先借助于A、B、C三层假想的view进行一定场景下的事件分发机制分析，然后在深入到源码中。
一、事件是由外向内传递的，下面的事件传递流程是A-B-C,A是最外层view，其次是B，最里层的是C，下面从B开始进行分析。
2、如果onInterceptTouchEvent返回true则拦截事件，事件由B处理，不会往下继续传递给C，C不会在接受到任何的事件，而会调用B的onTouchEvent方法，如果onTouchEvent返回true,则down事件结束，被B消费掉了【后续的move和up事件有可能会到达B，也有可能到达不了B，因为要看A是否拦截move和up事件】，如果onTouchEvent返回false，则down事件会向A回传调用A的onTouchEvent方法，后续的move和up事件也不会在到达B了。
3、如果onInterceptTouchEvent返回false则不拦截事件，事件继续向下传递，传递到C，会调用C的dispatchTouchEvent方法。C是一个view没有onInterceptTouchEvent方法，会直接调用C的onTouchEvent方法，后面的流程就跟B一样了。这样一个down事件就由上层view传递给了下一级子View了。
4、如果B和C之间还有多层view【容器】嵌套，其分发流程是跟B传到C的流程是一样的，就这样循环下去，直到完成整个事件分发过程。
1、根据源码：
// 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;
}
由上面的源码可知，只有当事件类型是down事件或者mFirstTouchTarget != null时才会执行onInterceptTouchEvent方法。
2、如果C没有消费down事件，那么mFirstTouchTarget就为null。所以如果在down事件到来时，B拦截了该事件，那么mFirstTouchTarget就为nul，那么后续move和up事件到来时，就不会去调用自身的onInterceptTouchEvent方法了，而是直接就处理了move和up事件。
3、如果C消费了down事件，那么mFirstTouchTarget != null，如果move和up事件到达B时，B还是会调用onInterceptTouchEvent去判断是否需要拦截，如果不拦截，就会继续传递给C去处理。
4、由上可知，如果C没有消费down事件，那么后续它也不会在接受到任何事件了。如果C消费了down事件，那么后续的move和up事件由可能交给C去处理，也有可能被B拦截掉。这样就有了一种解决BC事件冲突的一种思路了：B不要拦截down事件，C要消费掉down事件，move事件和up事件可以根据具体的业务逻辑去判断B到底要不要拦截【是交给B处理还是交给C处理】。
三、还有一种情况，就是使用requestDisallowInterceptTouchEvent方法，通过requestDisallowInterceptTouchEvent来设置FLAG_DISALLOW_INTERCEPT标记位到达目的，这个方法在子view 中使用以达到能影响上层view的事件分发过程的效果。如果子view中调用该方法并设置值为true，那么上层view将不能拦截除了down事件以外的事件，不能拦截down事件的原因：
根源源码：
// 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();
}
由源码可知，如果是down事件，那么上层view会在resetTouchState方法中重置FLAG_DISALLOW_INTERCEPT，这样就导致设置requestDisallowInterceptTouchEvent是无效的。
四、根据上面的分析可知，上层view一旦拦截了down事件，那么其子view将永远不会在接受到任何事件了。所以如果不是确定需要，一般不要在上层view中拦截down事件，而将down事件交给子view去处 理，这样后续的move事件就可以灵活的根据业务逻辑去分发了（onInterceptTouchEvent和requestDisallowInterceptTouchEvent配合着去处理move事件）。
五、从源码角度分析view的事件分发机制：
1、view的dispatchTouchEvent和onTouchEvent、以及其他相关的源码
/**
* 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 the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
// We don't have focus or no virtual descendant has it, do not handle the event.
