事件分发典型bug：RecycleView滑动嵌套问题解决

更新时间:2023-04-07 12:49:49 阅读：评论：0

简介

现象

在工作中碰到了一个易用性的问题，当一个横向滑动的HorizonRecycleView（注意这里只是一个普通的加了日志打印的RecycleView，并没有改动其自身逻辑），每个Item都包含了一个纵向滑动的VerticalRecycleView（同上）时，若此时想去滑动纵向的VerticalRecycleView，很容易触发到HorizonRecycleView的横向滑动。可能说起来有点绕，直接看图可能更明显点。

代码

代码比较简单，A与B都使用的是LinearLayoutManager，这里展示一下他们item的layout文件

HorizonRecycleView的item

每个item左边是一个TextView，右边是一个VerticalRecycleView

<?xml version="1卓刀泉中学.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="400dp" android:background="@android:color/holo_blue_light" android:layout_marginEnd="20dp" android:layout_height="match_parent">    <TextView android:id="@+id/tv_title_horizon" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toStartOf="@id/rv_vertical" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" />    <com.kyrie.proj.blog.nestedscroll.VerticalRecycleView android:id="@+id/rv_vertical" android:layout_width="200dp" android:layout_height="match_parent" app:layout_constraintEnd_toEndOf="parent" /></androidx.constraintlayout.widget.ConstraintLayout>

VerticalRecycleView的item

只有一个TextView

<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="50dp" android:layout_marginBottom="20dp" android:background="@android:color/holo_green_light">    <TextView android:id="@+id/tv_title_vertical" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" /></androidx.constraintlayout.widget.ConstraintLayout>

问题分析

日志分析

我们把两个RecycleView的dispatchTouchEvent、onInterceptTouchEvent、onTouchEvent都加上打印，来分别比较一下正常滑动VerticalRecycleView和误触发了HorizonRecycleView滑动的日志有什么区别

正常竖直滑动

//ACTION_DONW事件分发I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_DOWNI/wzt: [HorizonRecycleView][onInterceptTouchEvent] e = = ACTION_DOWNI/wzt: [HorizonRecycleView][onInterceptTouchEvent] return fal //HorizonRecycleView不强制拦截I/wzt: [VerticalRecycleView][dispatchTouchEvent] ev = ACTION_DOWNI/wzt: [VerticalRecycleView][onInterceptTouchEvent] e = = ACTION_DOWNI/wzt: [VerticalRecycleView][onInterceptTouchEvent] return fal //VerticalRecycleView不强制拦截I/wzt: [VerticalRecycleView][onTouchEvent] e = = ACTION_DOWNI/wzt: [VerticalRecycleView][onTouchEvent] return true //VerticalRecycleView消费此事件I/wzt: [VerticalRecycleView][dispatchTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] return true//ACTION_DONW事件分发结束，被VerticalRecycleView消费//ACTION_MOVE事件分发I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_MOVEI/wzt: [HorizonRecycleView][onInterceptTouchEvent] e = = ACTION_MOVEI/wzt: [HorizonRecycleView][onInterceptTouchEvent] return falI/wzt:公务员面试真题及答案 [VerticalRecycleView][dispatchTouchEvent] ev = ACTION_MOVEI/wzt: [VerticalRecycleView][onTouchEvent] e = = ACTION_MOVEI/wzt: [VerticalRecycleView][onTouchEvent] return true //VerticalRecycleView消费此ACTION_MOVE事件I/wzt: [VerticalRecycleView][dispatchTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] return true//ACTION_MOVE事件分发结束//ACTION_MOVE事件分发I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_MOVEI/wzt: [HorizonRecycleView][onInterceptTouchEvent] e = = ACTION_MOVE//...//上面省略N个MOVE事件分发//ACTION_UP事件分发I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_UPI/wzt: [VerticalRecycleView][dispatchTouchEvent] ev = ACTION_UPI/wzt: [VerticalRecycleView][onTouchEvent] e = = ACTION_UPI/wzt: [VerticalRecycleView][onTouchEvent] return trueI/wzt: [VerticalRecycleView][dispatchTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] return true//事件分发流程结束

