ps：本文系为转载文章，阅读原文可读性会更好，文章末尾有原文链接
ps：源码是基于 android api 27 来分析的
这一篇是继Android中ViewGroup的dispatchTouchEvent方法源码分析（一）来写的，首先我们先把 ViewGroup的dispatchTouchEvent 方法源码全部列出来；
@Override
public 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 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;
}
我们接着Android中ViewGroup的dispatchTouchEvent方法源码分析（一）文章没有分析完的代码进行分析；
//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 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();
}
......
}
}
注释25 表示如果新的触摸对象为 null 并且当前 ViewGroup 有子元素；注释26 表示是否使用自定义的顺序来添加控件，可以理解为是否按照 draw 的顺序；注释27 表示 ViewGroup 的子元素数组；注释28 可以理解为如果是用了自定义的顺序来添加控件，那么绘制的 View 的顺序和 mChildren 的顺序是不一样的，因此根据 getChildDrawingOrder 方法取出真正的绘制的 View；注释29 表示如果 child 不可以接收这个触摸的事件，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改变的原因了；注释30 表示查找 child 是否已经记录在 mFirstTouchTarget 这个单链表中；注释31 表示果新的触摸目标对象不为空，那么就把这个触摸的 id 赋予它；注释32 表示子 View 如果不在之前的触摸目标列表中，就会重置子 view 的标志；注释33 表示将相应的事件传递下去，不过 event 被传递给 child 的时候将会做相应偏移，假设子 View 接收并且处理了这个事件，那么就更新上一次触摸事件的信息，并且会创建一个新的触摸目标对象，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;
}
}
}
......
注释34 表示如果没有 child 响应该事件，则将此事件交给最近加入的 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;
}
}
......
注释35 表示如果没有能响应该事件的 child，那么就会调用当前 ViewGroup 的 onTouchEvent 方法；注释36 表示 child 响应该事件；注释38A 表示如果已经将这个事件交给 newTouchTarget 处理过了，就不重复处理了，也就是如果在Android中ViewGroup的dispatchTouchEvent方法源码分析（一）这篇文章注释33 所在的代码处理过了；注释39 表示是否让 child 取消处理事件，如果是，则会分发给 child 一个 ACTION_CANCEL 事件；注释40 表示进行事件的分发；注释41 表示如果当前的 child 得到的是一个ACTION_CANCEL 事件；注释42 表示如果当前是第一个 TouchTarget，那么就把头去掉（predecessor 是一个单链表）；注释43 表示把下一个赋予父节点的上一个，这样就把当前节点给丢掉；注释44 表示如果没有删除这个节点，那么下一轮父节点就是当前节点。
......
//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);
}
......
注释45 表示 如果遇到了取消事件、或是单点触摸条件下手指离开，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，就会根据 idBitsToRemove 从 TouchTarget 中移除掉对应的触摸点。
ViewGroup 的 dispatchTouchEvent 方法的代码可以用下面的伪代码表示；
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);
}
}