android viewgroup点击变色,Android ViewGroup事件分发
上篇文章已經(jīng)分析了Android的Touch事件分發(fā)。如果沒看的建議先看一下。Android View的Touch事件分發(fā)。
接下來我們開始寫幾種場(chǎng)景，得出一個(gè)初步的執(zhí)行順序，然后我們按照這個(gè)順序開始分析。
首先我們自定義一個(gè)ViewGroup和一個(gè)View，然后重寫相關(guān)事件進(jìn)行打印:
場(chǎng)景一:正常返回super，TouchView設(shè)置click和onTouchListener事件(onTouch返回false)
TouchViewGroup.png
TouchView.png
布局.png
TouchView設(shè)置事件.png
這時(shí)候我們點(diǎn)擊一下TouchView，觸發(fā)事件:
點(diǎn)擊一下.png
可以看到觸發(fā)的DOWN MOVE UP事件順序都為:
ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEven
只是在UP事件的時(shí)候最后多了一個(gè)click事件。
場(chǎng)景二：在場(chǎng)景一的基礎(chǔ)上取消TouchView的onClick事件
TouchView取消click事件.png
這時(shí)候發(fā)現(xiàn)除了，執(zhí)行的順序變?yōu)榱?#xff1a;
ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEven->ViewGroup.onTouchEven
并且只有DOWN事件，其他事件就沒有了。
場(chǎng)景三:在場(chǎng)景二的基礎(chǔ)上TouchViewGroup的onInterceptTouchEvent里面返回true
這個(gè)時(shí)候就只有DOWN事件，并且順序?yàn)?
ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> ViewGroup.onTouchEvent
接下來我們通過源碼來分析:
首先從ViewGroup的dispatchTouchEvent入手
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//...
boolean handled = false;
//...
//1.取消之前的手勢(shì)
// 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();
}
//2.判斷是否攔截
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) { //DOWN
//父類是否攔截 getParent().requestDisallowInterceptTouchEvent();來改變值
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;
}
//....
//3.0 如果是不取消不攔截為down，并且dispatchTransformedTouchEvent返回為true的時(shí)候會(huì)為 mFirstTouchTarget賦值
// 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;
//3.1 如果不取消并且不攔截的情況下，
if (!canceled && !intercepted) {
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {// 3.2 DOWN的時(shí)候
//...
if (newTouchTarget == null && childrenCount != 0) {
//...
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {//3.3 反序for循環(huán)，為了先拿到上層的view
//...
//3.4 拿到child
final View child = getAndVerifyPreorderedView(preorderedList, children, childIndex);
//...
//3.5 根據(jù)child給newTouchTarget賦值 DOWN的時(shí)候因?yàn)?mFirstTouchTarget==null 所以進(jìn)不去 返回的是null
newTouchTarget = getTouchTarget(child);
}
//...
//3.6. 執(zhí)行操作 是執(zhí)行自己的dispatchTouchEvent還是child的dispatchTouchEvent
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
//...
//3.7 子View如果返回true添加一個(gè)newTouchTarget 并且為mFirstTouchTarget賦值
newTouchTarget = addTouchTarget(child, idBitsToAssign);
//....
}
}
}
}
//...
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {//執(zhí)行自身的dispatchTouchEvent
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {// mFirstTouchTarget已經(jīng)賦值
// 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) {//執(zhí)行完3.7操作的
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;
}
}
return handled;
}
/**
* Cancels and clears all touch targets.
*/
private void cancelAndClearTouchTargets(MotionEvent event) {
if (mFirstTouchTarget != null) {
boolean syntheticEvent = false;
if (event == null) {
final long now = SystemClock.uptimeMillis();
event = MotionEvent.obtain(now, now,
MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
syntheticEvent = true;
}
for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
resetCancelNextUpFlag(target.child);
dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);
}
clearTouchTargets();
if (syntheticEvent) {
event.recycle();
}
}
}
//清楚所有的TouchTarget
/**
* Clears all touch targets.
*/
private void clearTouchTargets() {
TouchTarget target = mFirstTouchTarget;
if (target != null) {
do {
TouchTarget next = target.next;
target.recycle();
target = next;
} while (target != null);
mFirstTouchTarget = null;
}
}
//根據(jù)childVie得到TouchTarget
/**
* Gets the touch target for specified child view.
* Returns null if not found.
*/
private TouchTarget getTouchTarget(@NonNull View child) {
// DOWN的時(shí)候因?yàn)?mFirstTouchTarget==null 所以進(jìn)不去 返回的是null
for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
if (target.child == child) {
return target;
}
}
return null;
}
/**
* Transforms a motion event into the coordinate space of a particular child view,
* filters out irrelevant pointer ids, and overrides its action if necessary.
* If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
*/
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
//偽代碼
final boolean handled;
if (child == null) {//執(zhí)行View.dispatchTouchEvent 也就是自己的dispatchTouchEvent
handled = super.dispatchTouchEvent(event);
} else {//執(zhí)行child的dispatchTouchEvent
handled = child.dispatchTouchEvent(event);
}
return handled;
}
//添加TouchTarget 并且給mFirstTouchTarget賦值
/**
* Adds a touch target for specified child to the beginning of the list.
