本文是学习Android事件分发机制的学习笔记，一是为了巩固学习成果，加深印象；二是为了方便以后查阅。
Activity对事件的分发过程
从Activity#dispatchTouchEvent()开始看起:
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
首先对ACTION_DOWN 事件进行了特殊判断，调用onUserInteraction() ,跟进这个方法，会发现是一个空方法：
public void onUserInteraction() {
}
不去管它，接下来Activity会通过getWindow() 获得自己所属的Window 进行分发，Window 是个抽象类，用来控制顶级View的外观和行为策略，它的唯一实现类是PhoneWindow 。那么PhoneWindow 是如何处理点击事件的，PhoneWindow#superDispatchTouchEvent() 如下所示：
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
很简单，直接传递给了mDecor ，这个mDecor 就是当前窗口最顶层的DecorView 。
// This is the top-level view of the window, containing the window decor.
private DecorView mDecor;
跟进DecorView#superDispatchTouchEvent() :
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
居然是调用父类的dispatchTouchEvent() 方法，DecorView 的父类是FrameLayout ,继续跟进查看，发现FrameLayout 并没有这个方法，那就继续向上追，FrameLayout 的父类是ViewGroup ，也就是说，触摸事件经过层层传递，最终传递到ViewGroup#dispatchTouchEvent() 方法,至此，事件已经传递到视图的顶级View了。
ViewGroup对事件的分发过程
接下来是重头戏了...上代码ViewGroup#dispatchTouchEvent() ...
public boolean dispatchTouchEvent(MotionEvent ev) {
// 调试用，不去管它
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
// 辅助功能，有些用户由于视力上、身体上、年龄上使他们不能接受语音或者视觉信息
// 不是重点，也不去管它
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
boolean handled = false;
// onFilterTouchEventForSecurity(ev)，触摸事件安全过滤
// 具体实现：当窗口被遮挡，返回false，丢弃触摸事件；未被遮挡，返回true
if (onFilterTouchEventForSecurity(ev)) {
// 没有被遮挡
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// 如果是Down事件，则重置所有之前保存的状态，因为这是事件序列的开始
// mFirstTouchTarget会被设为Null
cancelAndClearTouchTargets(ev);
// 重置FLAG_DISALLOW_INTERCEPT
resetTouchState();
}
// 检测是否拦截
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
// 标记事件不允许被拦截，默认为false
// 可以由requestDisallowInterceptTouchEvent方法来设置
// 设置为true，ViewGroup将无法拦截Down以外的点击事件
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
// 调用onInterceptTouchEvent(ev)方法，询问自己是否要拦截事件
// ViewGroup的onInterceptTouchEvent(ev)方法默认返回false
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;
}
// If intercepted, start normal event dispatch. Also if there is already
// a view that is handling the gesture, do normal event dispatch.
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
// 通过标记和Action检查Cancel，将结果赋值给局部变量canceled
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// split标记是否需要将事件分发给多个子View，默认为true
// 可通过setMotionEventSplittingEnabled()方法设置
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
// 如果没取消也没拦截，进入执行语句中
if (!canceled && !intercepted) {
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
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;
// 判断newTouchTarget为Null，且ChildrenCount不为0
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
// 寻找可以处理触摸事件的子View
// 通过buildTouchDispatchChildList()方法构建子View的List集合preorderedList
final ArrayList preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
// 倒序遍历所有的子View
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
// 同时满足两种情况下子View可以接收事件的分发
// canViewReceivePointerEvents()方法会判断子View是否可见和是否在播放动画
// isTransformedTouchPointInView()方法会判断触摸事件坐标是否在子View内
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
// 查找当前子View是否在mFirstTouchTarget中存储
// mFirstTouchTarget是一种单链表结构
// 找不到则返回Null
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// newTouchTarget不为Nul，说明已经找到接收的View了，break跳出for循环
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
// 没有跳出循环，说明我们找到的Child并没有在mFirstTouchTarget中
