點(diǎn)擊事件的傳遞規(guī)則
點(diǎn)擊事件歧焦，說直接一點(diǎn)就是MotionEvent對(duì)象嗤军，事件的傳遞莉御，就是將MotionEvent對(duì)象分發(fā)給不同的View來處理的過程且轨，分發(fā)過程主要由三個(gè)重要方法組成：
public boolean dispatchTouchEvent(MotionEvent event);-
public boolean onInterceptTouchEvent(MotionEvent ev);(只存在于ViewGroup中，默認(rèn)值為false) public boolean onTouchEvent(MotionEvent event);
先簡(jiǎn)單描述一下它們的關(guān)系：
首先魄健，事件會(huì)傳遞給根ViewGroup赋铝，它的dispatch方法被調(diào)用，在dispatch中會(huì)詢問onIntercept來決定該ViewGroup是否消費(fèi)該事件沽瘦，如果返回true革骨，那么該ViewGroup就會(huì)消費(fèi)掉該事件，將event交給當(dāng)前ViewGroup的onTouchEvent來處理析恋，事件結(jié)束良哲。如果onIntercept返回了false，表示當(dāng)前ViewGroup不消費(fèi)事件助隧，會(huì)將它傳遞給他的子元素筑凫。然后子元素的dispatch方法執(zhí)行，一直到事件被處理（onTouchEvent返回值為true）喇颁。單一View沒有onIntercept漏健，dispatchTouchEvent會(huì)直接接收onTouchEvent的返回值，返回true說明事件被當(dāng)前View接收并處理了橘霎。
Activity#DispatchTouchEvent源碼分析
所有的點(diǎn)擊事件都是從Activity開始傳遞的蔫浆，先看一下Activity中，dispatch方法的源碼
/**
* 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);
}
首先姐叁，事件會(huì)傳遞到getWindow().superDispatchTouchEvent(ev)瓦盛，它的返回值決定了是否會(huì)調(diào)用Activity的onTouchEvent(ev)。
我們繼續(xù)看getWindow().superDispatchTouchEvent(ev)的源碼外潜。Window的唯一實(shí)現(xiàn)類就是PhoneWindow(com.android.internal.policy.impl.PhoneWindow)原环，直接查看superDispatchTouchEvent方法：
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
代碼很簡(jiǎn)單，直接調(diào)用了DecorView的superDispatchTouchEvent方法处窥。DecorView是PhoneWindow的內(nèi)部類嘱吗，看一下代碼：
private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {
......
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
.......
看到這里，事件的傳遞流程其實(shí)就已經(jīng)很清楚了：
Activity首先接收到事件，通過一系列的調(diào)用谒麦，最終傳遞到了 DecorView 的 superDispatchTouchEvent俄讹，DecorView繼承自FrameLayout又繼承自ViewGroup，最終調(diào)用的方法實(shí)際上是ViewGroup的dispatchTouchEvent(ev)方法绕德。由ViewGroup來進(jìn)行事件分發(fā)患膛，如果分發(fā)成功，事件被消費(fèi)耻蛇，返回值為true踪蹬。如果分發(fā)失敗，事件仍然沒有被消耗臣咖，返回false跃捣，事件就會(huì)交給Activity#onTouchEvent處理。
我們只需要記住一點(diǎn)：事件傳遞從Activity開始夺蛇，最終會(huì)傳遞到根ViewGroup的dispatchTouchEvent枝缔。如果最終返回值為false，說明事件沒有被攔截蚊惯，最終會(huì)交給Activity的onTouchEvent來處理。
ViewGroup的DispatchTouchEvent源碼分析
源碼很長(zhǎng)灵临，只截取了部分關(guān)鍵代碼如下：
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//標(biāo)記事件是否已經(jīng)被攔截
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
//@ 獲取Action截型，Masked表示不考慮多點(diǎn)觸控
final int actionMasked = action & MotionEvent.ACTION_MASK;
//@ 如果是ACTION_DOWN，清除所有初始狀態(tài)儒溉，主要包括以下動(dòng)作：
// 設(shè)置mFirstTouchTarget值為null
// 清除FLAG_DISALLOW_INTERCEPT標(biāo)志宦焦，如果設(shè)置該標(biāo)志為true，ViewGroup不攔截事件
if (actionMasked == MotionEvent.ACTION_DOWN) {
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// 用于標(biāo)記事件是否被當(dāng)前ViewGroup消費(fèi)
final boolean intercepted;
//以下代碼用來判斷事件是否被當(dāng)前ViewGroup消費(fèi)顿涣，主要流程如下：
//-----------------------------------------------------------
//1.Down事件到來波闹，必定會(huì)進(jìn)入intercepted = onInterceptTouchEvent(ev);
//2.如果ViewGroup決定消費(fèi)事件，那么intercepted被賦值為true
//3.intercepted被賦值為true之后涛碑，下面標(biāo)記###--->1的if代碼塊不再執(zhí)行精堕，直接跳到 ###--->2
//4.mFirstTouchTarget賦值的語句在###--->3標(biāo)記，包含在###--->1的if代碼塊內(nèi)蒲障，所以歹篓，如果當(dāng)前ViewGroup消費(fèi)了事件，mFirstTouchTarget就一定是null
//5.繼續(xù)看###--->2的代碼揉阎，mFirstTouchTarget等于null庄撮，滿足條件，調(diào)用dispatchTransformedTouchEvent方法毙籽，注意第三個(gè)參數(shù)為null
//6.查看dispatchTransformedTouchEvent洞斯，發(fā)現(xiàn)它調(diào)用了super.dispatchTouchEvent，也就是View的dispatchTouchEvent
//7.View的dispatchTouchEvent下文還會(huì)仔細(xì)講解坑赡，它最終將事件交給了onTouch烙如，onTouchEvent么抗，onClick方法
//8.所以我們得出以下結(jié)論：如果ViewGroup的onInterceptTouchEvent，事件不會(huì)傳遞給子View厅翔，而是交給了自己的onTouch乖坠，onTouchEvent，onClick方法處理
//9.Down事件結(jié)束之后刀闷，MOve和Up到來時(shí),actionMasked == MotionEvent.ACTION_DOWN為false熊泵，mFirstTouchTarget != null也是false，事件不會(huì)再進(jìn)入onInterceptTouchEvent甸昏，而是直接交給當(dāng)前ViewGroup處理了
//-----------------------------------------------------------