误触发了横向滑动

//ACTION_DONW事件分发I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_DOWNI/wzt: [HorizonRecycleView][onInterceptTouchEvent] e = = ACTION_DOWNI/wzt办公室制度: [HorizonRecycleView][onInterceptTouchEvent] return falI/wzt: [VerticalRecycleView][dispatchTouchEvent] ev = ACTION_DOWNI/wzt: [VerticalRecycleView][onInterceptTouchEvent] e = = ACTION_DOWNI/wzt: [VerticalRecycleView][onInterceptTouchEvent] return falI/wzt: [VerticalRecycleView][onTouchEvent] e = = ACTION_DOWNI/wzt: [VerticalRecycleView][onTouchEvent] return true //VerticalRecycleView消费I/wzt: [VerticalRecycleView][dispatchTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] return true//ACTION_DONW事件分发结束，流程与正常情况完全一致//ACTION_MOVE事件分发I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_MOVEI/wzt: [HorizonRecycleView][onInterceptTouchEvent] e = = ACTION_MOVEI/wzt: [HorizonRecycleView][onInterceptTouchEvent] return falI/wzt: [VerticalRecycleView][dispatchTouchEvent] ev = ACTION_MOVEI/wzt: [VerticalRecycleView][onTouchEvent] e = = ACTION_MOVEI/wzt: [VerticalRecycleView][onTouchEvent] return true //VerticalRecycleView消费//ACTION_MOVE事件分发结束//ACTION_MOVE事件分发//...//上面省略了大概5个MOVE事件分发，都和正常竖直滑动时一致//注1：注意注意注意啦！！！：从这里开始就是重头戏//ACTION_MOVE事件分发I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_MOVEI/wzt: [HorizonRecycleView][onInterceptTouchEvent] e = = ACTION_MOVEI/wzt: [HorizonRecycleView][onInterceptTouchEvent] return true //注2：这里直接被HorizonRecycleView拦截//事件被父控件拦截，导致VerticalRecycleView只能收到一个ACTION_CANCEL事件I/wzt: [VerticalRecycleView][dispatchTouchEvent] ev = ACTION_CANCEL I/wzt: [VerticalRecycleView][onTouchEvent] e = = ACTION_CANCELI/wzt: [VerticalRecycleView][onTouchEvent] return trueI/wzt: [VerticalRecycleView][dispatchTouchEvent] return true //VerticalRecycleView消费了ACTION_CANCEL事件之后，此次滑动序列再也没有收到任何事件I/wzt: [HorizonRecycleView][dispatchTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_MOVE//之后的所有MOVE事件，不会再走onInterceptTouchEvent方法，直接交给HorizonRecycleView消费I/wzt: [HorizonRecycleView][onTouchEvent] e = = ACTION_MOVEI/wzt: [HorizonRecycleView][onTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] return true//ACTION_MOVE事件分发开始I/wzt: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_MOVEI/wzt: [HorizonRecycleView][onTouchEvent] e = = ACTION_MOVEI/wzt: [HorizonRecycleView][onTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] return true//...//省略N个MOVE事件分发//ACTION_UP事件分发，与正常现象一致I/wzt赚钱加盟: [HorizonRecycleView][dispatchTouchEvent] ev = ACTION_UPI/wzt: [HorizonRecycleView][onTouchEvent] e = = ACTION_UPI/wzt: [HorizonRecycleView][onTouchEvent] return trueI/wzt: [HorizonRecycleView][dispatchTouchEvent] return true

日志分析总结

通过如上两个日志对比我们发现，出现问题的原因在于<注2>部分，HorizonRecycleView拦截了一次MOVE事件，导致VerticalRecycleView后续除了一个CANCEL外无法收到任何事件。

ACTION_CANCEL

这里稍微提一下我一直都没有理解的ACTION_CANCEL，从上面的日志我们就可以了解到ACTION_CANCEL出现的场景：当一个View在消费一个事件序列的过程中，父控件拦截了此次事件（父控件onInterceptTouchEvent返回true），这个View就会收到一个ACTION_CANCEL，并且View在此时进行内部状态的重置，如从常态恢复成点击态。并且此次事件序列的后续事件都会直接交给父控件处理。

原因

从日志分析可得横向滑动的误触发是由于HorizonRecycleView的事件拦截引起，那么直接到RecycleView源码里分析一下为何会在MOVE过程中拦截。注意下面的源码省略了非关键的部分

//RecycleView.java@Overridepublic boolean onInterceptTouchEvent(MotionEvent e) {    final int action = e.getActionMasked();    switch (action) {        ca MotionEvent.ACTION_DOWN: {            //在DOWN时记录手指点击的区域            //这里加0.5f的原因是为了转成int值时四舍五入            mInitialTouchX = (int) (e.getX() + 0.5f);            mInitialTouchY = (int) (e.getY() + 0.5f);        }        ca MotionEvent.ACTION_MOVE: {            final int x = (int) (e.getX(index) + 0.5f);            final int y = (int) (e.getY(index) + 0.5f);            //当前不是拖动状态则进行判断            if (mScrollState != SCROLL_STATE_DRAGGING) {                //算出手指移动的距离                final int dx = x - mInitialTouchX;                final int dy = y - mInitialTouchY;                boolean startScroll = fal;                //注1：能横向滚动并且手指移动的距离大于mTouchSlop                //这个mTouchSlop是在RecycleView初始化时确定的滑动临界值，大于这个值就从静止切换为滑动状态                if (canScrollHorizontally && Math.abs(dx) > mTouchSlop) {                    //这里标志位为true                    startScroll = true;                }                //竖直方向，效果同上                if (canScrollVertically && Math.abs(dy) > mTouchSlop) {                    startScroll = true;                }                if (startScroll) {                    //方法内部会把mScrollState置为SCROLL_STATE_DRAGGING                    tScrollState(SCROLL_STATE_DRAGGING);                }            }        }    }    //若为SCROLL_STATE_DRAGGING状态则return true拦截事件    return mScrollState == SCROLL_STATE_DRAGGING;}

