touch事件传递，这里有三个关键的方法，分别是dispatchTouchEvent、onInterceptTouchEvent、onTouchEvent，其中View和Activity没有onInterceptTouchEvent，只有ViewGroup三个方法都有。调用过程是：dispatch(分发)->intercept(是否拦截)->ontouch(处理)。事件由Activity经ViewGroup传递到View，如果一路事件都没有被消费掉，那么事件又会由View经ViewGroup传递到Activity直到被处理掉。View的dispatchTouchEvent是将事件分发给了自己。
二、重写onInterceptTouchEvent返回true(默认false)，则后续事件不会往下dispatch，子控件的diaptchTouchEvent无法接受touch事件；如果此时没有重写onTouchEvent，使之返回true，那么ACTION_DOWN将有父控件中onTouchEvent返回true的父控件处理，或者一直传递到Activity，由Activity处理；需要特别注意的是：假设A处理了ACTION_DOWN事件，则后续的ACTION_MOVE、ACTION_UP事件也由A处理！！
三、dispatchTouchEvent的调用逻辑，如果是ViewGroup，则先调用自己的onInterceptTouchEvent,如果是true,则直接返回；如果是false，则调用子View/ViewGroup的dispatchTouchEvent事件，如果子组件没有消费掉事件，则返回到本组件的onTouchEvent，则返回onTouchEvent的返回值！！
四、只重写onTouchEvent，使之返回true，表示消费了该touch事件，需要特别注意的是：假设ViewGroup A处理了ACTION_DOWN事件，不光是后续的ACTION_MOVE、ACTION_UP事件也由A处理，甚至子View的dispatchTouchEvent都不会调用，因为此时本View的dispatchTouchEvent返回true，表示事件已经被handled
五、不管是重写onTouchEvent返回true，还是重写onIterceptTouchEvent返回true，都说明事件已经不需要往子view传递了，此时子view的dispatchTouchEvent将无法收到事件。如果onIterceptTouchEvent返回true,而onTouchEvent没有重写，则事件会继续往父控件传递，直到某个父控件消费了事件，或者传递到Activity，由Activity消费掉。
六、在onTouchEvent中返回true，消费了事件，则事件不会再往上级组件传递；但是依然会调用父控件、Activity的dispatchTouchEvent事件，也就是说父控件还是有机会拦截事件的。
七、在dispatchTouchEvent中返回true(默认返回false)，表示该事件已经被handled，不再继续分发；这样事件不会向传递给父控件处理，不管有没重写本组件的onTouchView消费该事件。
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
...
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
...
// Check for interception.
final boolean intercepted;
//ViewGroup去判断这个事件该不该去拦截，首先是这个事件得是ACTION_DOWN事件或者该事件的mFirstTouchTarget（目标子View）是不为空的才会考虑要不要拦截。***这说明mFirstTouchTarget为空的情况下，ACTION_MOVE和ACTION_UP事件是不会经过这个拦截判断的，而是直接intercepted = true表示事件被直接拦截掉。
// 那么mFirstTouchTarget（目标子View）这个变量到底是什么呢？什么时候会为空呢？
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//这个变量是控制是不是不允许父控件去拦截该事件的，取值是看"mGroupFlags"的取值，这里面涉及到一个方法：requestDisallowInterceptTouchEvent()方法。这个方法确定"mGroupFlags"的取值，控制请求父布局不拦截该事件，而是交给自己去做处理。这个方法在处理滑动冲突等场景时经常用到。
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;
}
...
if (!canceled && !intercepted) {
// If the event is targeting accessibility 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.
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;
}
if (!child.canReceivePointerEvents()
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
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);
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();
}
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;
}
}
}
// 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 {
// 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 {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
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;
}
默认流程
Touch默认流程.png
dispatchTouchEvent()中调用了dispatchTransformedTouchEvent()方法，dispatchTransformedTouchEvent()调用了super.dispatchTouchEvent()方法，所以如果重写dispatchTouchEvent方法：
-
返回true
dispatchTouchEvent返回true.png
-
返回false
dispatchTouchEvent返回false.png
onInterceptTouchEvent
-
返回true
onInterceptTouchEvent返回true.png
-
返回false
onInterceptTouchEvent和onTouchEvent如果返回false的话， 效果和默认的一样
onTouchEvent
-
返回true
onTouch返回true.png
-
返回false
onTouch返回false.png
参考：
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