很多人都是學(xué)了忘交掏，忘了學(xué)，感覺(jué)永遠(yuǎn)也記不住刃鳄。View 事件分發(fā)到底應(yīng)該怎么學(xué)盅弛？
其實(shí)很簡(jiǎn)單：
1、敲代碼
2叔锐、學(xué)習(xí)原理
3挪鹏、畫(huà)流程圖
View 事件分發(fā) 其實(shí)就4?部分組成
1、 dispatchTouchEvent(MotionEvent ev)
2愉烙、 onInterceptTouchEvent(MotionEvent ev)
3叠纹、 onTouchEvent(MotionEvent ev)
4搭伤、 MotionEvent
那么我們就詳細(xì)的了解一下這四個(gè)的具體含義。
dispatchTouchEvent(MotionEvent ev)
從名字就可以看出這個(gè)方法主要用來(lái)事件的分發(fā)鳞芙，每個(gè) View 都有這個(gè)方法姚建，如果消息能夠傳遞到這個(gè) View，那么這個(gè)方法一定能執(zhí)行。返回 true 代表消耗這個(gè)事件，false 表示不消耗振乏。這個(gè)結(jié)果受兩個(gè)因素的影響。
1秉扑、當(dāng)前 View 的 onTouchEvent() 的返回值慧邮。
2、下級(jí) View dispatchTouchEvent() 方法的返回值
onInterceptTouchEvent(MotionEvent ev)
這個(gè)方法是在dispatchTouchEvent() 中調(diào)用舟陆，误澳，事件攔截，這個(gè)只有在 ViewGroup 才有方法秦躯，View 是沒(méi)有的忆谓。如果當(dāng)前 View 攔截了這個(gè)事件，那么在一個(gè)事件序列中這個(gè)方法不會(huì)被再次調(diào)用了踱承。直到這個(gè)事件序列結(jié)束倡缠。返回的結(jié)果表示是否消耗了這個(gè)事件。
onTouchEvent(MotionEvent ev)
這個(gè)方法是在dispatchTouchEvent() 中調(diào)用勾扭，用來(lái)處理點(diǎn)擊事件毡琉，返回結(jié)果表示是否消耗了這個(gè)事件铁瞒。如果不消耗妙色，返回 false 那么在同一系列事件中，將不會(huì)再給這個(gè)事件派發(fā)慧耍，也就是再次收到事件身辨。
在藝術(shù)探索一書(shū)中有這么一段偽代碼
public boolean dispatchTouchEvent(MotionEvent ev){
boolean consume = false;
if(onInterceptTouchEvent(ev)){
consume = onTouchEvent(ev);
}else{
consume = child.dispatchTouchEvent(ev);
}
return consume;
}
我們可以通過(guò)記憶這一段簡(jiǎn)單的偽代碼，理解整個(gè) View 的事件分發(fā)芍碧。
1煌珊、一個(gè)事件序列
事件序列
2、事件分發(fā)順序
事件分發(fā)順序
事件分發(fā)流程
通過(guò)偽代碼和圖示我們大概了解了 View 的事件分發(fā)泌豆，但是更具體的還需要源碼去分析定庵。
我們便從 Activity 到 View 一起來(lái)走一遍，看看具體代碼是怎么實(shí)現(xiàn)的踪危，里面有什么細(xì)節(jié)給我們解惑的蔬浙。
1、Activity
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
我們結(jié)合上圖和源碼贞远，可以看到很簡(jiǎn)單的幾段代碼畴博，事件分發(fā)調(diào)用的是 Windowd 的superDispatchTouchEvent 分發(fā)。接著往下看蓝仲。
我們知道 Window 是個(gè)抽象類(lèi)俱病，所以用實(shí)現(xiàn)類(lèi) PhoneWindow官疲。
mWindow = new PhoneWindow(this, window, activityConfigCallback);
PhoneWindow 又托管給 DecorView ，就是我們說(shuō)的 RootView 或者 RootViewGroup亮隙。
mDecor = (DecorView) preservedWindow.getDecorView();
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
其實(shí)就是 ViewGroup 的dispatchTouchEvent 方法途凫。
public boolean dispatchTouchEvent(MotionEvent ev) {
······
//從這里開(kāi)始 默認(rèn) handled 為 false 表示不消耗
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
//當(dāng)事件 是 按下的時(shí)候 也是這一事件系列的開(kāi)始
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.
