android-----事件分发机制测试系列
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先来说说我遇到的问题，这次测试使用的布局文件是：
<com.hzw.eventtest.MyRelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<com.hzw.eventtest.MyLinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.hzw.eventtest.MyButton
android:id="@+id/mybutton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="我的按钮" />
</com.hzw.eventtest.MyLinearLayout>
</com.hzw.eventtest.MyRelativeLayout>也就是说布局图是酱紫的：
具体就是我在MyRelativeLayout中拦截了MOVE事件，在MyLinearLayout中拦截并且消费了DOWN事件，也就是说我仅仅修改了MyRelativeLayout$onInterceptTouchEvent中case条件为MOVE的部分以及MyLinearLayout$onInterceptTouchEvent中case条件为DOWN的部分和MyLinearLayout$onTouchEvent中case条件为DOWN的部分；
具体测试代码：点击下载
最后查看Logcat输出：
06-28 09:09:25.237: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_DOWN
06-28 09:09:25.237: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_DOWN
06-28 09:09:25.237: I/System.out(1643): MyRelativeLayout--->onInterceptTouchEvent--->ACTION_DOWN
06-28 09:09:25.237: I/System.out(1643): MyRelativeLayout--->onInterceptTouchEvent--->ACTION_DOWN--->false
06-28 09:09:25.237: I/System.out(1643): MyLinearLayout--->dispatchTouchEvent--->ACTION_DOWN
06-28 09:09:25.237: I/System.out(1643): MyLinearLayout--->onInterceptTouchEvent--->ACTION_DOWN
06-28 09:09:25.237: I/System.out(1643): MyLinearLayout--->onInterceptTouchEvent--->ACTION_DOWN--->true
06-28 09:09:25.246: I/System.out(1643): MyLinearLayout--->onTouchEvent--->ACTION_DOWN
06-28 09:09:25.246: I/System.out(1643): MyLinearLayout--->onTouchEvent--->ACTION_DOWN--->true
06-28 09:09:25.246: I/System.out(1643): MyLinearLayout--->dispatchTouchEvent--->ACTION_DOWN--->true
06-28 09:09:25.246: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_DOWN--->true
06-28 09:09:25.246: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_DOWN--->true
06-28 09:09:25.326: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_MOVE
06-28 09:09:25.326: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_MOVE
06-28 09:09:25.326: I/System.out(1643): MyRelativeLayout--->onInterceptTouchEvent--->ACTION_MOVE
06-28 09:09:25.326: I/System.out(1643): MyRelativeLayout--->onInterceptTouchEvent--->ACTION_MOVE--->true
06-28 09:09:25.326: I/System.out(1643): MyLinearLayout--->dispatchTouchEvent--->ACTION_CANCEL
06-28 09:09:25.326: I/System.out(1643): MyLinearLayout--->dispatchTouchEvent--->ACTION_CANCEL--->false
06-28 09:09:25.326: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_MOVE--->false
06-28 09:09:25.326: I/System.out(1643): MainActivity--->onTouchEvent--->ACTION_MOVE
06-28 09:09:25.326: I/System.out(1643): MainActivity--->onTouchEvent--->ACTION_MOVE--->false
06-28 09:09:25.326: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_MOVE--->false
06-28 09:09:25.336: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_MOVE
06-28 09:09:25.336: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_MOVE
06-28 09:09:25.336: I/System.out(1643): MyRelativeLayout--->onTouchEvent--->ACTION_MOVE
06-28 09:09:25.336: I/System.out(1643): MyRelativeLayout--->onTouchEvent--->ACTION_MOVE--->false
06-28 09:09:25.336: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_MOVE--->false
06-28 09:09:25.336: I/System.out(1643): MainActivity--->onTouchEvent--->ACTION_MOVE
06-28 09:09:25.336: I/System.out(1643): MainActivity--->onTouchEvent--->ACTION_MOVE--->false
06-28 09:09:25.336: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_MOVE--->false
06-28 09:09:25.412: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_UP
06-28 09:09:25.416: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_UP
06-28 09:09:25.416: I/System.out(1643): MyRelativeLayout--->onTouchEvent--->ACTION_UP
06-28 09:09:25.416: I/System.out(1643): MyRelativeLayout--->onTouchEvent--->ACTION_UP--->false
06-28 09:09:25.416: I/System.out(1643): MyRelativeLayout--->dispatchTouchEvent--->ACTION_UP--->false
06-28 09:09:25.416: I/System.out(1643): MainActivity--->onTouchEvent--->ACTION_UP
06-28 09:09:25.416: I/System.out(1643): MainActivity--->onTouchEvent--->ACTION_UP--->false
06-28 09:09:25.416: I/System.out(1643): MainActivity--->dispatchTouchEvent--->ACTION_UP--->false
下面我们来分析下具体的输出过程
为了便于分析，先来贴出此测试过程中用到的部分源码：
ViewGroup$dispatchTouchEvent
@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;
// 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);
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;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
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)) {
continue;
}
newTouchTarget = getTouchTarget(child);
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) {
// 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 (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 (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
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) {
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);
}
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);
}
// Done.
