Android touch事件处理流程

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final Callback cb = getCallback(); // 和key事件类似，优先派发给Callback，否则直接交给view层次结构处理
return cb != null && !isDestroyed() && mFeatureId < 0 ? cb.dispatchTouchEvent(ev)
: super.dispatchTouchEvent(ev);
}

/**
* Called to process touch screen events. You can override this to
* intercept all touch screen events before they are dispatched to the
* window. Be sure to call this implementation for touch screen events
* that should be handled normally.
*
* @param ev The touch screen event.
*
* @return boolean Return true if this event was consumed.
*/
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction(); // 一开始down事件的时候，调用此callback
}
if (getWindow().superDispatchTouchEvent(ev)) { // 交给了此Activity关联的window处理，实际是派发到view层次结构中
return true; // 如果被window处理掉了（消费了）则返回true，
}
return onTouchEvent(ev); // 否则调用Activity自己的onTouchEvent进行最后的处理
}

@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event); // window直接交给了DecorView处理
} public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event); // DecorView直接交给了其super，即ViewGroup处理
}

/**
* Pass the touch screen motion event down to the target view, or this
* view if it is the target.
*
* @param event The motion event to be dispatched.
* @return True if the event was handled by the view, false otherwise.
*/
public boolean dispatchTouchEvent(MotionEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
} if (onFilterTouchEventForSecurity(event)) { // 一般都成立
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) { // 先在ENABLED状态下尝试调用onTouch方法
return true; // 如果被onTouch处理了，则直接返回true
}
// 从这里我们可以看出，当你既设置了OnTouchListener又设置了OnClickListener，那么当前者返回true的时候，
// onTouchEvent没机会被调用，当然你的OnClickListener也就不会被触发；另外还有个区别就是onTouch里可以
// 收到每次touch事件，而onClickListener只是在up事件到来时触发。
if (onTouchEvent(event)) {
return true;
}
} if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
return false; // 上面的都没处理，则返回false
} /**
* Implement this method to handle touch screen motion events.
* <p>
* If this method is used to detect click actions, it is recommended that
* the actions be performed by implementing and calling
* {@link #performClick()}. This will ensure consistent system behavior,
* including:
* <ul>
* <li>obeying click sound preferences
* <li>dispatching OnClickListener calls
* <li>handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
* accessibility features are enabled
* </ul>
*
* @param event The motion event.
* @return True if the event was handled, false otherwise.
*/
public boolean onTouchEvent(MotionEvent event) { // View对touch事件的默认处理逻辑
final int viewFlags = mViewFlags; if ((viewFlags & ENABLED_MASK) == DISABLED) { // DISABLED的状态下
if (event.getAction() == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false); // 复原，如果之前是PRESSED状态
}
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return (((viewFlags & CLICKABLE) == CLICKABLE || // CLICKABLE或LONG_CLICKABLE的view标记为对事件处理了，
