艺术开发-事件分发
2016-08-09 本文已影响51人
路途等待
(1)同一个事件序列是从手指接触屏幕的那一刻开始的,到手指离开屏幕的那一刻结束.这个事件序列从Down事件开始中间含有数量不定的Move事件,最终以Up事件结束
(2) 正常情况下,一个时间序列只能被一个View拦截且消耗,因为一旦一个元素拦截了某个事件,那么同一个时间序列内的所有事件都会直接交给他处理,因此同一个事件序列内的事件不能分别有两个View同时处理,但是通过其他手段,比如把一个View的本该自己处理的事件通过onTouchEvent强行传递给其他View处理
(3)某个view如果决定拦截,那么这个事件序列都只能由他来处理(前提是这个事件序列能够传递给他),并且他的onInterceptTouchEvent(ev)不会被调用
(2)(3)解释:
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
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;
}
-
上面一段代码是从ViewGroup中的dispatchTouchEvent()方法中得到的,Down事件容易理解, mFirstTouchTarget != null解释一下,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,就是说,如果是ViewGroup消费了事件,那么他的Down事件到来的时候肯定会调用onInterceptTouchEvent(ev)方法,判断是否拦截,当后续的Up和Move事件到来的时候因为mFirstTouchTarget != null为false,所以onInterceptTouchEvent(ev)就不会调用了.
-
如果ViewGroup没有消费事件而是子元素消费了事件,那么mFirstTouchTarget != null就为true了,因为final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;默认为false表示不拦截事件,所以onInterceptTouchEvent(ev);将会被会被调用
(4)某个View一旦开始处理事件,如果他不消耗Down事件(也就是说他的onTouchEvent返回了false),那么同一事件中的其他事件都不会交给他来处理.并且事件将重新交给他的父元素处理,也就是说这个时候他的父元素的onTouchEvent将会被调用.通俗一点说就是事件一旦交给一个View处理,那么他就必须消耗掉,否则同一事件序列中剩下的其他事件就不再交给他来处理。
(4)解释:
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;
}
- 这个事ViewGroup中的dispatchTouchEvent()方法中的一段代码,其中dispatchTransformedTouchEvent()方法内部就是调用子元素的dispatchTransformedTouchEvent();方法,如果子元素在Down事件中没有消费,就会返回false,因为这个方法是在for循环中进行的,就会遍历下面的view,如果返回的是true,就会跳出循环
(5)如果View不消耗除Down事件以外的其他事件,那么这个点击事件会消失,此时父元素的onTouchEvent不会被调用,并且当前View可以持续收到后续的事件,最终这些消失的点击事件都会传递给Activity处理
(6)ViewGroup默认不拦截任何事件.android源码中的ViewGroup的onInterceptTouchEvent(ev)默认返回false
(7)View没有onInterceptTouchEvent(ev)方法, 一旦有点击事件传递给他,那么他的onTuchEvent方法就会被调用
(8)View的onTouchEvent默认都会消耗事件(也就是说返回true),除非他是不可点击的(也就是说他的aclickable和longClickable同时为false).View的longClickable属性默认都为false,clickable属性要分情况,比如Button的clickable属性默认为true,而TextView的clickable属性默认为false.
(9)View的enable属性不影响onTouchEvent的默认返回值.哪怕iew是disable状态
(10)onClick会发生的前提是当前View是可点击的,并且他收到了down和up事件
(11)事件的传递过程是有外向内的,即事件总是先传给父元素,然后在由父元素分发给子View,通过 requestDisallowInterceptTouchEvent()可以在子元素中干预父元素的分发过程,但是Down事件除外,因为父元素在Down事件来的时候会初始化requestDisallowInterceptTouchEvent()这个方法的东西,和面会解释
(8)(9)(10)解释:
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
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
// performClick directly. This lets other visual state
// of the view update before click actions start.
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClick();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
mHasPerformedLongPress = false;
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0);
}
break;
case MotionEvent.ACTION_CANCEL:
setPressed(false);
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_MOVE:
drawableHotspotChanged(x, y);
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
removeTapCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
// Remove any future long press/tap checks
removeLongPressCallback();
setPressed(false);
}
}
break;
}
return true;
}
return false;
}
</pre>
上面的是View的onTouchEvent方法,里面内容比较多我们单抽出来讲
<pre>
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
......