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// We have focus and got the event, then use normal event dispatch.
event.setTargetAccessibilityFocus(false);
}
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
//关键代码
if (onFilterTouchEventForSecurity(event)) {
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
/**
* 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) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
//如果view的Enabled为false，就直接返回，不会继续执行了
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return (((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
//如果view的Enabled为true，就继续进行下面操作
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
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()) {
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);
}
//此段代码会调用view的OnClickListener
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
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)) {
performClick();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
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) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0);
}
break;
case MotionEvent.ACTION_CANCEL:
setPressed(false);
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_MOVE:
drawableHotspotChanged(x, y);
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback();
setPressed(false);
}
}
break;
}
return true;
}
return false;
}
/**
* Call this view's OnClickListener, if it is defined. Performs all normal
* actions associated with clicking: reporting accessibility event, playing
* a sound, etc.
*
* @return True there was an assigned OnClickListener that was called, false
* otherwise is returned.
*/
public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
return result;
}
/**
* Register a callback to be invoked when this view is clicked. If this view is not
* clickable, it becomes clickable.
*
* @param l The callback that will run
*
* @see #setClickable(boolean)
*/
public void setOnClickListener(@Nullable OnClickListener l) {
if (!isClickable()) {
setClickable(true);
}
getListenerInfo().mOnClickListener = l;
}
2、结合上面的源码进行view的事件分发机制的分析
控制view事件分发的方法：dispatchTouchEvent onTouchEvent
对view事件分发有影响的设置： Enabled(View是否可用) Clickable和OnClickListener(View是否可点击) OnTouchListener(View是否设置了touch监听)根据这些因素进行 分情况分析：
A、如果view设置了OnTouchListener，并且view的Enabled是true，并且OnTouchListener的onTouch返回值是true，那么就不会在执行view的onTouchEvent方法，
此时dispatchTouchEvent的返回值是true。
B、如果A中的前提条件有一个不成立，那么就会执行view的onTouchEvent方法，此时dispatchTouchEvent的返回值由onTouchEvent的返回值决定。
C、由onTouchEvent和performClick的源码可知，OnClickListener是在onTouchEvent中调用的，所以OnTouchListener会先于OnClickListener执行，如OnTouchListene返 回true，就不会在调用OnClickListener了。
D、如果view的Enabled为false，dispatchTouchEvent里就不会在调用OnTouchListener了（view不会响应OnTouchListener事件了），onTouchEvent就直接返回，不会继 续往下执行了，OnClickListener也不会执行了（view不会响应OnClickListener事件）。此时onTouchEvent的返回值由Clickable决定了，如果Clickable是true就返回 true，否则返回false。
E、如果view的Enabled为true，并且走进了onTouchEvent方法中，那么onTouchEvent方法的返回值仍然是由Clickable决定的。
F、Enabled会影响是否响应OnTouchListener和OnClickListener事件，Clickable会影响onTouchEvent的返回值。
J、在view的setOnClickListener方法中会把Clickable设置为true,会影响Clickable的值。
H、在down的时候，dispatchTouchEvent返回了false，就不会在接受到后面的MOVE、UP等其他事件了。
六、viewGroup的dispatchTouchEvent源码分析：
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
// If the event targets the accessibility focused view and this is it, start
// normal event dispatch. Maybe a descendant is what will handle the click.
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
//handled记录最终的返回结果，也就是是否消费
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
//如果是ACTION_DOWN事件，进行初始化和重置
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) { //只有是down事件才能走进来
// 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.
//清空mFirstTouchTarget链表,将mFirstTouchTarget置为null
cancelAndClearTouchTargets(ev);
//重置了disallowIntercept对应的标志位，这个标志位决定了是否允许父view拦截事件
resetTouchState();
}
//判断是否拦截的标志位，true拦截，false不拦截。
// Check for interception.
final boolean intercepted;
//如果是ACTION_DOWN事件，或者是MOVE、UP等其他事件时mFirstTouchTarget不为空(即已经有消费事件的目标view了)就会走到if里面去判断是否拦截
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//disallowIntercept可以通过requestDisallowInterceptTouchEvent方法来设置，如果设置为true，就是子view通知父View不要拦截该事件。
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
//如果disallowIntercept为true，那么就不会执行onInterceptTouchEvent(ev)方法了，直接将intercepted设置为false。否则会判断onInterceptTouchEvent(ev)。
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.
