} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
}
return handled;
}
首先看下注释１处的mFirstTouchTarget，那么mFirstTouchTarget != null是什么意思呢？这个从后面的代码逻辑可以看出来，当事件由ViewGroup的子元素成功处理时，mFirstTouchTarget会被赋值并指向子元素。
也就是说，当ViewGroup不拦截事件并将事件交由子元素处理时mFirstTouchTarget才不为null。反之，一旦事件由当前ViewGroup拦截时，mFirstTouchTarget就是null，这样当ACTION_MOVE和ACTION_UP事件到来时，由于mFirstTouchTarget是null，将导致执行注释2处代码，ViewGroup的onInterceptTouchEvent不会再被调用，并且同一序列中的其他事件都会默认交给它处理。
当然，这里有一种特殊情况，就是上述注释3处的FLAG_DISALLOW_INTERCEPT标记位，这个标记位是通过ViewGroup的requestDisallowInterceptTouchEvent方法来设置的，一般用于子View中。FLAG_DISALLOW_INTERCEPT一旦设置后，ViewGroup将无法拦截除了ACTION_DOWN以外的其他点击事件。为什么说是除了ACTION_DOWN以外的其他事件呢？这是因为ViewGroup在分发事件时，如果是ACTION_DOWN就会重置FLAG_DISALLOW_INTERCEPT这个标记位，具体代码是执行注释5处代码，将导致子View中设置的这个标记位无效。因此，当面对ACTION_DOWN事件时，ViewGroup总是会调用自己的onInterceptTouchEvent方法来询问自己是否要拦截事件，也就是一定会执行注释4，。因此子View调用requestDisallowInterceptTouchEvent方法并不能影响ViewGroup对ACTION_DOWN事件的处理，所以FLAG_DISALLOW_INTERCEPT就是为了不拦截后续的非ACTION_DOWN事件设计的。
如果ViewGroup决定拦截ACTION_DOWN事件，就会执行注释6处的dispatchTransformedTouchEvent方法，暂时先不管dispatchTransformedTouchEvent内部，下面统一分析，mFirstTouchTarget就是null，后续的非ACTION_DOWN事件将会默认交给它处理并且不再调用它的onInterceptTouchEvent方法
如果ViewGroup不拦截事件的时候，事件会向下分发交由它的子View进行处理，具体执行注释7处，然后在注释8处，遍历ViewGroup的所有子元素，然后判断子元素是否能够接收到点击事件。是否能够接收点击事件主要由两点来衡量：子元素是否在播动画和点击事件的坐标是否落在子元素的区域内。如果某个子元素满足这两个条件，那么事件就会传递给它来处理，然后也会调用到dispatchTransformedTouchEvent方法，暂时先不管dispatchTransformedTouchEvent内部，下面统一分析，如果dispatchTransformedTouchEvent返回了true，就会执行注释10处，调用addTouchTarget()方法，内部会完成mFirstTouchTarget的赋值，并且在注释11处终止对子元素的遍历，那我们就看下addTouchTarget()的源码，源码如下，路径android.view.ViewGroup#addTouchTarget
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;// 单链表结构
mFirstTouchTarget = target;// 这里就会完成mFirstTouchTarget的赋值
return target;
}
mFirstTouchTarget是否被赋值，将直接影响到ViewGroup对事件的拦截策略，如果mFirstTouchTarget为null，那么ViewGroup就默认拦截接下来同一序列中所有的点击事件，这一点在前面已经做了分析。
如果遍历所有的子元素后事件都没有被合适地处理，这包含两种情况：第一种是ViewGroup没有子元素；第二种是子元素处理了点击事件，但是在dispatchTouchEvent中返回了false，这一般是因为子元素在onTouchEvent中返回了false。在这两种情况下，ViewGroup会自己处理点击事件，同样也会调用到注释6处代码执行dispatchTransformedTouchEvent方法，就如同ViewGroup自己拦截了事件，自己来处理。
上面提到ViewGroup自身拦截或子View没有处理，还是需要ViewGroup自身处理，都会调用dispatchTransformedTouchEvent()，传入的参数child为null，如果是没拦截，遍历到了子View，也会调用dispatchTransformedTouchEvent()，传入的参数child就是遍历出来的子View本身，因此下面看下dispatchTransformedTouchEvent()，源码如下，路径android.view.ViewGroup#dispatchTransformedTouchEvent
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// Canceling motions is a special case. We don’t need to perform any transformations
// or filtering. The important part is the action, not the contents.