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClick();
}
}
}
}
break;
}
return true;
}
return false;
}
- 上面是精简版的View的onTouchEvent方法,我们把一些英文注释删了,反正也看不懂,还有Down Move Cancel三个事件删了,因为这个几个事件对整个分发没有起到任何影响,同时还影响我们代码的可读性.从上面的代码中我们看到上面蓝色的部分是一个if包裹的,如果满足了这个if条件就会返回true,从上面的代码中可以看到只要View的Clickable和longClickable有一个为true,那他就会消耗这个事件,也就是说onTouchEvent方法返回true.这里面还有一个很重要的方法就是performClick()方法,当Up事件发生时,就会调用这个方法,其实他内部调用的就是我们的额onClick方法,前提是我们设置了onClickListener.我们看下他 的源码
public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
return result;
}
</pre>
- View的longClickable属性默认都为false,clickable属性要分情况,比如Button的clickable属性默认为true,而TextView的clickable属性默认为false.但是我们通过setOnLongClickable和setOnClickable可以分别改变View的Clickable和Long_Clickable属性通过setOnLongClickListener和setOnClickListeren会自动把View的Long_Clickabel和View的Clickable属性设置为true,这一点可以通过源码来解释
<pre>
public void setOnClickListener(@Nullable OnClickListener l) {
if (!isClickable()) {
setClickable(true);
}
getListenerInfo().mOnClickListener = l;
}
public void setOnLongClickListener(@Nullable OnLongClickListener l) {
if (!isLongClickable()) {
setLongClickable(true);
}
getListenerInfo().mOnLongClickListener = l;
}
- 到这里我们基本上把事件分发给解释的差不多了,下面我们通过源码系统的走一边这个过程,我先用文字的形式走一下
首先事件会到达顶级的View这个View一般是ViewGroup,这个时候会调用ViewGroup的dispatchTouchEvent()方法,在这个方法里面会调用onInterceptTouchEvent(ev);方法,如果这个方法返回true,那么事件就会由ViewGroup处理,这个时候如果ViewGroup的mOnTouchListener被设置则onTouch方法会被调用,否则,onTouchEvent方法被调用,也就是说如果mOnTouchListener被提供的话onTouch会屏蔽掉onTouchEvent方法(这个我稍后会借助源码进行分析)在onTouchEvent方法中如果设置了mOnClickListener.,则onClick()方法会被调用. 如果顶级的ViewGroup不拦截事件,那么事件就会传给他的子view,这个时候子View的dispatchTouchEvent()方法会被调用,如果子View的mOnTouchListener被设置则onTouch方法会被调用,这个时候怎么处理还要看OnTouch的返回值,如果返回false当前的onTouchEvent方法被调用,如果返回true当前的onTouchEvent不会被调用,在onTouchEvent方法中,如果子View设置了OnClicalistener,那么他的onClick方法会被调用.当Move事件来的时候还会先走ViewGroup的dispatchTouchEvent(),重新进入分发.
现在我们结合源码来分析一下
@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;
// 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.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
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 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.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
// 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) {
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();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
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);
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;
}
</pre>
上面的是整个ViewGroup的dispatchTouchEvent()方法,比较长,我们分段来说
<pre>
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
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;
}
- 这段代码解释的就是,ViewGroup在如下两种情况下会判断是不是要拦截当前事件:第一个条件是这个事件是Down事件,第二个条件是mFirstTouchTarget != null,Down事件比较容易理解,mFirstTouchTarget != null在什么时候不为null呢?通过分析后面的代码,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,这个时候才不为null,当Down事件来的时候ViewGroup会判断一下是不是要拦截,如果拦截,当Move和Up事件来的时候第一条和第二条都不成立,所以不会在调用onInterceptTouchEvent(ev);方法判断是否要拦截如果ViewGroup不拦截的时候,这个 时候事件会传给子View,mFirstTouchTarget 会被赋值并指向子元素,当Move和Up来的时候,会重新调用ViewGroup的dispatchTouchEvent().这个时候第一条就不成立,不是Down事件了,但是第二条成立了,还会调用onInterceptTouchEvent(ev);判断是否要拦截事件,因为这句话final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;默认返回的是false,我们在上面第11条的时候提到过子View可以通过requestDisallowInterceptTouchEvent()方法改变父View是否要拦截,改变的就是disallowIntercept的值,但是当我们设置了true的时候,ViewGroup将不会拦截除了Down事件以外的事件,因为在上面没有说,这里我们解释一下,看一段源码:
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// 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();
}
- 这段代码要比我们上面分析的代码调用的时间早,在resetTouchState();这个方法中FLAG_DISALLOW_INTERCEPT;这个标记位会被重置,所以在ViewGroup收到Down事件的时候final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;这段代码永远都是false
继续分析,看下面的源码
final int childrenCount = mChildrenCount;
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 = buildOrderedChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
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);
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;
}
- 当ViewGroup不拦截事件的时候,ViewGroup会遍历的子View,然后判断子View是否能接收点击事件,是否能接收点击事件通过两点来判断,第一点是子View是否在播放动画,第二点是点击的坐标是否落在了子View上,如果这两点满足,事件就会给这个子View来处理,dispatchTransformedTouchEvent()注意一下这个方法,这个方法内部就是调用了子View的dispatchTouchEvent()方法,如果子View的dispatchTouchEvent()返回的是true,就会跳出for循环,如果子View的dispatchTouchEvent()返回了false,就将继续遍历下一个子View.这个时候事件就传递给了子View,下面我们分析一下子View的事件
下面这段源码是子View的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)) {
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && 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;
}</pre>
上面的源码有点长,我们精简一下
<pre>
public boolean dispatchTouchEvent(MotionEvent event) {
boolean result = false;
if (onFilterTouchEventForSecurity(event)) {
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
return result;
}
我们删除了一些对我们没有用的东西
通过上面的源码,可以发现子View的事件分发就简单多了,因为子View没有涉及到分发,而是自己处理事件,从源码中可以看出,子View会首先判断有没有设置mOnTouchListener,如果设置了就会调用mOnTouchListener.onTouch();如果onTouch方法返回了true,那么子View的dispatchTouchEvent()方法就直接返回了true,这个时候下面的onTouchEvent(event)方法将不会被调用,如果onTouch返回的是false,那么第一个if不成立,就会走第二个if;就会调用onTouchEvent(event)方法,onTouchEvent我们在上面以经分析过了,基本一样的,这个时候我们的事件分发到此结束.
