onInterceptTouchEvent 与 onTouchEvent 分析与MotionEvent在ViewGroup与View中的分发
Notice：本文将紧接着
Android 触屏事件
OnTouch onClick onTouchEvent对于触屏事件的处理和分发
这一片博文来分析，假设您还没有读过这一片博文，强烈建议你先读一次上述博文
OK，言归正传，我们開始吧
近期，一直听到有人在争论关于dispatchTouchEvent这个函数 和 onInterceptTouchEvent这两个函数究竟是那一这真正的决定了MotionEvent的分发。
这里我还是统一给出答案吧。我们都知道假设我们不希望我们的ViewGroup阻拦我们的View获得MotionEvent。我们一般仅仅须要在onInterceptTouchEvent这个函数中return
false（而且该函数默认return false）。或者，在特定的情况下，假设我们希望某些时候交给我们的我们ViewGroup来处理有些情况下我们又希望我们的View来处理MotionEvent。这样的情况下，我们应该怎么来处理呢。我想大家都知道，我们须要在onInterceptTouchEvent做一些处理，由于大家都知道onInterceptTouchEvent是用来做MotionEvent事件的处理对象推断的。
那么，答案非常明显了，处理MotionEvent仅仅有dispatchTouchEvent（事实上这一点从函数名称都能够看出来。更不要说onInterceptTouchEvent还仅仅是ViewGroup特有的方法）。
好，我们先来整理我们眼下已知的。而且提出疑问然后再開始分析
一、Android 中的MotionEvent事件分发处理是由dispatchTouchEvent来完毕的（底层直接调用该方法。我们这里不分析）
二、通过上一篇博文我们知道dispatchTouchEvent > onTouch > onTouchEvent > onClick
这里我还是简单啰嗦一下吧。事实上onTouchListener 和 onClickListener 仅仅是为了提供给上层便捷的处理接口，他们的存在仅仅是为了对于开发提供了便捷，可是在Android中我们通常採用onInterceptTouchEvent和onTouchEvent
联合来推断MotionEvent的处理对象
三、我们在ViewGroup中採用onInterceptTouchEvent和onTouchEvent
联合来推断MotionEvent的处理对象
OK。结论到此结束，我们应该提出问题。
一、既然MotionEvent事件是由dispatchTouchEvent来分发的。那么他和onInterceptTouchEvent又是什么关系呢
二、onInterceptTouchEvent和onTouchEvent
是如何来完毕事件分发的
那么，到了如今，我们的主题仅仅有一个。解决上面的两个问题就可以。
对于第一个问题，最好的解决方案，非常明显我们须要靠源代码来解决
以下，我先给出ViewGroup重写之后的dispatchTouchEvent函数。这里我们须要注意的事他并没有调用super.dispatchTouchEvent。
而是实实在在的重写了全部逻辑（至于View源代码的dispatchTouchEvent，各位看官去我的上一篇博文里面去看看吧）
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
if (DBG_MOTION || DBG_TOUCH) {
Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent 1: ev = " + ev + ",mFirstTouchTarget = "
+ mFirstTouchTarget + ",this = " + this);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) { //上一篇博文中提到的遮蔽推断事实上是错误的，这里指的应该是窗体被其它窗体遮挡。非常明显普通情况下是不会的
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
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();
}
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);//这里開始推断
/// M : add log to help debugging
if (intercepted == true) {
if (DBG_TOUCH) {
Xlog.d(TAG, "Touch event was intercepted event = " + ev + ",this = " + this);
}
}
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.
intercepted = true;
}
// 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;
if (DBG_MOTION) {
Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent 2: actionMasked = " + actionMasked
+ ",intercepted = " + intercepted + ",canceled = " + canceled + ",split = "
+ split + ",mChildrenCount = " + mChildrenCount + ",mFirstTouchTarget = "
+ mFirstTouchTarget + ",this = " + this);
}
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) { //根据interceptd 分析转折点
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 (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.
final View[] children = mChildren;
final boolean customOrder = isChildrenDrawingOrderEnabled();
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)) {
if (DBG_MOTION) {
Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent continue 6: i = "
+ i + ",count = " + childrenCount + ",child = " + child
+ ",this = " + this);
}
continue;
}
newTouchTarget = getTouchTarget(child);
if (DBG_MOTION) {
Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent to child 3: child = "
+ child + ",childrenCount = " + childrenCount + ",i = " + i
+ ",newTouchTarget = " + newTouchTarget + ",idBitsToAssign = "
+ idBitsToAssign + ",mFirstTouchTarget = " + mFirstTouchTarget
+ ",this = " + this);
}
if (newTouchTarget != null) {
// 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);
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();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}
}
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.