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
// Calculate the number of pointers to deliver.
final int oldPointerIdBits = event.getPointerIdBits();
final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
// If for some reason we ended up in an inconsistent state where it looks like we
// might produce a motion event with no pointers in it, then drop the event.
if (newPointerIdBits == 0) {
return false;
}
// If the number of pointers is the same and we don’t need to perform any fancy
// irreversible transformations, then we can reuse the motion event for this
// dispatch as long as we are careful to revert any changes we make.
// Otherwise we need to make a copy.
final MotionEvent transformedEvent;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
event.offsetLocation(offsetX, offsetY);
handled = child.dispatchTouchEvent(event);
event.offsetLocation(-offsetX, -offsetY);
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
// Perform any necessary transformations and dispatch.
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
transformedEvent.offsetLocation(offsetX, offsetY);
if (! child.hasIdentityMatrix()) {
transformedEvent.transform(child.getInverseMatrix());
}
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
提取核心代码可以看到主要执行了
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
handled = child.dispatchTouchEvent(transformedEvent);
}
return handled;
也就是说如果传入的child为null，会return super.dispatchTouchEvent()，也就是会调用ViewGroup的父类View的dispatchTouchEvent()，这样点击事件开始交由View来处理；如果child不为null，就调用子view本身的dispatchTouchEvent()，如果子View不是ViewGroup，则也会交由View的dispatchTouchEvent()处理这个事件，如果子View是ViewGroup，那就开启新一轮的事件分发，就又回到了上面分析的ViewGroup的dispatchTouchEvent()方法
然后事件到了View的dispatchTouchEvent (MotionEvent event)，直接上源码如下，路径android.view.View#dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent event) {
// If the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
// We don’t have focus or no virtual descendant has it, do not handle the event.
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// We have focus and got the event, then use normal event dispatch.
event.setTargetAccessibilityFocus(false);
}
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.monTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {// 1判断有mOnTouchListener并且mOnTouchListener返回true
result = true;
}
if (!result && onTouchEvent(event)) {// 2如果上述result就不会执行onTouchEvent(event)
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn’t want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
从代码可以看出View对点击事件的处理过程就比较简单了，因为View（这里不包含ViewGroup）是一个单独的元素，它没有子元素因此无法向下传递事件，所以它只能自己处理事件。注释１处，可以看出View对点击事件的处理过程，首先会判断有没有设置OnTouchListener，如果OnTouchListener中的onTouch方法返回true，那么onTouchEvent就不会被调用，可见OnTouchListener的优先级高于onTouchEvent，这样做的好处是方便在外界处理点击事件。如果没设置OnTouchListener，就会执行View的onTouchEvent(MotionEvent event)方法，代码精简如下，源码路径android.view.View#onTouchEvent
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;// 1判断View是否可点击，包括点击或长按事件
if ((viewFlags & ENABLED_MASK) == DISABLED) {// 2View处于DISABLED状态
if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
// A disabled view that is clickable still consumes the touch
// events, it just doesn’t respond to them.
return clickable;
}
if (mTouchDelegate != null) {//如果设置了TouchDelegate这里会执行TouchDelegate的onTouchEvent，类似TouchEventListener
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {//3clickable
switch (action) {
case MotionEvent.ACTION_UP:
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
if ((viewFlags & TOOLTIP) == TOOLTIP) {
handleTooltipUp();
}
if (!clickable) {
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
}
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
// take focus if we don’t have it already and we should in
// touch mode.
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
if (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
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ent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
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