Android 事件分发—滑动冲突解决
0.背景知识补充
在Android的触摸消息中，已经实现了三种监测，它们分别是
- pre-pressed：对应的语义是用户轻触(tap)了屏幕
- pressed：对应的语义是用户点击(press)了屏幕
- long pressed：对应的语义是用户长按(long press)了屏幕
下图是触摸消息随时间变化的时间轴示意图：
其中，t0和t1定义在ViewConfiguration类中，标识了tap和longpress的超时时间，定义如下：
/**
* Defines the duration in milliseconds we will wait to see if a touch event
* is a tap or a scroll. If the user does not move within this interval, it is
* considered to be a tap.
*/
private static final int TAP_TIMEOUT = 115; // t0
/**
* Defines the duration in milliseconds before a press turns into
* a long press
*/
private static final int LONG_PRESS_TIMEOUT = 500; // t1
1.梗概
上一节我们详细介绍了，ACTION_DOWN的分发流程，本节来简单讲解下ACTION_MOVE与ACTION_UP的一个大致流程分析，因为这两者的代码流程基本一致，所以一并进行一个讲解
3.view和viewGroup源码详解
开始之前，我们再用上一节的一个流程图来简单回顾一下ACTION_DOWN的流程
而ACTION_UP和ACTION_DOWN不同的一点就在于，当图中最后的VIEW在接收到ACTION_DOWN的通知，对该触控事件不感兴趣时；则之后的ACTION就不再向下分发！
view源码讲解
在view的源代码中，dispatchTouchEvent()方法部分ACTION_UP和ACTION_DOWN部分执行的主流程部分并没有什么区别，主要区别在于 view.onTouchEvent部分，需要进行一定讲解
view.onTouchEvent(event)分析
onTouchEvent就已经可以看到我们最常用的部分代码内容
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();//1.记录坐标点
final int viewFlags = mViewFlags;
final int action = event.getAction();//2.获取action
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE //判断是否开启可以点击的开关
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)//判断长按开关
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;//判断是否可以开启上下文的点击，比如 鼠标右键点击
//部分源代码忽略
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {//a.可以点击的情况情况；b.有悬停和长按显示工具提示框
switch (action) {
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();//暂时忽略
}
if (!clickable) {//不可以点击时，然后跳出switch
removeTapCallback(); //移除 tap（敲打屏幕）的响应
removeLongPressCallback();//移除长按的响应
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
//获取prepressed状态
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
//如果是pressed状态或者是prepressed状态，才进行处理
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {//可获取焦点，可获取焦点的触控模式，且没有获取焦点的情况下，获取到焦点
focusTaken = requestFocus();
}
if (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);//显示按住的状态
}
// 是否处理过长按操作了，如果是，则直接返回
// 进入该代码段，说明这是一个tap操作，首先移除长按回调操作
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
//只有显示了 pressed状态，才执行点击事件
if (!focusTaken) {
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {//点击事件runable放到消息队列里执行
performClickInternal();//放入消息队列失败，手动执行
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
//如果是Tap操作
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
//移除tap回调
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_CANCEL:
//非探讨重点，暂时忽略
case MotionEvent.ACTION_MOVE:
//非探讨重点，暂时忽略
if (clickable) {
drawableHotspotChanged(x, y);
}
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
// Remove any future long press/tap checks
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
break;
case MotionEvent.ACTION_DOWN:
//忽略
}
return true;
}
return false;
}
PerformClick
执行click的用于消息队列的runnalbe
private final class PerformClick implements Runnable {
@Override
public void run() {
performClickInternal();
}
}
performClickInternal
private boolean performClickInternal() {
//点击事件通知自动填充manager
notifyAutofillManagerOnClick();
//执行真实点击事件
return performClick();
}
performClick
public boolean performClick() {
//当点击通知自动填充manager
notifyAutofillManagerOnClick();
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);//响应点击事件
result = true;
} else {
result = false;
}
//通知辅助功能
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
notifyEnterOrExitForAutoFillIfNeeded(true);
return result;
}
viewGroup的分发方法讲解
viewGroup dispatchTouchEvent简析
public boolean dispatchTouchEvent(MotionEvent ev) {
//部分忽略
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {//过滤非正常情况，上文有讲解
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
//部分源代码忽略
final boolean intercepted;//用于viewGroup的拦截 分发的请求直接可以截断不向下下发，而是直接在本层进行处理
if (actionMasked == MotionEvent.ACTION_DOWN //2.一般情况下，为初始 down和down后面mFirstTouchTarget不为空都会触发的
|| mFirstTouchTarget != null) {//b.action为 move or up且有子view时会进入，因为 mFirstTouchTarget不为空
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);//执行拦截回调
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {//什么情况下 no touch targets 且不是初始第一次按下？
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
//部分源代码忽略
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// 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;
/*
intercepted = true时，
if (mFirstTouchTarget == null) {//此对象为空
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);//调用本viewGroup的super的view的方法，即将结果handled进行了赋值，
在后面的 move和up事件过来时，直接当作普通view调用
intercepted = false时，
action down move up都会进入该判断
}
*/
//部分忽略
// 1.d. 有child的情况，都不会进入
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {//当 action 为down dispatchTransformedTouchEvent分发的结果为 false ，开始当作普通view执行
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
//当ACTION_UP或ACTION_MOVE,mFirstTouchTarget已经被赋值过了，即不为空
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
//e. 当 action move up alreadyDispatchedToNewTouchTarget = false 不执行
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
//当action 为 down 事件分发给child，则 alreadyDispatchedToNewTouchTarget = true
//此时 target == newTouchTarget 是成立的 就在 down中调用 addTouchTarget（）使得成立的
handled = true;//有子view的已经处理完毕
} else {//f. 当 action move up
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//通过循环，直接将 down找到的touchTarget对象中保存的view,一一分发对应的move和up事件
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {//为true时就直接将链表向前移动，进行回收掉
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState(); //将FristTouchTarget置空
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
//部分忽略
return handled;//返回结果
}
简单概括
在我们很多针对的事件分发的讨论中，其实主要是针对ACTION_DOWN的一个流向的一个分析，但是根据实际分析可以发现，在ACTION_UP和ACTION_MOVE的情况下，代码执行的流程不同的： 不同主要体现在两个点：
a. View部分:
- view的onTouEvent()部分,针对不同ACTION做的不同处理
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
case MotionEvent.ACTION_UP:
break;
}
b. ViewGroup部分：
- 在dispatchTouchEvent 当中对ACTION_UP做的处理主要就是，排除被拦截的情况外；主要就是直接将 mFirstTouchTarget 中的对应接收事件的child去直接取出来，将事件分发给对应的view
总结
本文目前主要针对的Action_UP的情况的一个重点分析，接下来会补充已下内容：
- 多指触控的事件分发指派
- 对事件感兴趣和不感兴趣的流程图展示