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)); // 只不过是以do nothing的方式处理了。
} if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) { // 如果有TouchDelegate的话，优先交给它处理
return true; // 处理了返回true，否则接着往下走
}
} if (((viewFlags & CLICKABLE) == CLICKABLE || // View能对touch事件响应的前提要么是CLICKABLE要么是LONG_CLICKABLE
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
switch (event.getAction()) {
case MotionEvent.ACTION_UP: // UP事件
// 如果外围有可以滚动的parent的话，当按下时会设置这个标志位
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) { // 按下了或者预按下了
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
// 这行代码就是我们上篇博客中说的，设置了FocusableInTouchMode后，View在点击的时候就会
// 尝试requestFocus()，并将focusToken设置为true
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus(); // 能进来这个if，一般都会返回true
} 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.
// 在前面down事件的时候我们延迟显示view的pressed状态
setPressed(true); // 直到up事件到来的时候才显示pressed状态
} if (!mHasPerformedLongPress) { // 如果没有长按发生的话
// This is a tap, so remove the longpress check
removeLongPressCallback(); // 移除长按callback // Only perform take click actions if we were in the pressed state
if (!focusTaken) { // 看到没，focusTaken是false才会进入下面的if语句
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
// 也就是说在touch mode下，不take focus的view第一次点击的时候才会触发onClick事件
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) { // 如果post失败了，则直接调用performClick()方法
performClick(); // 这2行代码会触发onClickListener
}
}
} if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState(); // unset按下状态的
} if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
break; case MotionEvent.ACTION_DOWN: // DOWN事件
mHasPerformedLongPress = false; if (performButtonActionOnTouchDown(event)) {
break;
} // Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer(); // For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) { // 如果是在可以滚动的container里面的话
mPrivateFlags |= PFLAG_PREPRESSED; // 设置PREPRESSED标志位
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
} // 延迟pressed feedback
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true); // 否则直接显示pressed feedback
checkForLongClick(0); // 并启动长按监测
}
break; case MotionEvent.ACTION_CANCEL: // 针对CANCEL事件的话，恢复各种状态，移除各种callback
setPressed(false);
removeTapCallback();
removeLongPressCallback();
break; case MotionEvent.ACTION_MOVE: // MOVE事件
final int x = (int) event.getX();
final int y = (int) event.getY(); // Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) { // 如果移动到view的边界之外了，
// Outside button
removeTapCallback(); // 则取消Tap callback，这样当你松手的时候onClick不会被触发
if ((mPrivateFlags & PFLAG_PRESSED) != 0) { // 当已经是按下状态的话
// Remove any future long press/tap checks
removeLongPressCallback(); // 移除长按callback setPressed(false); // 恢复按下状态
}
}
break;
}
return true; // 最后返回true，表示对touch事件处理过了，消费了
} return false; // 既不能单击也不能长按的View，返回false，表示不处理touch事件
}

