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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；
@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<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);
}
}
正文完
