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。
1、action_down事件到达B时，会调用B的dispatchTouchEvent方法，然后会在dispatchTouchEvent内部调用onInterceptTouchEvent方法判断是否要拦截事件。 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。二、B的onInterceptTouchEvent方法并不是在每一个事件中都会执行的，它的执行是有条件的，下面说明原因： 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; }