// mFirstTouchTarget = null;重置mFirstTouchTarget 和 FLAG_DISALLOW_INTERCEPT
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// 表示是否攔截
final boolean intercepted;
//當(dāng)事件類(lèi)型為 ACTION_DOWN 或者 mFirstTouchTarget 不為空的時(shí)候
//什么是 mFirstTouchTarget ？整體分析可知 當(dāng)這個(gè)事件被子 view 消耗的時(shí)候咱揍，
//mFirstTouchTarget 會(huì)指向這個(gè) view颖榜，也就是第一個(gè)消耗這個(gè)事件的 view。
//當(dāng) ViewGroup 不攔截的時(shí)候且子 view消耗了這個(gè)事件 那么mFirstTouchTarget 煤裙！=null掩完。
//那么 當(dāng)事件類(lèi)型為 MOVE 或者 UP 的時(shí)候，如果 mFirstTouchTarget 硼砰！=null 那就說(shuō)明
//有 view 消耗這個(gè)事件了且蓬，該系列的事件都默認(rèn)交給它處理
//也就是事件的開(kāi)始 和 事件有消耗后 都會(huì)走這個(gè)方法。當(dāng)然也不是絕對(duì)的
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//FLAG_DISALLOW_INTERCEPT這個(gè)參數(shù)是子 view 通過(guò)requestDisallowInterceptTouchEvent 方法题翰，改變這個(gè)值 恶阴，來(lái)控制 父 view 是否攔截
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
//當(dāng)需要攔截的時(shí)候 那就走自己的onInterceptTouchEvent 方法具體自己實(shí)現(xiàn) ，不需要那就intercepted 為 false
//需要注意的是 對(duì)于 DOWN 子 view 通過(guò) requestDisallowInterceptTouchEvent 方法是控制不了父 view 的攔截方法的豹障，因?yàn)楫?dāng)有 DOWN 事件的時(shí)候 就會(huì)觸發(fā) 之前的重置方法冯事。
//所以只能針對(duì) MOVE UP 等，可以讓 父 view 不在攔截事件血公，可以使父 view 開(kāi)始攔截事件
//正是因?yàn)?FLAG_DISALLOW_INTERCEPT 昵仅，如果我們父 view 開(kāi)始攔截，并消耗了這個(gè)事件累魔，那么 mFirstTouchTarget摔笤！=null 就不會(huì)成立，因?yàn)閂iewGroup 的子 view 成功消耗這個(gè)事件后 才會(huì)mFirstTouchTarget垦写！=null吕世。所以以后的事件也就不會(huì)再走 onInterceptTouchEvent，直接返回 intercepted = true 梯投。
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;
//當(dāng)ViewGroup不攔截時(shí)命辖，這里對(duì) ViewGroup 的子 view 進(jìn)行處理
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 = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
//遍歷子 view
for (int i = childrenCount - 1; i >= 0; i--) {
//這一堆的代碼有點(diǎn)復(fù)雜 不過(guò)就一個(gè)目的 當(dāng)前子 view 是都能接受點(diǎn)擊事件
//如何判斷呢？ 1分蓖、是否在播放動(dòng)畫(huà) 2尔艇、點(diǎn)擊的坐標(biāo)是否在該子 view 的區(qū)域
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;
}
//這就是判斷是否可以點(diǎn)擊的方法之一 view 要顯示，是否在播放動(dòng)畫(huà)
/**
* Returns true if a child view can receive pointer events.
* @hide
* private static boolean canViewReceivePointerEvents(@NonNull View child) {
* return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
* || child.getAnimation() != null;
* }
*/
//判斷二 是否在子 view 的范圍
/**
* protected boolean isTransformedTouchPointInView(float x, float y, View child,
PointF outLocalPoint) {
final float[] point = getTempPoint();
point[0] = x;
point[1] = y;
transformPointToViewLocal(point, child);
final boolean isInView = child.pointInView(point[0], point[1]);
if (isInView && outLocalPoint != null) {
outLocalPoint.set(point[0], point[1]);
}
return isInView;
}
*
*/
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//mFirstTouchTarget 是一個(gè)鏈表形式 遍歷這個(gè)鏈表 如果有這個(gè) view 那么就直接賦值 newTouchTarget
//注意 mFirstTouchTarget 是在View 的子 view中賦值的
// 說(shuō)明點(diǎn)擊確實(shí)在子 view 的區(qū)域 直接返回不用再繼續(xù)遍歷了
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);
//實(shí)際是 調(diào)用 子 view 的 dispatchTouchEvent 方法咆疗。依次遞歸下去
//如果 子 view dispatchTouchEvent 返回true 那么 newTouchTarget = addTouchTarget(child, idBitsToAssign);
// newTouchTarget 被賦值并跳出循環(huán) 其實(shí)是 mFirstTouchTarget鏈表添加數(shù)據(jù)
alreadyDispatchedToNewTouchTarget = true;
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();
}
//當(dāng) newTouchTarget 還是null 那就 鏈表 最后一個(gè) 賦值給newTouchTarget
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.