* Assumes the target child is not already present.
*/
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
當(dāng)DOWN的時(shí)候，從注釋和方法名可以看出，會(huì)調(diào)用cancelAndClearTouchTargets,然后在調(diào)用clearTouchTargets使mFirstTouchTarget = null用來廢棄上一次的觸摸手勢(shì)。
接著判斷父類需不需要攔截，先通過(mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0來判斷，在這里可以通過getParent().requestDisallowInterceptTouchEvent(boolean disallowIntercept)來改變值，如果上面為判斷為false再通過onInterceptTouchEvent的返回值來確定,這個(gè)函數(shù)默認(rèn)情況下返回false。
檢測(cè)是否為取消事件，如果不是取消、不攔截并且為 DOWN事件的時(shí)候，就會(huì)對(duì)childView一個(gè)反序的for循環(huán)來遍歷，并且執(zhí)行dispatchTransformedTouchEvent操作，這個(gè)操作用來執(zhí)行dispatchTouchEvent,如果childView是null的話將執(zhí)行View.dispatchTouchEvent,也就是自己的dispatchTouchEvent,反之執(zhí)行childView的dispatchTouchEvent，如果執(zhí)行dispatchTransformedTouchEvent返回的值是true那么將會(huì)調(diào)用addTouchTarget()為這個(gè)childView生成一個(gè)TouchTarget并且執(zhí)行mFirstTouchTarget = target將之賦值于mFirstTouchTarget ，然后跳出for循環(huán)遍歷。
判斷操作，首先判斷mFirstTouchTarget是否為null,如果是DOWN事件，不攔截不取消并且dispatchTransformedTouchEvent返回了true，那么將會(huì)不進(jìn)入這個(gè)判斷，如果不是，那么將會(huì)在這執(zhí)行自身的dispatchTouchEvent函數(shù)并且將返回值賦于handled返回。進(jìn)入else語(yǔ)句，在里面將其mFirstTouchTarget進(jìn)行next遍歷,里面的if語(yǔ)句則是DOWN事件下的dispatchTransformedTouchEvent返回true的情況，直接將其賦值，然后返回，里面的else語(yǔ)句則是，調(diào)用dispatchTransformedTouchEvent,然后將其返回值返回。
到這里，ViewGroups事件分發(fā)源碼的流程就分析了，我們根據(jù)這個(gè)來說說上面的場(chǎng)景。
場(chǎng)景一：我們?cè)赥ouchViewGroup的dispatchTouchEvent正常返回super,DOWN事件先觸發(fā)TouchViewGroup的dispatchTouchEvent，然后就執(zhí)行onInterceptTouchEvent是否攔截，onInterceptTouchEvent返回的是super，也就是false,所以就會(huì)通過dispatchTransformedTouchEvent來執(zhí)行TouchView的dispatchTouchEvent，后面就是View的Touch事件分發(fā)了，View流程將會(huì)按照dispatchTouchEvent->onTouchListener - > onTouchEvent的順序執(zhí)行，因?yàn)樵O(shè)置了點(diǎn)擊事件，所以在這里就返回了true,這個(gè)時(shí)候就會(huì)通過addTouchTarget()給mFirstTouchTarget賦值，下面就直接返回了true。然后在MOVE和UP事件的時(shí)候，也是首先執(zhí)行dispatchTouchEvent，調(diào)用super然后調(diào)用onInterceptTouchEvent詢問是否攔截，還是false,但是這里因?yàn)椴皇荄OWN事件，所以就不會(huì)進(jìn)入判斷對(duì)其childView反遍歷，因?yàn)樵贒OWN的時(shí)候mFirstTouchTarget賦值了，所以這時(shí)候進(jìn)入第4步的else語(yǔ)句里面，這時(shí)候就對(duì)其遍歷執(zhí)行dispatchTransformedTouchEvent，也就是dispatchTouchEvent，然后將其返回。
場(chǎng)景2:我們?nèi)∠它c(diǎn)擊事件，那么在DOWN的時(shí)候就不會(huì)給mFirstTouchTarget賦值，這個(gè)時(shí)候?qū)?huì)進(jìn)入第4步的if判斷里面，直接調(diào)用dispatchTransformedTouchEvent,所以事件就不會(huì)有攔截，最終返回false，所以后續(xù)將不會(huì)接受到任何事件
場(chǎng)景3:我們?cè)赥ouchViewGroup的時(shí)候是在onInterceptTouchEvent返回true，所以我們intercepted=true，這時(shí)候就不會(huì)給mFirstTouchTarget賦值，這個(gè)時(shí)候就調(diào)用自身的dispatchTransformedTouchEvent，同樣的返回false，后續(xù)將不會(huì)接受到事件。
通過源碼的角度我們也知道了為什么會(huì)這么執(zhí)行，初步有點(diǎn)模糊，我們需要通過項(xiàng)目慢慢的來完善對(duì)它的認(rèn)知。希望對(duì)大家有所幫助。
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