// 调用dispatchTransformedTouchEvent()方法
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)){
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
// 将child赋值给mFirstTouchTarget
newTouchTarget = addTouchTarget(child, idBitsToAssign);
// alreadyDispatchedToNewTouchTarget赋值为true，跳出循环
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
// 没有找到可以接收事件的子View，并且之前的mFirstTouchTarget不为空
// newTouchTarget指向了最初的mFirstTouchTarget
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;
}
}
}
if (mFirstTouchTarget == null) {
// 如果mFirstTouchTarget为null
// 调用dispatchTransformedTouchEvent()方法
// 第三个参数为null，会调用super.dispatchTouchEvent()方法
// 将当前ViewGroup当做普通的View处理
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);
// 当某个手指抬起时，清除与它相关的数据
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
事件拦截
intercepted 用来标记ViewGroup 是否拦截事件，当事件为MotionEvent.ACTION_DOWN 或者mFirstTouchTarget!=null 时，if 判断成立，然后判断disallowIntercept 标志位，当disallowIntercept 为false时，调用onInterceptTouchEvent() 方法，并将返回值赋值给intercepted ，否则当disallowIntercept 为true时，则直接将intercepted 赋值为false 。
disallowIntercept 标记位可以通过公共方法 requestDisallowInterceptTouchEvent() 设置，通常由子View调用，当设置为true 后，ViewGroup 将无法拦截除ACTION_DOWN 之外的点击事件，原因是当事件为ACTION_DOWN 时，ViewGroup 会重置disallowIntercept 标记位，并且将mFirstTouchTarget 设置为null，因此，当事件为ACTION_DOWN 时，ViewGroup 总是会调用自己的onInterceptTouchEvent()方法。
if (actionMasked == MotionEvent.ACTION_DOWN) {
// 如果是Down事件，则重置所有之前保存的状态，因为这是事件序列的开始
// mFirstTouchTarget会被设为Null
cancelAndClearTouchTargets(ev);
// 重置FLAG_DISALLOW_INTERCEPT
resetTouchState();
}
// 检测是否拦截
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
// 标记事件不允许被拦截，默认为false
// 可以由requestDisallowInterceptTouchEvent方法来设置
// 设置为true，ViewGroup将无法拦截Down以外的点击事件
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
// 调用onInterceptTouchEvent(ev)方法，询问自己是否要拦截事件
// ViewGroup的onInterceptTouchEvent(ev)方法默认返回false
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;
}
事件分发
中间经过标记和action检查cancel，将结果赋值给变量canceled。if (!canceled && !intercepted) 语句表明，事件未被取消且intercepted为false(未拦截)，则会进入执行语句中。
首先判断childrenCount不为0，然后通过buildTouchDispatchChildList()方法拿到子元素的List集合，接着倒序遍历所有子元素，寻找可以接收点击事件的子元素，为什么要倒序遍历，是因为buildTouchDispatchChildList()内部会调用buildOrderedChildList()方法,该方法会将子元素根据Z轴排序，在同一Z平面上的子元素则会根据绘制的先后顺序排序，触摸的时候我们当然会希望浮在最上层的元素最先响应事件。
对于每一个子元素来说，需要canViewReceivePointerEvents()和isTransformedTouchPointInView()均返回true，才说明该子元素可以处理触摸事件，否则直接continue进行下一次循环。
canViewReceivePointerEvents()通过是否可见及是否在播放动画来判断子元素是否可以接收事件，isTransformedTouchPointInView()判断触摸事件的坐标点是否在子元素内，这样我们就获得了可以处理触摸事件的子元素。
接下来通过getTouchTarget()方法判断当前子元素是否已经赋值给mFirstTouchTarget，如果newTouchTarget不为null，说明子元素已经在mFirstTouchTarget中，执行break跳出循环。
如果newTouchTarget为null,说明子元素并没有在mFirstTouchTarget中保存，此时调用dispatchTransformedTouchEvent()方法，该方法十分重要，在该方法内部：如果子元素是ViewGroup并且事件没有被拦截，那么递归调用ViewGroup的dispatchTouchEvent();如果子元素是View，那么调用View的dispatchTouchEvent() ，最终会调用View的onTouchEvent()。
dispatchTransformedTouchEvent() 方法是有返回值的，如果返回true，说明子元素消耗了触摸事件，则在下面的代码中将子元素赋值给mFirstTouchEvent ，并跳出循环，mFirstTouchTarget是否被赋值，将直接影响到ViewGroup对事件的拦截策略，如果mFirstTouchTarget为null，那么ViewGroup就会默认拦截接下来同一序列中的所有触摸事件，这一点在后面分析;如果返回false，ViewGroup就会把事件分发给下一个子元素(如果还有下一个子元素的话)。
// 如果没取消也没拦截，进入方法体中
if (!canceled && !intercepted) {
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
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;
// 判断newTouchTarget为Null，且ChildrenCount不为0