//當(dāng) mFirstTouchTarget 為空 其實(shí)也就是子 view 為空漓帚，調(diào)用 view 的 dispatchTouchEvent 方法
//就是 viewGroup 如果需要消耗事件 其實(shí)調(diào)用的是 view 的方法
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.
//更新重置 狀態(tài)
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);
}
//最后返回 消耗的情況
return handled;
}
我們來(lái)看下 ViewGroup 的分發(fā)。
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);
//當(dāng)沒(méi)有子 view 那么它就相當(dāng)于 view 調(diào)用 view 的方法午磁。
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
//如果有 那么就 遞歸這個(gè)方法了
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()) {
//當(dāng)沒(méi)有子 view 那么它就相當(dāng)于 view 調(diào)用 view 的方法尝抖。
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) {
//當(dāng)沒(méi)有子 view 那么它就相當(dāng)于 view 調(diào)用 view 的方法毡们。
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;
}
其實(shí)我們發(fā)現(xiàn)這一切都和 mFirstTouchTarget 有關(guān)系，當(dāng) viewGroup 需要自己消耗事件的時(shí)候昧辽，那么 mFirstTouchTarget 肯定是 null衙熔，也就是子 view 不消耗，或者自己攔截搅荞，都會(huì)造成 mFirstTouchTarget ==null红氯，那么當(dāng)調(diào)用 dispatchTransformedTouchEvent 方法是，就會(huì)觸發(fā) view 的 onTouchEvent 方法咕痛，viewGroup 自己去處理事件痢甘。
首先我們看看 View 的 dispatchTouchEvent() 方法（只保留了我們需要的源碼）。
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);
}
//這里是開(kāi)始
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;
//判斷是否有監(jiān)聽(tīng)事件 并且 mOnTouchListener不為空
//view 的 enabled 為true 并且onTouch方法也返回true
//那么直接返回 true
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//當(dāng) onTouch 被調(diào)動(dòng) 且返回true 那么onTouchEvent不會(huì)調(diào)用了
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;
}
我們會(huì)發(fā)現(xiàn) View 可以調(diào)用 onTouch() 且返回 true, onTouchEvent就不會(huì)再調(diào)用了茉贡，這就是一個(gè)優(yōu)先級(jí)的問(wèn)題了塞栅。
最后是 onTouchEvent 方法
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
//是否可點(diǎn)擊
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
//就算 不可用的情況下 也可能會(huì)消耗點(diǎn)擊事件 只要 clickable 為true
if ((viewFlags & ENABLED_MASK) == DISABLED) {
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;
}
//如果 view 有代理會(huì)做這個(gè)方法 具體不說(shuō)了
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
//只要控件的clickable 或者 long_clickable 或者 CONTEXT_CLICKABLE 有一個(gè)為 true
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
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
//這是 up 所以 長(zhǎng)按事件回調(diào)移除
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.
// 我們?cè)O(shè)置點(diǎn)擊事件 是在這兒 開(kāi)始的~~看好了 我們發(fā)現(xiàn)是通過(guò) post 把 run 里的調(diào)用 performClick() 方法。用 Runnable 腔丧，通過(guò) post 形式執(zhí)行 performClick放椰，而不是直接調(diào)用 performClick ， 因?yàn)檫@可以讓這個(gè) view 更新的視覺(jué)狀態(tài)在這個(gè)方法執(zhí)行之前愉粤。
//這個(gè)比如當(dāng)這個(gè) view 繪制 顯示 完成之后 才可以 點(diǎn)擊 之類(lèi)的 等等
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:
if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
}
mHasPerformedLongPress = false;
if (!clickable) {
checkForLongClick(0, x, y);
break;
}
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, x, y);