if (mFirstTouchTarget == null) {
if (DBG_MOTION) {
Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent mFirstTouchTarget = null, canceled = "
+ canceled + ",this = " + this);
}
// 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) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild, //----------
target.child, target.pointerIdBits)) {
handled = true;
}
if (DBG_MOTION) {
Xlog.d(TAG, "dispatchTouchEvent middle 5: cancelChild = " + cancelChild
+ ",mFirstTouchTarget = " + mFirstTouchTarget + ",target = "
+ target + ",predecessor = " + predecessor + ",next = " + next
+ ",this = " + this);
}
if (cancelChild) {
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();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (DBG_MOTION) {
Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent end 4: handled = " + handled + ",mFirstTouchTarget = "
+ mFirstTouchTarget + ",this = " + this);
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
通过上面我标红色的代码(做标记地方。显示有问题)。我们非常明显的看得出来通过onInterceptTouchEvent终于交给了dispatchTransformedTouchEvent来处理。那么dispatchTransformedTouchEvent又做了什么呢
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 (DBG_MOTION) {
Xlog.d(TAG, "dispatchTransformedTouchEvent 1: event = " + event + ",cancel = "
+ cancel + ",oldAction = " + oldAction + ",desiredPointerIdBits = "
+ desiredPointerIdBits + ",mFirstTouchTarget = " + mFirstTouchTarget
+ ",child = " + child + ",this = " + this);
}
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);
if (DBG_MOTION) {
Xlog.d(TAG, "Dispatch cancel action end: handled = " + handled + ",oldAction = "
+ oldAction + ",child = " + child + ",this = " + this);
}
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) {
Xlog.i(TAG, "Dispatch transformed touch event without pointers in " + this);
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);
}
if (DBG_MOTION) {
Xlog.d(TAG, "dispatchTransformedTouchEvent 2 to child " + child
+ ",handled = " + handled + ",mScrollX = " + mScrollX + ",mScrollY = "
+ mScrollY + ",mFirstTouchTarget = " + mFirstTouchTarget + ",event = "
+ event + ",this = " + this);
}
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);
}
if (DBG_MOTION) {
Xlog.d(TAG, "dispatchTransformedTouchEvent 3 to child " + child + ",handled = "
+ handled + ",mScrollX = " + mScrollX + ",mScrollY = " + mScrollY
+ ",mFirstTouchTarget = " + mFirstTouchTarget + ",transformedEvent = "
+ transformedEvent + ",this = " + this);
}
// Done.
transformedEvent.recycle();
return handled;
}
从上面的代码来推断我们如果我们不重载
public boolean onInterceptTouchEvent(MotionEvent ev) {
return false;
}
那么非常明显了，我们的ViewGroup不会吃掉本次MotionEvent
从上一博文中的MyImageView被点击来推断
当我们点击我们ImageView时
我们继续接着我们的Log来分析
MotionEvent事件首先传递给了我们的MyFrameLayout，这时，我们要注意尽管我们设置了onTouchListener和OnClickListener。可是由于我们没有重载onInterceptTouchEvent默认的onInterceptTouchEvent直接return
false;所以我们的MyFrameLayout没有资格消费本次的MotionEvent事件。终于经过推断dispatchTransformedTouchEvent把事件交给了我们的MyImageView
handled = child.dispatchTouchEvent(transformedEvent);
当然
由于我们的MyImageView 也设置了onTouchListener和onClickListener，所以他顺理成章的消费了本次MotionEvent
当我们再点击我们FrameLayout
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这时尽管我们的onInterceptTouchEvent还是return false；可是我们的touchTarget是空的，所以
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else
我们的MyFrameLayout 也还是终于享受到了MotionEvent
所以说 不一定我们的onInterceptTouchEvent
返回了false 我们的ViewGroup就不能接收到OnTouchEvent了
这里，我们再次考虑
当我们的onInterceptTouchEvent 被我们重载 并返回了true 那么走的路线就不一样了
if (!canceled && !intercepted) { //根据interceptd 分析转折点</span>
if (mFirstTouchTarget == null) {
