ps：本文系为转载文章，浏览原文可读性会更好，文章开端有原文链接
ps：源码是基于 android api 27 来剖析的
这一篇是继Android中ViewGroup的dispatchTouchEvent办法源码剖析（一）来写的，首先咱们先把 ViewGroup的dispatchTouchEvent 办法源码全部列进去；
@Overridepublic boolean dispatchTouchEvent(MotionEvent ev) { //6、 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); } //7、 boolean handled = false; //8、 if (onFilterTouchEventForSecurity(ev)) { final int action = ev.getAction(); //9、 final int actionMasked = action & MotionEvent.ACTION_MASK; //10、 // 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(); } //11、 // Check for interception. final boolean intercepted; //12、 if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { //13、 final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { //14、 intercepted = onInterceptTouchEvent(ev); //15、 ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } //16、 } 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); } //17、 // Check for cancelation. final boolean canceled = resetCancelNextUpFlag(this) || actionMasked == MotionEvent.ACTION_CANCEL; //18、 // Update list of touch targets for pointer down, if needed. final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0; //19、 TouchTarget newTouchTarget = null; //20、 boolean alreadyDispatchedToNewTouchTarget = false; //21、 if (!canceled && !intercepted) { //21、 // 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; if (actionMasked == MotionEvent.ACTION_DOWN || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { //22、 final int actionIndex = ev.getActionIndex(); // always 0 for down //23、 final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex) : TouchTarget.ALL_POINTER_IDS; //24、 // Clean up earlier touch targets for this pointer id in case they // have become out of sync. removePointersFromTouchTargets(idBitsToAssign); final int childrenCount = mChildrenCount; //25、 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(); //26、 final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled(); //27、 final View[] children = mChildren; for (int i = childrenCount - 1; i >= 0; i--) { //28、 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; } //29、 if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); continue; } //30、 newTouchTarget = getTouchTarget(child); //31、 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; } //32、 resetCancelNextUpFlag(child); //33、 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(); newTouchTarget = addTouchTarget(child, idBitsToAssign); 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(); } //34、 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; } } } //35、 // Dispatch to touch targets. if (mFirstTouchTarget == null) { //36、 // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); //37、 } else { //38、 // 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 { //39、 final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted; //40、 if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) { handled = true; } //41、 if (cancelChild) { //42、 if (predecessor == null) { mFirstTouchTarget = next; //43、 } else { predecessor.next = next; } target.recycle(); target = next; continue; } } //44、 predecessor = target; target = next; } } //45、 // Update list of touch targets for pointer up or cancel, if needed. if (canceled || actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { resetTouchState(); //46、 } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) { final int actionIndex = ev.getActionIndex(); final int idBitsToRemove = 1 << ev.getPointerId(actionIndex); removePointersFromTouchTargets(idBitsToRemove); } } //47、 if (!handled && mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1); } return handled;}咱们接着Android中ViewGroup的dispatchTouchEvent办法源码剖析（一）文章没有剖析完的代码进行剖析；
//21、 if (!canceled && !intercepted) { ...... //25、 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(); //26、 final boolean customOrder = preorderedList == null && isChildrenDrawingOrderEnabled(); //27、 final View[] children = mChildren; for (int i = childrenCount - 1; i >= 0; i--) { //28、 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; } //29、 if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); continue; } //30、 newTouchTarget = getTouchTarget(child); //31、 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; } //32、 resetCancelNextUpFlag(child); //33、 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(); newTouchTarget = addTouchTarget(child, idBitsToAssign); 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(); } ...... } }正文25 示意如果新的触摸对象为 null 并且以后 ViewGroup 有子元素；正文26 示意是否应用自定义的程序来增加控件，能够了解为是否依照 draw 的程序；正文27 示意 ViewGroup 的子元素数组；正文28 能够了解为如果是用了自定义的程序来增加控件，那么绘制的 View 的程序和 mChildren 的程序是不一样的，因而依据 getChildDrawingOrder 办法取出真正的绘制的 View；正文29 示意如果 child 不能够接管这个触摸的事件，即 child 不是 visiable，或者是否没有动画，也就是判断 x, y 是否没有在 view 的区域内，这就是为什么补间动画的触发区域不随着动画而扭转的起因了；正文30 示意查找 child 是否曾经记录在 mFirstTouchTarget 这个单链表中；正文31 示意果新的触摸指标对象不为空，那么就把这个触摸的 id 赋予它；正文32 示意子 View 如果不在之前的触摸指标列表中，就会重置子 view 的标记；正文33 示意将相应的事件传递上来，不过 event 被传递给 child 的时候将会做相应偏移，假如子 View 接管并且解决了这个事件，那么就更新上一次触摸事件的信息，并且会创立一个新的触摸指标对象，给这个子 view 和 pointer 的 id 进行绑定。
...... //21、 if (!canceled && !intercepted) { ...... if (actionMasked == MotionEvent.ACTION_DOWN || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { ...... //34、 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; } } } ......正文34 示意如果没有 child 响应该事件，则将此事件交给最近退出的 target。
...... //35、 // Dispatch to touch targets. if (mFirstTouchTarget == null) { //36、 // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); //37、 } else { //38、 // 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; //38A、 if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { //39、 final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted; //40、 if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) { handled = true; } //41、 if (cancelChild) { //42、 if (predecessor == null) { mFirstTouchTarget = next; //43、 } else { predecessor.next = next; } target.recycle(); target = next; continue; } } //44、 predecessor = target; target = next; } } ......正文35 示意如果没有能响应该事件的 child，那么就会调用以后 ViewGroup 的 onTouchEvent 办法；正文36 示意 child 响应该事件；正文38A 示意如果曾经将这个事件交给 newTouchTarget 解决过了，就不反复解决了，也就是如果在Android中ViewGroup的dispatchTouchEvent办法源码剖析（一）这篇文章正文33 所在的代码解决过了；正文39 示意是否让 child 勾销处理事件，如果是，则会分发给 child 一个 ACTION_CANCEL 事件；正文40 示意进行事件的散发；正文41 示意如果以后的 child 失去的是一个ACTION_CANCEL 事件；正文42 示意如果以后是第一个 TouchTarget，那么就把头去掉（predecessor 是一个单链表）；正文43 示意把下一个赋予父节点的上一个，这样就把以后节点给丢掉；正文44 示意如果没有删除这个节点，那么下一轮父节点就是以后节点。
...... //45、 // Update list of touch targets for pointer up or cancel, if needed. if (canceled || actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { resetTouchState(); //46、 } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) { final int actionIndex = ev.getActionIndex(); final int idBitsToRemove = 1 << ev.getPointerId(actionIndex); removePointersFromTouchTargets(idBitsToRemove); } ......正文45 示意 如果遇到了勾销事件、或是单点触摸条件下手指来到，那么就要更新触摸的状态；如果是多点触摸下的手指抬起事件，就会依据 idBitsToRemove 从 TouchTarget 中移除掉对应的触摸点。
ViewGroup 的 dispatchTouchEvent 办法的代码能够用上面的伪代码示意；
public boolean dispatchTouchEvent(MotionEvent event) {
boolean isIntercept =false; if(onInterceptTouchEvent(event)){ isIntercept=true； } if(!isIntercept){ boolean consume= child.dispatchTouchEvent(event); if(!consume){ mFirstTouchTarget = null; }else{ mFirstTouchTarget = addTouchTarget(child, idBitsToAssign); } }else{ mFirstTouchTarget = null; } if(mFirstTouchTarget!=null){ return true; }else{ return onTouchEvent(event); }}