从上面的源码<注1>可以看到，在MOVE事件中，若当前手指在HorizonRecycleView横向的滑动大于滑动临界值，则HorizonRecycleView 会直接不去判断其它任何条件置为滑动状态，直接拦截此事件。这就是问题根本原因所在了，HorizonRecycleView只是判断手指在x轴的移动距离超过了临界值就直接强行拦截后续事件。

解决方案

知道了问题原因，解决方案很明显就是如何让HorizonRecycleView不去拦截此次MOVE事件呢。有两种方法

重写HorizonRecycleView的onInterceptTouchEvent方法逻辑，修改判断切换滑动状态的部分通过内部拦截法

方案1：重写HorizonRecycleView的onInterceptTouchEvent逻辑

方案来自于修复RecyclerView嵌套滚动问题，在大佬基础上有少量简化

直接在BetterRecyclerView照着RecycleView源码重写onInterceptTouchEvent，用BetterRecyclerView代替HorizonRecycleView原本的位置即可

//BetterRecyclerView.javapublic class BetterRecyclerView extend沧州的大学s RecyclerView{private static final int INVALID_POINTER = -1;private int mScrollPointerId = INVALID_POINTER;private int mInitialTouchX, mInitialTouchY;private int mTouchSlop;public BetterRecyclerView(Context context) {this(context, null);}public BetterRecyclerView(Context context, @Nullable AttributeSet attrs) {this(context, attrs, 0);}public BetterRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);final ViewConfiguration vc = ViewConfiguration.get(getContext());mTouchSlop = vc.getScaledTouchSlop();}@Overridepublic void tScrollingTouchSlop(int slopConstant) {super.tScrollingTouchSlop(slopConstant);final ViewConfiguration vc = ViewConfiguration.get(getContext());switch (slopConstant) {ca TOUCH_SLOP_DEFAULT:mTouchSlop = vc.getScaledTouchSlop();break;ca TOUCH_SLOP_PAGING:mTouchSlop = vc.getScaledPagingTouchSlop();break;default:break;}}@Overridepublic boolean onInterceptTouchEvent(MotionEvent e) {LayoutManager mLayout = getLayoutManager();if (mLayout == null) {return fal;}final boolean canScrollHorizontally = mLayout.canScrollHorizontally();final boolean canScrollVertically = mLayout.canScrollVertically();final int action = e.getActionMasked();final int actionIndex = e.getActionIndex();switch (action) {ca MotionEvent.ACTION_DOWN:mScrollPointerId = e.getPointerId(0);mInitialTouchX = (int) (e.getX() + 0.5f);mInitialTouchY = (int) (e.getY() + 0.5f);return super.onInterceptTouchEvent(e);ca MotionEvent.ACTION_POINTER_DOWN:mScrollPointerId = e.getPointerId(actionIndex);mInitialTouchX = (int) (e.getX(actionIndex) + 0.5f);mInitialTouchY = (int) (e.getY(actionIndex) + 0.5f);return super.onInterceptTouchEvent(e);ca MotionEvent.ACTION_MOVE: {final int index = e.findPointerIndex(mScrollPointerId);if (index < 0) {return fal;}final int x = (int) (MotionEventCompat.getX(e, index) + 0.5f);final int y = (int) (MotionEventCompat.getY(e, index) + 0.5f);if (getScrollState() != SCROLL_STATE_DRAGGING) {final int dx = x - mInitialTouchX;final int dy = y - mInitialTouchY;boolean startScroll = fal;//注1：注意这里，在原本的基础上加入了dx>dy的判断if (canScrollHorizontally && Math.abs(dx) > mTouchSlop && Math.abs(dx) >= Math.abs(dy)) {startScroll = true;}if (canScrollVertically && Math.abs(dy) > mTouchSlop && Math.abs(dy) >= Math.abs(dx)) {startScroll = true;}return startScroll && super.onInterceptTouchEvent(e);}return super.onInterceptTouchEvent(e);}default:return super.onInterceptTouchEvent(e);}}}