if (DBG_MOTION) {
Xlog.d(TAG, "(ViewGroup)dispatchTouchEvent mFirstTouchTarget = null, canceled = "
+ canceled + ",this = " + this);
}
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
这里注意，由于我们的onInterceptTouchEvent return true;我们直接跳过了Child的推断并终于导致我们的child == null;那么非常明星我们的MotionEvent仅仅能被我们的ViewGroup消费了。
那么，到了这里我们開始大胆的做出如果性结论：
一、仅仅要我们的onInterceptTouchEvent return
true 那么我们的MotionEvent 与ChildView 无缘
二、假设我们的onInterceptTouchEvent return false。那么我们的ChildView 会优先获得MotionEvent
。可是当我们的ChildView 并不在TouchTarget上，我们的ViewGroup依旧有机会得到本次MotionEvent 。
那么接下来，我们全部做的就仅仅能验证我们的结论了。
这里我们先验证第一条// 这里的验证我们将根据ACTION的不同来分析。
这里我们对我们的MyFrameLayout 做出改变（重载onInterceptTouchEvent ）
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:{
Log.d(TAG,"MyFrameLayout onInterceptTouchEvent ACTION_DOWN return true");
return true;
}
case MotionEvent.ACTION_MOVE:{
Log.d(TAG,"MyFrameLayout onInterceptTouchEvent ACTION_MOVE return true");
return true;
}
case MotionEvent.ACTION_UP:{
Log.d(TAG,"MyFrameLayout onInterceptTouchEvent ACTION_UP return true");
return true;
}
}
return true;
}
简而言之。就是任何情况下，我们都要我们的onInterceptTouchEvent return true；
并分别改写我们的FrameLayout
和ImageView的OnTouchEvent函数
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(TAG,"MyFrameLayout onTouchEvent"+event.getAction());
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:{
Log.d(TAG,"MyFrameLayout onTouchEvent ACTION_DOWN return true");
break;
}
case MotionEvent.ACTION_MOVE:{
Log.d(TAG,"MyFrameLayout onTouchEvent ACTION_MOVE return true");
break;
}
case MotionEvent.ACTION_UP:{
Log.d(TAG,"MyFrameLayout onTouchEvent ACTION_UP return true");
break;
}
}
return super.onTouchEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.d(TAG,"MyImageView onTouchEvent"+event.getAction());
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:{
Log.d(TAG,"MyImageView onTouchEvent ACTION_DOWN return true");
break;
}
case MotionEvent.ACTION_MOVE:{
Log.d(TAG,"MyImageView onTouchEvent ACTION_MOVE return true");
break;
}
case MotionEvent.ACTION_UP:{
Log.d(TAG,"MyImageView onTouchEvent ACTION_UP return true");
break;
}
}
return super.onTouchEvent(event);
}
首先我们点击我们的MyImageView,我们来看一下Log
非常明显。一旦我们的onInterceptTouchEvent
return true,我们的子View就与MotionEvent 无缘了
接下来。我们继续点击我们的FrameLayout
Log 图，我就不贴了，和上面一模一样，为什么呢，非常显然我们的子View就与MotionEvent 无缘了
接下来。我们继续做出改变
我们在FrameLayout中将onInterceptTouchEvent
中的MotionEvent.ACTION_DOWN returnfalse。
依旧点击我们的点击我们的MyImageView
这里我们来分析一下Log 首先我们须要知道3 == MotionEvent.ACTION_CANCEL
那么，首先由于我们的onInterceptTouchEvent 在MotionEvent.ACTION_DOWN
returnfalse；所以我们的FrameLayout没办法继续往下走了（不会走onTouch 和 onTouchEvent）转而MotionEvent事件转交给我们的ImageView
所以我们的ImageView总算是得到了MotionEvent.ACTION_DOWN
可是在经过MotionEvent.ACTION_MOVE时。由于我们的onInterceptTouchEvent
返回了true。所以非常明显我们的FrameLayout告诉了系统 这次的MotionEvent事件我要了。所以我们的ImageView的到了MotionEvent.ACTION_CANCEL
反而我们的FrameLayout 能够继续往下走了。
所以说我们的ImageView猜中了开头缺有猜中结局。尽管得到了ACTION_DOWN，但却什么都做不了仅仅能以ACTION_CANCEL草草收场，所以也不会触发onClickListener
同理我们的FrameLayout尽管得到了ACTION_UP
可是没有ACTION_DOWN 也是徒劳。
相同不会OnClickListener
到了这里，我们相同也是能够类推的
假设我们的FrameLayout在onInterceptTouchEvent 在ACTION_MOVE中返回false，我们的ImageView能够接受到ACTION_MOVE
可是终于接受的还是ACTION_CANCEL依旧接受不到ACTION_UP ，反而我们的FrameLayout
仅仅能得到ACTION_UP 。简而言之就是说根据onInterceptTouchEvent 的返回值不同各MotionEvent事件终于要么被ViewGroup
要么被ChildView获取
从上面的Log，我们依旧能够看到的是 onInterceptTouchEvent
并不会在每一次 MotionEvent事件（ACTION_DOWN、ACTION_MOVE、ACTION_UP
等）调用，例假设在ACTION_DOWN return true 交给了ViewGroup 而View没有得到的话。ACTION_MOVE时就不会调用，可是假设return
false，ChildView 得到了ACTION_MOVE时就会再次调用