//如果不是down事件，并且没有消费事件的目标view（即mFirstTouchTarget为空），那就直接拦截下来，ViewGroup自己处理。
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);
}
//判断是否是cancel事件
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
//控制多点触摸标志位
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
//保存消费事件的目标View所对应的TouchTarget对象
TouchTarget newTouchTarget = null;
//标志事件是否已经分发到了目标View中
boolean alreadyDispatchedToNewTouchTarget = false;
//如果没有取消，并且没有拦截，就会走进去
if (!canceled && !intercepted) {
// If the event is targeting accessiiblity focus we give it to the
// view that has accessibility focus and if it does not handle it
// we clear the flag and dispatch the event to all children as usual.
// We are looking up the accessibility focused host to avoid keeping
// state since these events are very rare.
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
//只有ACTION_DOWN事件才会执行if里面的代码，其他事件不执行(后面的两个条件不需要关心),这里面的是down事件的递归分发，去寻找消费事件的目标view的操 作
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 ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
//遍历子View，递归寻找消费该down事件的目标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;
}
//判断事件是否落在当前子view的区域内，如果没有就continue继续查找下个子view，如果落在了当前子view的区域内，就继续往下走
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//用于多点触摸
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);
//在dispatchTransformedTouchEvent中调用子view的dispatchTouchEvent继续向下分发，如果返回true，说明子view消费了该事件，就走if里面
//这个方法后面会介绍
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();
//将消费事件的子view添加到mFirstTouchTarget中
newTouchTarget = addTouchTarget(child, idBitsToAssign);
//是否已经分发到了目标View中的标志设置为true
alreadyDispatchedToNewTouchTarget = true;
//找到了消费事件的目标子view就不需要在进行循环了，直接break跳出循环
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();
}
//正常情况下这段代码不会执行
//因为只有down事件才能走到这，根据newTouchTarget = addTouchTarget(child, idBitsToAssign)可知，newTouchTarget和mFirstTouchTarget会同时为空或不为空
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;
}
}
}
//如果mFirstTouchTarget为空，说明没有找到消费事件的目标子view，那就走if里面直接自己处理事件
// 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 {
//走到这里面，说明已经有处理事件的目标view了
// 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;
//如果是down事件，那么if条件就会成立，直接返回true给上层（如果不是down事件，会把newTouchTarget置空，把alreadyDispatchedToNewTouchTarget设置为 false）
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
/ /如果intercepted为true，也就是当前viewgroup拦截了事件，那么就会给子view分发一个cancel事件（dispatchTransformedTouchEvent里面）
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//将move、up等事件分发给子view，如果cancelChild为true，子view就会收到一个cancle事件，否则就是正常的move、up事件继续往下传递
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
//如果intercepted为true就会销毁mFirstTouchTarget，这就是为什么父view拦截之后，目标子view就不会在收到后续事件了
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;
}
//上面很多地方用到了这个方法，就看一下这个方法，这个方法就是做事件递归分发的方法，方法里分为3块内容，一个是cancel、一个是多点触控、一个是down、move、up 等正常的事件分发
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();
//如果cancel为true，就走到if里面，将事件设置为cancel事件分发下去，这就是为什么事件被拦截之后，之前处理过该事件的目标子View会收到cancel事件
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
//如果没有目标子view，这个cancel事件就自己处理，最终会调用view的dispatchTouchEvent(event）方法
handled = super.dispatchTouchEvent(event);
} else {
//如果有目标子view，就将这个cancel事件递归分发下去
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
//多点触摸需要
// 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);
}
//正常的事件分发代码
// Perform any necessary transformations and dispatch.
if (child == null) {
//如果没有目标子view，这个事件就自己处理
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());
}
//如果有目标子view，就将这个事件递归分发下去
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}