Activity中
当屏幕有touch事件时，首先调用Activity的dispatchTouchEvent方法
/**
* Called to process touch screen events. You can override this to
* intercept all touch screen events before they are dispatched to the
* window. Be sure to call this implementation for touch screen events
* that should be handled normally.
*
* @param ev The touch screen event.
*
* @return boolean Return true if this event was consumed.
*/
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
只有ACTION_DOWN事件派发时调运了onUserInteraction方法，直接跳进去可以看见是一个空方法。接着往下看
首先分析Activity的attach方法可以发现getWindow()返回的就是PhoneWindow对象（PhoneWindow为抽象Window的实现子类），那就简单了，也就相当于PhoneWindow类的方法，而PhoneWindow类实现于Window抽象类，所以先看下Window类中抽象方法的定义，如下：
<span style="font-size:24px;">/**
* Used by custom windows, such as Dialog, to pass the touch screen event
* further down the view hierarchy. Application developers should
* not need to implement or call this.
*用户不需要重写实现的方法，实质也不能，在Activity中没有提供重写的机会，因为Window是以组</span><pre name="code" class="java"><span style="font-size:24px;">*</span><span style="font-family: Arial, Helvetica, sans-serif;"><span style="font-size:18px;">合模式与Activity建立关系的</span></span>
*/ public abstract boolean superDispatchTouchEvent(MotionEvent event);
PhoneWindow里看下Window抽象方法的实现：
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
这里出现了mDecor变量，是啥？其实是DecorView的实例，有人会问DecorView又是啥？
在PhoneWindow类里发现，mDecor是DecorView类的实例，同时DecorView是PhoneWindow的内部类。最惊人的发现是DecorView extends FrameLayout implements RootViewSurfaceTaker，看见没有？它是一个真正Activity的root view,它继承了FrameLayout。
不知道大家是不是熟悉Android App开发技巧中关于UI布局优化使用的SDK工具Hierarchy Viewer，打开的时候在最上面会有个DecorView$PhoneWindow的框框
Activity中setContentView时，把我们编写的xmlLayout文件放置在一个id为content的FrameLayout的布局（DecorView）中，这也就是为啥Activity的setContentView方法叫set content view了，就是把我们的xml放入了这个id为content的FrameLayout中
讲完了DecorView，我们在来看看mDecor.superDispatchTouchEvent(event)：
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
上面PhoneWindow的superDispatchTouchEvent直接返回了DecorView的superDispatchTouchEvent，而DecorView又是FrameLayout的子类，FrameLayout又是ViewGroup的子类，touch事件就被分发到的我们们定义的xmlLayout布局中。接下来分析ViewGroup的事件分发。
Activity的dispatchTouchEvent方法的if (getWindow().superDispatchTouchEvent(ev))本质执行的是一个ViewGroup的dispatchTouchEvent方法（这个ViewGroup是Activity特有的root view，也就是id为content的FrameLayout布局）
在Activity的触摸屏事件派发中：Activity,PhoneWindow,DecorView,ViewGroup
1,首先会触发Activity的dispatchTouchEvent方法。
2,dispatchTouchEvent方法中如果是ACTION_DOWN的情况下会接着触发onUserInteraction方法。
3,接着在dispatchTouchEvent方法中会通过Activity的root View（id为content的FrameLayout），实质是ViewGroup，通过super.dispatchTouchEvent把touchevent派发给各个activity的子view，也就是我们再Activity.onCreat方法中setContentView时设置的view。
4，若Activity下面的子view拦截了touchevent事件(返回true)则Activity.onTouchEvent方法就不会执行。
ViewGroup中
既然Activity中的DecorView是ViewGroup的子类调用了dispatchTouchEvent方法，来看看这个方法：
@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);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
/*清除以往的Touch状态然后开始新的手势。在这里你会发现cancelAndClearTouchTargets(ev)方法中有一个非常重要的操作就是将mFirstTouchTarget设置为了null（刚开始分析大眼瞄一眼没留意，结果越往下看越迷糊，所以这个是分析ViewGroup的dispatchTouchEvent方法第一步中重点要记住的一个地方），接着在resetTouchState()方法中重置Touch状态标识。*/
// 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();
}
// Check for interception.检查拦截
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {// 说明当事件为ACTION_DOWN或者mFirstTouchTarget不为null(即已经找到能够接收touch事件的目标组件)时if成立，否则if不成立，然后将intercepted设置为true，也即拦截事件
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) { // 如果没有禁止拦截，就调用onInterceptTouchEvent方法，touch事件就继续传递给子View，默认不拦截
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed存储动作以防止它改变
} else {
intercepted = false; // 如果禁止拦截，intercepted就是false，touch事件就继续传递给子View
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.如果没有touch目标组件和down事件，这个viewgroup就是继续拦截touch
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);
}
// Check for cancelation.检查取消，然后将结果赋值给局部boolean变量canceled
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed. 默认是true，作用是是否把事件分发给多个子View
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) { // 如果没有被取消也没有被拦截，就开始进行分发事件了
// 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) {
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) { // childrenCount个数是否不为0且新的touch target是空，目的就是为了找到touch target
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 = buildOrderedChildList();//子View的list集合preorderedList
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {//for循环i从childrenCount - 1开始遍历到0，倒序遍历所有的子view
final int childIndex = customOrder
