION_DOWN并且mFirstTouchTarget为null(即没有Touch的目标组件)时            //设置 intercepted = true表示ViewGroup执行Touch事件拦截的操作。                //There are no touch targets and this action is not an initial down                //so this view group continues to intercept touches.                intercepted = true;            }                        /**             * 第三步:检查cancel(Check for cancelation)             *              */            final boolean canceled = resetCancelNextUpFlag(this) || actionMasked == MotionEvent.ACTION_CANCEL;                        /**             * 第四步:事件分发(Update list of touch targets for pointer down, if needed)             */            final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;            TouchTarget newTouchTarget = null;            boolean alreadyDispatchedToNewTouchTarget = false;            //不是ACTION_CANCEL并且ViewGroup的拦截标志位intercepted为false(不拦截)            if (!canceled && !intercepted) {            //处理ACTION_DOWN事件.这个环节比较繁琐.                if (actionMasked == MotionEvent.ACTION_DOWN                    || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)                    || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {                    final int actionIndex = ev.getActionIndex(); // always 0 for down                    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.                    removePointersFromTouchTargets(idBitsToAssign);                    final int childrenCount = mChildrenCount;                    if (childrenCount != 0) {                    // 依据Touch坐标寻找子View来接收Touch事件                        // Find a child that can receive the event.                        // Scan children from front to back.                        final View[] children = mChildren;                        final float x = ev.getX(actionIndex);                        final float y = ev.getY(actionIndex);                        final boolean customOrder = isChildrenDrawingOrderEnabled();                        // 遍历子View判断哪个子View接受Touch事件                        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);                            if (newTouchTarget != null) {                            // 找到接收Touch事件的子View!!!!!!!即为newTouchTarget.                            // 既然已经找到了,所以执行break跳出for循环                                // Child is already receiving touch within its bounds.                                // Give it the new pointer in addition to the ones it is handling.                                newTouchTarget.pointerIdBits |= idBitsToAssign;                                break;                            }                            resetCancelNextUpFlag(child);                            /**                             * 如果上面的if不满足,当然也不会执行break语句.                             * 于是代码会执行到这里来.                             *                              *                              * 调用方法dispatchTransformedTouchEvent()将Touch事件传递给子View做                             * 递归处理(也就是遍历该子View的View树)                             * 该方法很重要,看一下源码中关于该方法的描述:                             * 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.                             * 将Touch事件传递给特定的子View.                             * 该方法十分重要!!!!!!!!!!!!!!!!!                             * 在该方法中为一个递归调用,会递归调用dispatchTouchEvent()方法!!!!!!!!!!                             * 在dispatchTouchEvent()中:                             * 如果子View为ViewGroup并且Touch没有被拦截那么递归调用dispatchTouchEvent()                             * 如果子View为View那么就会调用其onTouchEvent(),这个不再赘述.                             *                              *                              * 该方法返回true则表示子View消费掉该事件,同时进入该if判断.                             * 满足if语句后重要的操作有:                             * 1 给newTouchTarget赋值                             * 2 给alreadyDispatchedToNewTouchTarget赋值为true.                             *   看这个比较长的英语名字也可知其含义:已经将Touch派发给新的TouchTarget                             * 3 执行break.                             *   因为该for循环遍历子View判断哪个子View接受Touch事件,既然已经找到了                             *   那么就跳出该for循环.                             * 4 注意:                             *   如果dispatchTransformedTouchEvent()返回false即子View的onTouchEvent返回false                             *   (即Touch事件未被消费)那么就不满足该if条件.所以也就无法执行addTouchTarget().                             *   在此简单说一下addTouchTarget()中涉及到的ViewGroup的一个内部类TouchTarget——它是一个事件链.                             *   该处的mFirstTouchTarget就是一个TouchTarget.它保存了可以消耗Touch事件的View.                             *   在该处,如果dispatchTransformedTouchEvent()返回true即子View的onTouchEvent返回true则说明                             *   该View消耗了Touch事件,那么将该View加入到事件链中!!!!!!!!!!!!!!!                             *   尤其注意:                             *   这个操作是在处理ACTION_DOWN的代码块里进行的.即是在:                             *    if (actionMasked == MotionEvent.ACTION_DOWN||                              *    (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) ||                              *    actionMasked == MotionEvent.ACTION_HOVER_MOVE)                             *    这个大的if判断中处理的.                             *    当处理ACTION_MOVE事件和ACTION_UP事件的时候是不会进入这个if判断的!!!!!                             *    而是直接从去判断mFirstTouchTarget!!!!!!!!!!!!!!!!                             *    所以如果一个View不处理ACTION_DOWN那么该,那么该View是不会保存在mFirstTouchTarget                             *    中的,也就无法继续处理ACTION_MOVE事件和ACTION_UP事件!!!!!!!!!!即若该View不消耗                             *    ACTION_DOWN事件那么系统是不会讲ACTION_MOVE和ACTION_UP事件传给给该View的                             * 5 注意:                             *   如果dispatchTransformedTouchEvent()返回true即子View                             *   的onTouchEvent返回true(即Touch事件被消费)那么就满足该if条件.                             *   从而mFirstTouchTarget不为null!!!!!!!!!!!!!!!!!!!                             * 6 小结:                             *   对于此处ACTION_DOWN的处理具体体现在dispatchTransformedTouchEvent()                             *   该方法返回boolean,如下:                             *   true---->事件被消费----->mFirstTouchTarget!=null                             *   false--->事件未被消费--->mFirstTouchTarget==null                             *   因为在dispatchTransformedTouchEvent()会调用递归调用dispatchTouchEvent()和onTouchEvent()                             *   所以dispatchTransformedTouchEvent()的返回值实际上是由onTouchEvent()决定的.                             *                                *   简单地说onTouchEvent()是否消费了Touch事件(true or false)的返回值决定了                             *   dispatchTransformedTouchEvent()的返回值!!!!从而决定了mFirstTouchTarget是否为null!!!!!!                             *   从而进一步决定了ViewGroup是否处理Touch事件.这一点在下面的代码中很有体现.                             */                            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();                                //调用addTouchTarget()将child添加到mFirstTouchTarget链表的表头                                //注意在addTouchTarget()方法内部会对mFirstTouchTarget操作,使其不为null                                newTouchTarget = addTouchTarget(child, idBitsToAssign);                                alreadyDispatchedToNewTouchTarget = true;                                break;                            }                        }//for循环结束                    }                                        /**                     * 该if条件表示:                     * 经过前面的for循环没有找到子View接收Touch事件并且之前的mFirstTouchTarget不为空                     */                    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指向了最初的TouchTarget                        newTouchTarget.pointerIdBits |= idBitsToAssign;                    }//处理ACTION_DOWN结束                }            }                                    /**             * 经过上面对于ACTION_DOWN的处理后mFirstTouchTarget有两种情况:             * (当然如果不是ACTION_DOWN就不会经过上面较繁琐的流程而是从此处开始执行,比如ACTION_MOVE和ACTION_UP)             *              * 情况1 mFirstTouchTarget为null             *       即没有找到能够消费touch事件的子组件或者是touch事件被拦截了             * 情况2 mFirstTouchTarget不为null             *       即找到了能够消费touch事件的子组件则后续的touch事件都可以传递到子View             * 这两种情况的详细分析见下.             *              * 这两种情况下都会去调用方法:             * dispatchTransformedTouchEvent(MotionEvent event,boolean cancel,View child,int desiredPointerIdBits)             * 我们重点关注该方法的第三个参数View child.             * 详情请参加下面dispatchTransformedTouchEvent()源码分析             * 在该源码中解释了：             * 为什么子view对于Touch事件处理返回true那么其上层的ViewGroup就无法处理Touch事件了!!!!!!!!!             * 为什么子view对于Touch事件处理返回false那么其上层的ViewGroup才可以处理Touch事件!!!!!!!!!!             *              */            if (mFirstTouchTarget == null) {            /**             * 情况1：mFirstTouchTarget为null             *              * 经过上面的分析mFirstTouchTarget为null就是说Touch事件未被消费.             * 即没有找到能够消费touch事件的子组件或Touch事件被拦截了，             * 则调用ViewGroup的dispatchTransformedTouchEvent()方法处理Touch事件则和普通View一样.             * 即子View没有消费Touch事件,那么子View的上层ViewGroup才会调用其onTouchEvent()处理Touch事件.             * 在源码中的注释为:No touch targets so treat this as an ordinary view.             * 也就是说此时ViewGroup像一个普通的View那样调用dispatchTouchEvent(),且在dispatchTouchEvent()             * 中会去调用onTouchEvent()方法.             * 具体的说就是在调用dispatchTransformedTouchEvent()时第三个参数为null.             * 第三个参数View child为null会做什么样的处理呢?             * 请参见下面dispatchTransformedTouchEvent()的源码分析             */                handled = dispatchTransformedTouchEvent(ev, canceled, null,TouchTarget.ALL_POINTER_IDS);            } else {            /**             * 情况2：mFirstTouchTarget不为null             * 即找到了可以消费Touch事件的子View且后续Touch事件可以传递到该子View             * 在源码中的注释为:             * 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) {                    //如果前面利用ACTION_DOWN事件寻找符合接收条件的子组件的同时消费掉了ACTION_DOWN事件                    //那么这里为handled赋值为true                        handled = true;                    } else {                        final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted;                        //对于非ACTION_DOWN事件继续传递给目标子组件进行处理                        //依然是递归调用dispatchTransformedTouchEvent()                        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;                }            }            /**             * 处理ACTION_UP和ACTION_CANCEL             * Update list of touch targets for pointer up or cancel, if needed.             * 在此主要的操作是还原状态             */            if (canceled|| actionMasked == MotionEvent.ACTION_UP                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {                resetTouchState();            } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {                final int actionIndex = ev.getActionIndex();                final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);                removePointersFromTouchTargets(idBitsToRemove);            }        }        if (!handled && mInputEventConsistencyVerifier != null) {            mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);        }        return handled;    }                //=====================以上为dispatchTouchEvent()源码分析======================                                //===============以下为dispatchTransformedTouchEvent()源码分析=================        /**     * 在dispatchTouchEvent()中会调用dispatchTransformedTouchEvent()将事件分发给子View处理     *      * 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.     *      * 在此请着重注意第三个参数:View child     * 在dispatchTouchEvent()中多次调用dispatchTransformedTouchEvent(),但是有时候第三个参数为null,有时又不是.     * 那么这个参数是否为null有什么区别呢？     * 在如下dispatchTransformedTouchEvent()源码中可见多次对于child是否为null的判断,并且均做出如下类似的操作:     * if (child == null) {     *       handled = super.dispatchTouchEvent(event);     *    } else {     *       handled = child.dispatchTouchEvent(event);     * }     * 这个代码是什么意思呢?     *      * 当child == null时会将Touch事件传递给该ViewGroup自身的dispatchTouchEvent()处理.     * 即super.dispatchTouchEvent(event)     * 正如源码中的注释描述的一样:     * If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.     *      * 当child != null时会调用该子view(当然该view可能是一个View也可能是一个ViewGroup)的dispatchTouchEvent(event)处理.     * 即child.dispatchTouchEvent(event);     *      * 那么该child是否为null又是由什么决定的呢？     * 在dispatchTouchEvent()中已经知道了:     * 如果Touch事件被消耗掉那么child不为null     * 如果Touch事件未被消耗掉那么child为null     *      * 这就解释了：     * 为什么子view对于Touch事件处理返回true那么其上层的ViewGroup就无法处理Touch事件了!!!!!!!!!     * 为什么子view对于Touch事件处理返回false那么其上层的ViewGroup才可以处理Touch事件!!!!!!!!!!     */    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) {                //调用自身的dispatchTouchEvent()!!!!!!                    handled = super.dispatchTouchEvent(event);                } else {                    final float offsetX = mScrollX - child.mLeft;                    final float offsetY = mScrollY - child.mTop;                    event.offsetLocation(offsetX, offsetY);                    //调用子View的dispatchTouchEvent()!!!!!!                    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);        }        transformedEvent.recycle();        return handled;    }  //===============以上为dispatchTransformedTouchEvent()源码分析=================}