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
// 寻找可以接受触摸事件的子View
// 通过buildTouchDispatchChildList()方法构建子View的List集合preorderedList
final ArrayList preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
// 倒序遍历所有的子View
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
// 同时满足两种情况下子View可以接收事件的分发
// canViewReceivePointerEvents()方法会判断子View是否可见和是否在播放动画
// isTransformedTouchPointInView()方法会判断触摸事件坐标是否在子View内
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
// 查找当前子View是否在mFirstTouchTarget中存储
// 找不到则返回Null
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// newTouchTarget不为Nul，说明已经找到接收的View了，break跳出for循环
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
// 没有跳出循环，说明我们找到的Child并没有在mFirstTouchTarget中
// 调用dispatchTransformedTouchEvent()方法
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)){
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
// 将child赋值给mFirstTouchTarget
newTouchTarget = addTouchTarget(child, idBitsToAssign);
// alreadyDispatchedToNewTouchTarget赋值为true，跳出循环
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
当没有任何子元素处理触摸事件时，调用dispatchTransformedTouchEvent() 方法，注意此时第三个参数传入null，在方法内部就会调用super.dispatchTouchEvent() ,也就是View类的dispatchTouchEvent() 。
if (mFirstTouchTarget == null) {
// 如果mFirstTouchTarget为null
// 调用dispatchTransformedTouchEvent()方法
// 第三个参数为null，会调用super.dispatchTouchEvent()方法
// 将当前ViewGroup当做普通的View处理
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
onInterceptTouchEvent() 方法
if语句判断触摸事件来源是否为鼠标或其他指针式设备，其他情况下默认返回false 。
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
&& ev.getAction() == MotionEvent.ACTION_DOWN
&& ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
&& isOnScrollbarThumb(ev.getX(), ev.getY())) {
return true;
}
return false;
}
dispatchTransformedTouchEvent() 方法
dispatchTransformedTouchEvent() 源码中发现多次对于传入的child是否为null做判断，并且都做类似的操作：
当child==null时，调用super.dispatchTouchEvent()，也就是View类的dispatchTouchEvent()方法，因为ViewGroup的父类是View，最终会调用View的onTouchEvent()方法。
当child!=null时，递归调用child.dispatchTouchEvent()，此时child可能是View，也可能是ViewGroup。
从源码中可以看出dispatchTransformedTouchEvent() 方法的返回值，最终取决于onTouchEvent()方法，也就是说，onTouchEvent()是否消费了事件，决定了dispatchTransformedTouchEvent() 方法的返回值，从而决定mFirstTouchTarget是否为null 。因为如果dispatchTransformedTouchEvent() 方法的返回值为false，就无法执行addTouchTarget()方法，而mFirstTouchTarget就是在该方法中被赋值的。
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;
}
重要结论
-
ViewGroup一旦拦截ACTION_DOWN事件，那么当ACTION_MOVE、ACTION_UP事件到来时，将不再调用ViewGroup的onInterceptTouchEvent()方法，并且同一序列中的其他事件都会默认交给它处理。分析：
ViewGroup拦截ACTION_DOWN事件，会导致intercepted为true，从而导致if (!canceled && !intercepted)判断不成立，跳过执行语句，mFirstTouchTarget也为null。那么当ACTION_MOVE、ACTION_UP事件到来时，if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null)判断语句不成立，会直接将intercepted赋值为true，即默认拦截后续的所有事件。 -
某个
View一旦开始处理事件，如果它不消费ACTION_DOWN事件，那么同一事件序列中的其他事件也不会再交给它来处理，并且事件将重新交给它的父容器去处理。分析：某个
View不消费ACTION_DOWN事件，即dispatchTransformedTouchEvent()方法返回了false，导致if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign))判断语句不成立，跳过执行语句，同样导致mFirstTouchTarget为null，那么和第一条结论的分析一样，当ACTION_MOVE、ACTION_UP事件到来时，if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null)判断语句不成立，同样会直接将intercepted赋值为true，所以后续的事件都无法传递到这个View，而是交给ViewGroup处理。 ViewGroup(绝大多数情况下)默认不拦截任何事件。Android源码中ViewGroup的onInterceptTouchEvent()方法默认返回false。ViewGroup没有重写父类View的onTouchEvent()方法。
- 到这里就分析完了，查了很多资料，中间也有可能有理解错误的地方，如果哪里错了，还请大家指正，谢谢。
- Github