//如果onInterceptTouchEvent返回false顽分，流程如下：
//1.Down事件到來，必定會(huì)進(jìn)入intercepted = onInterceptTouchEvent(ev);
//2.ViewGroup不消費(fèi)事件施蜜，intercepted被賦值為false卒蘸，必定會(huì)進(jìn)入###--->1出的if代碼塊
//3.運(yùn)行到###--->4處，會(huì)對(duì)遍歷子View翻默，如果找到了攔截該事件的對(duì)象缸沃，在###--->3處的addTouchTarget方法內(nèi)對(duì)mFirstTouchTarget進(jìn)行賦值，并指向了當(dāng)前ViewGroup的子元素修械。
//4.找到事件的攔截者并賦值給mFirstTouchTarget之后趾牧，繼續(xù)向下運(yùn)行到 ###--->5，此時(shí)mFirstTouchTarge肯污！=null翘单，執(zhí)行else分支，在###--->6 處將事件交給了當(dāng)前View的child來處理
//5.Down事件結(jié)束之后蹦渣，MOve和Up到來時(shí)哄芜，mFirstTouchTarget仍然持有Target，所以下面的if滿足mFirstTouchTarget != null柬唯，繼續(xù)詢問ViewGroup是否攔截事件
//6.MOve和Up的傳遞流程繼續(xù)重復(fù)了Down事件的流程
/******************************************************************************/
/*/ 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;
/*/ }
/******************************************************************************/
......
// 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;
###--->1 if (!canceled && !intercepted) {
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
......
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;
###--->4 for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
......
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();
###--->3 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();
}
......
}
}
//以下部分用于傳遞事件认臊，到這里時(shí)已經(jīng)找到了處理事件的對(duì)象，只是將事件交付給相應(yīng)的對(duì)象來處理
// Dispatch to touch targets.
###--->2 if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
###--->5 } 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;
###--->6 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;
}
通過對(duì)上邊代碼的分析锄奢，我們可以得到以下結(jié)論：
1.所有的ACTION_DOWN都會(huì)進(jìn)入onInterceptTouchEvent方法美尸，由ViewGroup判斷是否攔截，如果ViewGroup攔截了ACTION_DOWN斟薇，后續(xù)動(dòng)作(ACTION_MOVE,UP)都會(huì)交給ViewGroup處理师坎，不會(huì)再進(jìn)入onInterceptTouchEvent，這時(shí)候ViewGroup的onTouchEvent方法就會(huì)被調(diào)用堪滨，
2.如果ACTION_DOWN事件交給了ViewGroup的子View進(jìn)行處理胯陋，后續(xù)動(dòng)作(ACTION_MOVE,UP)仍然會(huì)進(jìn)入onInterceptTouchEvent，有可能會(huì)被ViewGroup攔截。子元素可以通過mParent.requestDisallowInterceptTouchEvent方法限制ViewGroup消耗事件（不進(jìn)入Intercept）遏乔，但是對(duì)ACTION_DOWN不起作用义矛。
3.ViewGroup攔截的事件會(huì)傳遞到View.dispatchTouchEvent，然后再由View傳遞給onTouch或onTouchEvent盟萨。ViewGroup并沒有覆寫onTouchEvent凉翻，onTouch等方法。
View#DispatchTouchEvent源碼分析
這里的View通常指單一View捻激，當(dāng)事件傳遞到這里的時(shí)候制轰，說明事件已經(jīng)通過ViewGroup找到了對(duì)應(yīng)的攔截方，View的DispatchTouchEvent只負(fù)責(zé)交付事件胞谭，所以代碼也相對(duì)簡(jiǎn)單：
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;
}
}
......
return result;
}
首先垃杖，會(huì)對(duì)onTouchListener進(jìn)行判斷，如果onTouchListener中的onTouch方法返回了true丈屹，onTouchEvent就不會(huì)再執(zhí)行了调俘。
再來看onTouchEvent方法：
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (event.getAction() == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
setPressed(false);
}
// A disabled view that is clickable still consumes the touch
// events, it just doesn't respond to them.
return (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE));
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
如果View是Disabled狀態(tài)，它仍然會(huì)消耗事件（CLICKABLE和LONG_CLICKABLE任一個(gè)為true）旺垒。
然后是代理的判斷彩库。繼續(xù)往下看源碼：
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
switch (event.getAction()) {
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 (!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();
}
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();
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;
從上邊的代碼可以發(fā)現(xiàn)，只要View的LONG_CLICKABLE或者CLICKABLE任一個(gè)為true（View的LONG_CLICKABLE默認(rèn)為false先蒋，CLICKABLE針對(duì)不同view默認(rèn)值不同）侧巨，view就會(huì)消耗事件。只有在ACTION_UP的時(shí)候鞭达，才會(huì)執(zhí)行onClick。
另外皇忿，setOnClickListener和setOnLongClickListener會(huì)自動(dòng)將View的CLICKABLE畴蹭，CLICKABLE設(shè)置為true。