transformedEvent.recycle();
return handled;
}具体分析过程：
注意：分发顺序是：Activity----->ViewGroup----->View
消费顺序是：View------>ViewGroup----->Activity
View中的事件方法执行流程是：dispatchTouchEvent----->onTouchEvent
ViewGroup中的事件方法执行流程是：dispatchTouchEvent----->onInterceptTouchEvent----->onTouchEvent
(1)先来看DOWN事件部分：
事件首先传递到MainActivity，调用它的dispatchTouchEvent分发到他的子View(MyRelativeLayout上)，因为是DOWN事件，满足ViewGroup$dispatchTouchEvent源码的第23行if语句的第一个条件，进入if语句块中，因为我们并没有调用requestDisallowInterceptTouchEvent来干预事件的分发过程，所以会执行第27行的onInterceptTouchEvent方法，我们的测试中MyRelativeLayout没有拦截DOWN事件，因而该方法默认返回值是false赋给intercepted，所以你有了Logcat第4行的输出，接着执行第46行，满足if语句条件，进入if语句块中，这个里面比较关键的代码是第85行的dispatchTransformedTouchEvent方法，这个方法会递归的处理当前View的子View，所以你会发现Logcat第11行MyRelativeLayout的dispatchTouchEvent方法才算真正结束，这里只需要知道第91行会调用addTouchTarget方法，该方法会在其子View的分发事件(dispatchTouchEvent)返回true的情况下执行，在它里面会给mFirstTouchTarget赋值即可，因为MyRelativeLayout子View是MyLinearLayout，所以执行MyLinearLayout的dispatchTouchEvent方法，接着执行MyLinearLayout的onInterceptTouchEvent方法，因为MyLinearLayout拦截了DOWN事件，因而onInterceptTouchEvent返回true，那么这时候ViewGroup$dispatchTouchEvent的第46---108行代码将不再执行，因为此时mFirstTouchTarget还是null的，所以会执行第111行的if语句块，调用dispatchTransformedTouchEvent方法，传入的第三个参数是null，查看ViewGroup$dispatchTransformedTouchEvent源码的第11行，发现他会执行super的dispatchTouchEvent方法，因为我们没有为MyLinearLayout设置onTouch监听事件，所以他直接执行了onTouchEvent方法，并且我们消费了这个DOWN事件，所以有了Logcat第9行的输出，接下来就是递归返回过程了，即Logcat第10--12行的输出部分；
(2)接下来分析第一次MOVE事件
和上面一样，事件首先到了MainActivity，调用他的dispatchTouchEvent方法进行分发，接着事件分发到了MyRelativeLayout上面，调用他的dispatchTouchEvent方法，因为第一次DOWN事件中，我们已经将mFirstTouchTarget的值设置为非null，所以ViewGroup$dispatchTouchEvent方法走到第23行的时候仍然满足if判断条件，执行第27行的onInterceptTouchEvent方法，所以有了第15行的Logcat输出，因为我们在MyRelativeLayout中拦截了MOVE事件，所以intercepted的值将会被赋值为true，因而ViewGroup$dispatchTouchEvent的第46--108行的代码将不会执行，到了第111行判断mFirstTouchTarget不为null，执行else语句部分，这里比较关键的在于第125行，因为此时的intercepted值为true，所以cancelChild值将为true，在执行第127行dispatchTransformedTouchEvent的时候将cancelChild值传入，查看ViewGroup$dispatchTransformedTouchEvent的源码第9行，你会发现他执行了ACTION_CANCEL，所以出现了我们Logcat输出的第17/18行，因而第127行的if条件内容将为false，所以handled的值此时仍然是false，因为cancelChild值是true，所以执行第131行，并且此时的predecessor等于null，因而修改mFirstTouchTarget的值为next，这里就比较重要了，此处的next是null，为什么呢？因为之前mFirstTouchTarget的值是MyLinearLayout，虽然MyLinearLayout有子View(MyButton)，但是MyLinearLayout把DOWN时间消费了，所以MyButton根本就没有加入到事件处理的链表中，所以对mFirstTouchTarget的值进行了修改，ViewGroup$dispatchTouchEvent的第148--161行不再会修改handled的值，那么我们可以认为MyRelativeLayout的dispatchTouchEvent方法执行结束，因为此时事件还没有被消费，那么只能由MainActivity来进行处理了，所以有了Logcat第20--22行的输出；
(3)接下来分析第二次以后的MOVE事件
同样事件首先由MainActivity的dispatchTouchEvent分发到MyRelativeLayout上，执行他的dispatchTouchEvent方法，这时候判断ViewGroup$dispatchTouchEvent第23行的if语句部分，发现部门组条件，那么会执行第35行的else语句部分，设置intercepted的值为true，同样的不会执行第46--108行部分，在判断第111行的mFirstTouchTarget是否为null时，满足条件，执行dispatchTransformedTouchEvent方法，传入的第3个参数是null，那么会执行super的dispatchTouchEvent方法，这属于View的事件分发过程，同样我们没有为MyRelativeLayout设置onTouch方法，所以他会直接执行onTouchEvent方法，所以有了Logcat第25行的输出，接下来在onTouchEvent执行结束之后返回false，因为我们没有在MyRelativeLayout中消费MOVE事件，因为该事件没有处理完，因而会回传给MainActivity来进行处理；
(4)接下来就是UP事件了：
UP事件的分析和第二次以后的MOVE事件过程一致，就不再赘述了；
从上面的分析中，我们可以得出结论：
某一个View一旦决定拦截，那么这个事件序列以后的部分只能由他来处理，前提条件是以后的事件是可以到达该View的，就像上面的例子，DOWN事件是由MyLinearLayout来拦截消费的，但是MOVE事件却不是他处理的，原因在于MyRelativeLayout对MOVE事件进行了拦截，事件根本就不会到达MyLinearLayout；
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