/* Describes a touched view and the ids of the pointers that it has captured.
*
* This code assumes that pointer ids are always in the range 0..31 such that
* it can use a bitfield to track which pointer ids are present.
* As it happens, the lower layers of the input dispatch pipeline also use the
* same trick so the assumption should be safe here...
*/
private static final class TouchTarget {
private static final int MAX_RECYCLED = 32;
private static final Object sRecycleLock = new Object[0];
private static TouchTarget sRecycleBin; // 回收再利用的链表头
private static int sRecycledCount; public static final int ALL_POINTER_IDS = -1; // all ones // The touched child view.
public View child; // The combined bit mask of pointer ids for all pointers captured by the target.
public int pointerIdBits; // The next target in the target list.
public TouchTarget next; private TouchTarget() {
}

// 看到这个有没有很眼熟？是的Message里也有类似的实现，我们在之前介绍Message的文章里详细地分析过
public static TouchTarget obtain(View child, int pointerIdBits) {
final TouchTarget target;
synchronized (sRecycleLock) {
if (sRecycleBin == null) { // 没有可以回收的目标，则new一个返回
target = new TouchTarget();
} else {
target = sRecycleBin; // 重用当前的sRecycleBin
sRecycleBin = target.next; // 更新sRecycleBin指向下一个
sRecycledCount--; // 重用了一个，可回收的减1
target.next = null; // 切断next指向
}
}
target.child = child; // 找到合适的target后，赋值
target.pointerIdBits = pointerIdBits;
return target;
} public void recycle() { // 基本是obtain的反向过程
synchronized (sRecycleLock) {
if (sRecycledCount < MAX_RECYCLED) {
next = sRecycleBin; // next指向旧的可回收的头
sRecycleBin = this; // update旧的头指向this，表示它自己现在是可回收的target（第一个）
sRecycledCount += 1; // 多了一个可回收的
} else {
next = null; // 没有next了
}
child = null; // 清空child字段
}
}
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
} boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) { // view没有被遮罩，一般都成立
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK; // Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) { // 一堆touch事件（从按下到松手）中的第一个down事件
// 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(); // 作为新一轮的开始，reset所有相关的状态
} // Check for interception.
final boolean intercepted; // 检查是否要拦截
if (actionMasked == MotionEvent.ACTION_DOWN // down事件
|| mFirstTouchTarget != null) { // 或者之前的某次事件已经经由此ViewGroup派发给children后被处理掉了
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) { // 只有允许拦截才执行onInterceptTouchEvent方法
intercepted = onInterceptTouchEvent(ev); // 默认返回false，不拦截
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false; // 不允许拦截的话，直接设为false
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
// 在这种情况下，actionMasked != ACTION_DOWN && mFirstTouchTarget == null
// 第一次的down事件没有被此ViewGroup的children处理掉（要么是它们自己不处理，要么是ViewGroup从一
// 开始的down事件就开始拦截），则接下来的所有事件
// 也没它们的份，即不处理down事件的话，那表示你对后面接下来的事件也不感兴趣
intercepted = true; // 这种情况下设置ViewGroup拦截接下来的事件
} // Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL; // 此touch事件是否取消了 // Update list of touch targets for pointer down, if needed.
// 是否拆分事件，3.0(包括)之后引入的，默认拆分
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null; // 接下来ViewGroup判断要将此touch事件交给谁处理
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) { // 没取消也不拦截，即是个有效的touch事件
if (actionMasked == MotionEvent.ACTION_DOWN // 第一个手指down
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) // 接下来的手指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 (newTouchTarget == null && childrenCount != 0) { // 基本都成立
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();
// 从最后一个向第一个找
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; // 不满足这2个条件直接跳过，看下一个child
} // child view能receive touch事件而且touch坐标也在view边界内 newTouchTarget = getTouchTarget(child);// 查找child对应的TouchTarget
if (newTouchTarget != null) { // 比如在同一个child上按下了多跟手指
// 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; // newTouchTarget已经有了，跳出for循环
} resetCancelNextUpFlag(child);
// 将此事件交给child处理
// 有这种情况，一个手指按在了child1上，另一个手指按在了child2上，以此类推
// 这样TouchTarget的链就形成了
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();
// 如果处理掉了的话，将此child添加到touch链的头部
// 注意这个方法内部会更新 mFirstTouchTarget
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true; // down或pointer_down事件已经被处理了
break; // 可以退出for循环了。。。
}
}
} // 本次没找到newTouchTarget但之前的mFirstTouchTarget已经有了
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;
}
// while结束后，newTouchTarget指向了最初的TouchTarget
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// 非down事件直接从这里开始处理，不会走上面的一大堆寻找TouchTarget的逻辑
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// 没有children处理则派发给自己处理
// 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) { // 遍历TouchTarget形成的链表
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true; // 已经处理过的不再让其处理事件
} else {
// 取消child标记
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
// 如果ViewGroup从半路拦截了touch事件则给touch链上的child发送cancel事件
// 如果cancelChild为true的话
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true; // TouchTarget链中任意一个处理了则设置handled为true
}
if (cancelChild) { // 如果是cancelChild的话，则回收此target节点
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next; // 相当于从链表中删除一个节点
}
target.recycle(); // 回收它
target = next;
continue;
}
}
predecessor = target; // 访问下一个节点
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) {
// 取消或up事件时resetTouchState
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
// 当某个手指抬起时，将其相关的信息移除
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
} if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled; // 返回处理的结果
}