}
break;
case MotionEvent.ACTION_CANCEL:
if (clickable) {
setPressed(false);
}
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
break;
case MotionEvent.ACTION_MOVE:
if (clickable) {
drawableHotspotChanged(x, y);
}
// Be lenient about moving outside of buttons
if (!pointInView(x, y, mTouchSlop)) {
// Outside button
// Remove any future long press/tap checks
removeTapCallback();
removeLongPressCallback();
if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
}
break;
}
//當(dāng) clickable 為 true 那么一定返回 true 不管執(zhí)行了 點(diǎn)擊事件啥 或者 其他 這個(gè)事件在這兒一定會(huì)消耗
//就是返回 true 所以當(dāng)設(shè)置 不可點(diǎn)擊的時(shí)候且clickable 為false 才會(huì)不消耗這個(gè)事件
return true;
}
return false;
}
超級(jí)會(huì)員：mOnTouchListener
會(huì)員：onTouchEvent
普通用戶(hù)：setOnClickListener
最后根據(jù)上面的源碼分析后砾医，我們整理一些結(jié)論，結(jié)合結(jié)論和源碼分析衣厘，我們更好的理解 View的事件分發(fā)如蚜。（copy from 《藝術(shù)探索》 + 自己的理解）
1、同一個(gè)事件序列是從手指觸摸屏幕的那一刻開(kāi)始头滔，直到手指離開(kāi)屏幕的那一刻結(jié)束怖亭，在這個(gè)過(guò)程產(chǎn)生的一系列事件涎显，是從 down 開(kāi)始 經(jīng)過(guò) n 個(gè) move 最后 up 結(jié)束坤检。
2、正常情況下期吓，一個(gè)事件只能被一個(gè) View 攔截且消耗早歇，原因參考 3。一旦一個(gè) View 攔截了某事件讨勤，那么這個(gè)事件序列內(nèi)的所有事物都會(huì)直接交給它處理箭跳，因此同一個(gè)事件序列中的事件不能由兩個(gè) view 同時(shí)處理，注意是同時(shí)潭千，但是通過(guò)特殊手段可是谱姓，比如將一個(gè)View 的事件強(qiáng)行傳遞給其他view，這是無(wú)賴(lài)操作刨晴。
3屉来、某個(gè) View 一旦決定攔截路翻，那么這個(gè)事件序列只能由他來(lái)出來(lái)，如果事件能傳遞給他茄靠，而且他的 onInterceptTouchEvent 不會(huì)再繼續(xù)調(diào)用茂契，因?yàn)?View 攔截那么mFirstTouchTarget 就不會(huì)在 子 View 中賦值，mFirstTouchTarget ==null 直接返回 true 慨绳，最后走 View 的 ouTouchEvent 方法掉冶。
4、某個(gè) View 一旦開(kāi)始處理事件脐雪，如果它不消耗 ACTION_DOWN 事件（ onTouchEvent 返回 false）厌小，那么同一序列的而其他事件都不會(huì)交給他處理，而是將事件重新交給他的父元素處理战秋，即 父 View 的 onTouchEvent 會(huì)調(diào)用 召锈。源碼上其實(shí)就是 比如子 View onTouchEvent 返回 false，因?yàn)?dispatchTouchEvent 是 遞歸的获询，所以返回 子 view 的dispatchTouchEvent 返回 false涨岁，最后 mFirstTouchTarget 還是null ，所以 父 view（ViewGroup） 調(diào)用 View 的 dispatchTouchEvent 進(jìn)行處理吉嚣，最后父 View調(diào)用onTouchEvent 方法梢薪，來(lái)處理這個(gè)事件。
5尝哆、如果 View 不消耗 ACTION_DOWN 以外的其他事件秉撇，那么這個(gè)點(diǎn)擊事件就會(huì)消失，此時(shí)的父元素的 onTouchEvent 不會(huì)調(diào)用秋泄，而且當(dāng)前 View 可以持續(xù)收到后續(xù)的事件琐馆，最終這些消失的事件會(huì)交給 Activity 處理。
6恒序、ViewGroup 默認(rèn)不攔截任何事件瘦麸，即 onInterceptTouchEvent 返回 false。
7歧胁、View 沒(méi)有 onInterceptTouchEvent滋饲。事件傳遞給它，ouTouchEvenr 就會(huì)調(diào)用喊巍。
8屠缭、View 的 ouTouchEvent 會(huì)默認(rèn)消耗事件 返回true。除非他是不可點(diǎn)擊 clickable 和longclickable 同時(shí)是 false崭参。longclickable默認(rèn)為false呵曹，button 默認(rèn) clickable 是true，textview 默認(rèn) false。
9奄喂、View 的enable 屬性不影響 ouTouchEvent 的返回值之剧，只要longclickable 或 clickable 有一個(gè)是 true ，那么ouTouchEvent 就返回 true砍聊。
10背稼、onClick 會(huì)發(fā)生的前提是 view 可點(diǎn)擊。并過(guò)去收到了down 和up玻蝌。
11蟹肘、事件傳遞是從外向內(nèi)的，事件總是先傳遞給父view俯树，然后再有父view分發(fā)給子view帘腹，通過(guò) requestDisallowInterceptTouchEvent 方法，子類(lèi)可以干預(yù)父 View 的事件分發(fā)過(guò)程许饿。ACTION_DOWN 除外阳欲。
12、mOnTouchListener > onTouchEvent > setOnClickListener
參考 《Android開(kāi)發(fā)藝術(shù)探索》