? getChildDrawingOrder(childrenCount, i) : i;
final View child = (preorderedList == null)
? children[childIndex] : preorderedList.get(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 (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child); //这一句很重要，通过getTouchTarget去查找当前子View是否在mFirstTouchTarget.next这条target链中的某一个target中，如果在则返回这个target，否则返回null
if (newTouchTarget != null) {//找到了接收Touch事件的子View，即newTouchTarget，那么，既然已经找到了，所以执行break跳出for循环
// 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);
/**
*调用方法dispatchTransformedTouchEvent()将Touch事件传递给特定的子View。该方法十分重要，在该方法中为一个递归调用，会递归调用 dispatchTouchEvent()方法。在dispatchTouchEvent()中如果子View为ViewGroup并且Touch没有被拦截那么递归调用dispatchTouchEvent()，如果子View为View那么就会调用其onTouchEvent()。dispatchTransformedTouchEvent方法如果返回true则表示子View消费掉该事件，同时进入该if判断。满足if语句后重要的操作有：
1,给newTouchTarget赋值；
2,给alreadyDispatchedToNewTouchTarget赋值为true；
3,执行break，因为该for循环遍历子View判断哪个子View接受Touch事件，既然已经找到了就跳出该外层for循环；
*/
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;
}
}
}
/**
*因为在dispatchTransformedTouchEvent()会调用递归调用dispatchTouchEvent()和onTouchEvent()，所以dispatchTransformedTouchEvent()的返回值实际上是由
onTouchEvent()决定的。简单地说onTouchEvent()是否消费了Touch事件的返回值决定了dispatchTransformedTouchEvent()的返回值，从而决定mFirstTouchTarget是否为null，进一步决定了ViewGroup 是否处理Touch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 {
// 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;
}
ViewGroup中的onInterceptTouchEvent
/**
* Implement this method to intercept all touch screen motion events. This
* allows you to watch events as they are dispatched to your children, and
* take ownership of the current gesture at any point.
*实现这个方法拦截屏幕的所有触摸事件，这就允许你观察这些事件被分发给你的孩子，在任何一个点掌控当前手势
* <p>Using this function takes some care, as it has a fairly complicated
* interaction with {@link View#onTouchEvent(MotionEvent)
* View.onTouchEvent(MotionEvent)}, and using it requires implementing
* that method as well as this one in the correct way. Events will be
* received in the following order:
*使用这个函数要小心，它和View的onTouchEvent有十分复杂的交互，事件能够按照下列的顺序被收到:
* <ol>
* <li> You will receive the down event here.1,你将先收到down事件
* <li> The down event will be handled either by a child of this view
* group, or given to your own onTouchEvent() method to handle; this means
* you should implement onTouchEvent() to return true, so you will
* continue to see the rest of the gesture (instead of looking for
* a parent view to handle it). Also, by returning true from
* onTouchEvent(), you will not receive any following
* events in onInterceptTouchEvent() and all touch processing must
* happen in onTouchEvent() like normal.
* 2，down事件要么被子View的handle,要么被这个viewgroup的onTouchEvent方法处理
* <li> For as long as you return false from this function, each following
* event (up to and including the final up) will be delivered first here
* and then to the target's onTouchEvent().
* 3，只要onInterceptTouchEvent返回false，后面的每个事件都会继续分发到touch target执行target's onTouchEvent()
* <li> If you return true from here, you will not receive any
* following events: the target view will receive the same event but
* with the action {@link MotionEvent#ACTION_CANCEL}, and all further
* events will be delivered to your onTouchEvent() method and no longer
* appear here.
* 4，onInterceptTouchEvent返回true, 交给这个ViewGroup的onTouchEvent处理。
* </ol>
*
* @param ev The motion event being dispatched down the hierarchy.
* @return Return true to steal motion events from the children and have
* them dispatched to this ViewGroup through onTouchEvent().
* The current target will receive an ACTION_CANCEL event, and no further
* messages will be delivered here.
*/
public boolean onInterceptTouchEvent(MotionEvent ev) {
return false;
}
看到了吧，这个方法算是ViewGroup不同于View特有的一个事件派发调运方法。在源码中可以看到这个方法实现很简单，但是有一堆注释。其实上面分析了，如果ViewGroup的onInterceptTouchEvent返回false就不阻止事件继续传递派发，否则阻止传递派发。
如上就是所有ViewGroup关于触摸屏事件的传递机制源码分析。具体总结如下：
1,Android事件派发是先传递到最顶级的ViewGroup，再由ViewGroup递归传递到View的。
2,在ViewGroup中可以通过onInterceptTouchEvent方法对事件传递进行拦截，3,onInterceptTouchEvent方法
1）返回true 代表不允许事件继续向子View传递，则交给这个ViewGroup的onTouchEvent处理
2）返回false 代表不对事件进行拦截，默认返回false，则交给子View的dispatchTouchEvent方法处理
4,事件传递到子view 的 dispatchTouchEvent方法中，通过方法传递到当前View的onTouchEvent方法中：
（1）如果返回true，那么这个事件就会止于该view。
（2）如果返回 false ，那么这个事件会从这个子view 往上传递，而且都是传递到父View的onTouchEvent 来接收。
（3）如果传递到ViewGroup的 onTouchEvent 也返回 false 的话，则继续传递到Activity的onTouchEvent中，如果还是false,则这个事件就会“消失“；事件向上传递到中间的任何onTouchEvent方法中，如果返回true，则事件被消费掉，不会再传递。
时间： 2024-10-10 21:57:35