/**
* Implement this method to intercept all touch screen motion events. This
* allows you to watch events as they are dispatched to your children, and
* take ownership of the current gesture at any point.
*
* <p>Using this function takes some care, as it has a fairly complicated
* interaction with {@link View#onTouchEvent(MotionEvent)
* View.onTouchEvent(MotionEvent)}, and using it requires implementing
* that method as well as this one in the correct way. Events will be
* received in the following order:
*
* <ol>
* <li> You will receive the down event here.
* <li> The down event will be handled either by a child of this view
* group, or given to your own onTouchEvent() method to handle; this means
* you should implement onTouchEvent() to return true, so you will
* continue to see the rest of the gesture (instead of looking for
* a parent view to handle it). Also, by returning true from
* onTouchEvent(), you will not receive any following
* events in onInterceptTouchEvent() and all touch processing must
* happen in onTouchEvent() like normal.
* <li> For as long as you return false from this function, each following
* event (up to and including the final up) will be delivered first here
* and then to the target's onTouchEvent().
* <li> If you return true from here, you will not receive any
* following events: the target view will receive the same event but
* with the action {@link MotionEvent#ACTION_CANCEL}, and all further
* events will be delivered to your onTouchEvent() method and no longer
* appear here.
* </ol>
*
* @param ev The motion event being dispatched down the hierarchy.
* @return Return true to steal motion events from the children and have
* them dispatched to this ViewGroup through onTouchEvent().
* The current target will receive an ACTION_CANCEL event, and no further
* messages will be delivered here.
*/
public boolean onInterceptTouchEvent(MotionEvent ev) {
return false; // 其默认直接返回false，表示不拦截
}

/**
* Resets all touch state in preparation for a new cycle.
*/
private void resetTouchState() {
clearTouchTargets();
resetCancelNextUpFlag(this);
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
} /**
* Resets the cancel next up flag.
* Returns true if the flag was previously set.
*/
private static boolean resetCancelNextUpFlag(View view) {
if ((view.mPrivateFlags & PFLAG_CANCEL_NEXT_UP_EVENT) != 0) {
view.mPrivateFlags &= ~PFLAG_CANCEL_NEXT_UP_EVENT;
return true;
}
return false;
} /**
* Clears all touch targets.
*/
private void clearTouchTargets() {
TouchTarget target = mFirstTouchTarget;
if (target != null) {
do {
TouchTarget next = target.next;
target.recycle();
target = next;
} while (target != null);
mFirstTouchTarget = null;
}
} /**
* Cancels and clears all touch targets.
*/
private void cancelAndClearTouchTargets(MotionEvent event) {
if (mFirstTouchTarget != null) {
boolean syntheticEvent = false;
if (event == null) {
final long now = SystemClock.uptimeMillis();
event = MotionEvent.obtain(now, now,
MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
syntheticEvent = true;
} for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
resetCancelNextUpFlag(target.child);
dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);
}
clearTouchTargets(); if (syntheticEvent) {
event.recycle();
}
}
} /**
* Gets the touch target for specified child view.
* Returns null if not found.
*/
private TouchTarget getTouchTarget(View child) {
for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
if (target.child == child) {
return target;
}
}
return null;
} /**
* Adds a touch target for specified child to the beginning of the list.
* Assumes the target child is not already present.
*/
private TouchTarget addTouchTarget(View child, int pointerIdBits) {
TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
} /**
* Removes the pointer ids from consideration.
*/
private void removePointersFromTouchTargets(int pointerIdBits) {
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if ((target.pointerIdBits & pointerIdBits) != 0) {
target.pointerIdBits &= ~pointerIdBits;
if (target.pointerIdBits == 0) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
} // 类似从链表中删除某个特定的节点
private void cancelTouchTarget(View view) {
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (target.child == view) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle(); final long now = SystemClock.uptimeMillis();
MotionEvent event = MotionEvent.obtain(now, now,
MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
view.dispatchTouchEvent(event);
event.recycle();
return;
}
predecessor = target;
target = next;
}
}

/**
* Called when a touch screen event was not handled by any of the views
* under it. This is most useful to process touch events that happen
* outside of your window bounds, where there is no view to receive it.
*
* @param event The touch screen event being processed.
*
* @return Return true if you have consumed the event, false if you haven't.
* The default implementation always returns false.
*/
public boolean onTouchEvent(MotionEvent event) { // 没啥需要多说的，好好看方法doc吧
if (mWindow.shouldCloseOnTouch(this, event)) {
finish();
return true;
} return false;
}