从上面的代码<注1>看到，在原本的基础上加入了dx与dy绝对值比较的判断。只有当手指横向移动的距离大于纵向移动的距离，我们才去走原本的拦截逻辑。

效果

优点

只需重写父控件的onInterceptTouchEvent

缺点

由于重写时简化了RecycleView的onInterceptTouchEvent逻辑，移除了一些其他判断条件，可能存在特殊情况下的隐藏风险（目前暂未发现）

方案2：通过内部拦截法

内部拦截法步骤如下：

外部HorizonRecycleView拦截ACTION_DOWN以外的其它事件（ACTION_DOWN若拦截了会导致子控件无法收到任何焦点）内部VerticalRecycleView在ACTION_DOWN时调用requestDisallowInterceptTouchEvent(true)不允许父控件拦截，即之后MOVE事件都不会走外部HorizonRecycleView的拦截逻辑内部VerticalRecycleView在ACTION_MOVE时判断，若自己不需要滑动，则调用requestDisallowInterceptTouchEvent(fal)重新走父控件HorizonRecycleView的拦截逻辑
代码实现如下

class HorizonRecycleView @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : RecyclerView(context, attrs, defStyleAttr) {override fun onInterceptTouchEvent(e: MotionEvent?): Boolean {//若不调用onInterceptTouchEvent，直接返回true或fal会导致滑动的瞬间瞬移或首次无法横移的问题。var result = super.onInterceptTouchEvent(e)when (e.action) {MotionEvent.ACTION_DOWN ->{result = fal}}return result}}

class VerticalRecycleView @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : RecyclerView(context, attrs, defStyleAttr) {var downX = 0fvar downY = 0foverride fun dispatchTouchEvent(ev: MotionEvent?): Boolean {Log.i("wzt", "[VerticalRecycleView][dispatchTouchEvent] ev = ${MotionEvent.actionToString(ev!!.action)}")when (ev.action) {MotionEvent.ACTION_DOWN -> {downX = ev.xdownY = ev.yLog.i("wzt","[VerticalRecycleView][dispatchTouchEvent]不允许父控件拦截")getParentRecycleView()?.requestDisallowInterceptTouchEvent(true)}MotionEvent.ACTION_MOVE -> {val currentX = ev.xval currentY = ev.yval x = abs(currentX - downX)val y = abs(currentY - downY)if (y < x) {//表示我不需要消费此事件Log.i("wzt","允许拦截")getParentRecycleView()?.requestDisallowInterceptTouchEvent(fal)}}}val result = super.dispatchTouchEvent(ev)Log.i("wzt", "[VerticalRecycleView][dispatchTouchEvent] return $result")return result}/** * 返回父RecycleView，这里直接往上级最高三层查找 */private fun getParentRecycleView() :RecyclerView? {return when {parent is RecyclerView -> parent as RecyclerViewparent.parent is RecyclerView -> parent.parent as RecyclerViewparent.parent.parent is RecyclerView -> parent.parent.parent as RecyclerViewel -> null}}}

使用此方法需要注意：

子控件的判断逻辑需要放在dispatchTouchEvent或onTouchEvent中，因为若自己消费了事件，自身的onInterceptTouchEvent不会再被调用父控件需要调用super.onInterceptTouchEvent(e)，若不调用会导致mInitialTouchX得不到初始化，从而在之后move走到如下流程中无法消费事件，导致无法滑动

@Overridepublic boolean onTouchEvent(MotionEvent e) {ca MotionEvent.ACTION_MOVE: {final int index = e.findPointerIndex(mScrollPointerId);if (index < 0) {Log.e(TAG, "Error processing scroll; pointer index for id "+ mScrollPointerId + " not found. Did any MotionEvents get skipped?");return fal;}}}

效果

优点

逻辑交给子控件自行处理，可操作性更高可以在一个事件序列中先内部竖直滑动，再外部横向滑动

缺点

改动的类更多需要注意的点较多

废弃方案：外部拦截法

通过在MOVE时判断x轴和y轴的移动距离来判断是否需要拦截

@Overridepublic boolean onInterceptTouchEvent(MotionEvent event) {switch (event.getAction()) {ca MotionEvent.ACTION_DOWN:downX = event.getX();downY = event.getY();break;ca MotionEvent.ACTION_MOVE:float currentX = event.getX();float currentY = event.getY();float x = Math.abs(currentX - downX);float y = Math.abs(currentY - downY);return x < y;}return super.onInterceptTouchEvent(event);}

此方案为我最开始使用的方案，但是某个机型的mTouchSlop（滑动临界值）过小，导致若HorizonRecycleView的每个Item除了VerticalRecycleView之外若还有Button之类的控件。很容易触发onInterceptTouchEvent的return ture条件，从而拦截了Item上Button的touch事件，导致Button很难被点击到