Android進階知識：事件分發與滑動衝突（二）

接著看代碼塊3，在這段很長的代碼里，首先一個if中判斷了該事件是否滿足沒有被攔截和被取消，之後第二個if判斷了事件類型是否為DOWN，滿足了沒有被攔截和取消的DOWN事件，接下來ViewGroup才會循環其子View找到點擊事件在其內部並且能夠接受該事件的子View，再通過調用dispatchTransformedTouchEvent方法將事件分發給該子View處理，返回true說明子View成功消費事件，於是調用addTouchTarget方法，方法中通過TouchTarget.obtain方法獲得一個包含這View的TouchTarget節點並將其添加到鏈表頭，並將已經分發的標記設置為true。

接下來看代碼塊4：

// Dispatch to touch targets. //走到這裡說明在循環遍歷所有子View後沒有找到接受該事件或者事件不是DOWN事件或者該事件已被攔截或取消 if (mFirstTouchTarget == null) { //mFirstTouchTarget為空說明沒有子View響應消費該事件 //所有調用dispatchTransformedTouchEvent方法分發事件 //注意這裡第三個參數傳的是null，方法里會調用super.dispatchTouchEvent(event)即View.dispatchTouchEvent(event)方法 // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); } else { // mFirstTouchTarget不為空說明有子View能響應消費該事件，消費過之前的DOWN事件，就將這個事件還分發給這個View // 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; //這裡傳入的是target.child就是之前響應消費的View，把該事件還交給它處理 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; } }

之前在代碼塊3中處理分發了沒被攔截和取消的DOWN事件，那麼其他MOVE、UP等類型事件怎麼處理呢？還有如果遍歷完子View卻沒有能接受這個事件的View又怎麼處理呢？代碼塊4中就處理分發了這些事件。首先判斷mFirstTouchTarget是否為空，為空說明沒有子View消費該事件，於是就調用dispatchTransformedTouchEvent方法分發事件，這裡注意dispatchTransformedTouchEvent方法第三個參數View傳的null，方法里會對於這種沒有子View能處理消費事件的情況，就調用該ViewGroup的super.dispatchTouchEvent方法，即View的dispatchTouchEvent，把ViewGroup當成View來處理，把事件交給ViewGroup處理。具體看dispatchTransformedTouchEvent方法中的這段代碼：

if (child == null) { handled = super.dispatchTouchEvent(event); } else { handled = child.dispatchTouchEvent(event); }

dispatchTransformedTouchEvent方法中child即傳入的View為空則調用super.dispatchTouchEvent方法分發事件，就是View類的分發方法，不為空則調用子View方法，即child.dispatchTouchEvent分發事件，所以歸根結底都是調用了View類的dispatchTouchEvent方法處理。

至此，ViewGroup中的分發過流程結束，再來總結一下這個過程：首先過濾掉不安全的事件，接著如果事件類型是DOWN事件認為是一個新的事件序列開始，就清空TouchTarget鏈表重置相關標誌位（代碼塊一），然後判斷是否攔截該事件，這裡有兩步判斷：一是如果是DOWN事件或者不是DOWN事件但是mFirstTouchTarget不等於null（這裡mFirstTouchTarget如果等於null說明之前沒有View消費DOWN事件，在代碼塊三末尾，可以看到如果有子View消費了DOWN事件，會調用addTouchTarget方法，獲得一個保存了該子View的TouchTarget，並將其添加到mFirstTouchTarget鏈表頭），則進入第二步禁止攔截標記的判斷，否則直接設置為需要攔截，進入第二步判斷設置過禁止攔截標記為true的就不攔截，否則調用ViewGroup的onInterceptTouchEvent方法根據返回接過來決定是否攔截（代碼塊二）。接下來如果事件沒被攔截也沒被取消而且還是DOWN事件，就循環遍歷ViewGroup中的子View找到事件在其範圍內並且能接受事件的子View，通過dispatchTransformedTouchEvent方法將事件分發給該子View，然後通過addTouchTarget方法將包含該子View的TouchTarget插到鏈表頭（代碼塊三）。最後如果沒有找到能夠接受該事件的子View又或者是MOVE、UP類型事件等再判斷mFirstTouchTarget是否為空，為空說明之前沒有View能接受消費該事件，則調用dispatchTransformedTouchEvent方法將事件交給自身處理，不為空則同樣調用dispatchTransformedTouchEvent方法，但是是將事件分發給該子View處理。

ViewGroup的onInterceptTouchEvent方法：

public boolean onInterceptTouchEvent(MotionEvent ev) { if (ev.isFromSource(InputDevice.SOURCE_MOUSE) && ev.getAction() == MotionEvent.ACTION_DOWN && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY) && isOnScrollbarThumb(ev.getX(), ev.getY())) { return true; } return false; }

在ViewGroup的dispatchTouchEvent中沒設置過禁止攔截的事件默認都會通過onInterceptTouchEvent方法來決定是否攔截，onInterceptTouchEvent方法里可以看到默認是返回false，只有在事件源類型是滑鼠並且是DOWN事件是滑鼠點擊按鈕和是滾動條的手勢時才返回true。所以默認一般ViewGroup的onInterceptTouchEvent方法返回都為false，也就是說默認不攔截事件。

ViewGroup的onTouchEvent方法：

ViewGroup中沒有覆蓋onTouchEvent方法，所以調用ViewGroup的onTouchEvent方法實際上調用的還是它的父類View的onTouchEvent方法。

View的dispatchTouchEvent方法：

在ViewGroup中將事件無論是分發給子View的時候還是自己處理的，最終都會執行默認的View類的dispatchTouchEvent方法：

public boolean dispatchTouchEvent(MotionEvent event) { ...... boolean result = false; ...... if (onFilterTouchEventForSecurity(event)) {

......

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;
}

這裡同樣省略一些代碼只看關鍵的，首先同樣和ViewGroup一樣，做了事件安全性的過濾，接著先判斷了mOnTouchListener是否為空，不為空並且該View是ENABLED可用的，就會調用mOnTouchListener的onTouch方法，如果onTouch方法返回true說明事件已經被消費了，就將result標記修改為true，這樣他就不會走接下來的if了。如果沒有設置mOnTouchListener或者onTouch方法返回false，則會繼續調用onTouchEvent方法。這裡可以發現mOnTouchListener的onTouch方法的優先順序是在onTouchEvent之前的，如果在代碼中設置了mOnTouchListener監聽，並且onTouch返回true，則這個事件就被在onTouch里消費了，不會在調用onTouchEvent方法。

//這個mOnTouchListener就是經常在代碼里設置的View.OnTouchListener mMyView.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { //這裡返回true事件就消費了，不會再調用onTouchEvent方法 return true; } });

View的onTouchEvent方法：

public boolean onTouchEvent(MotionEvent event) { /---------------代碼塊-1------------------------------------------------------------------- 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;

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 doesnt respond to them.
return clickable;
}
/---------------代碼塊-1------完-------------------------------------------------------------
/---------------代碼塊-2-------------------------------------------------------------------
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
/---------------代碼塊-2------完-------------------------------------------------------------
/---------------代碼塊-3-------------------------------------------------------------------
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 dont 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)) {
//調用了OnClickListener
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 were 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;
}

return true;
}
/---------------代碼塊-3------完-------------------------------------------------------------
return false;
}

onTouchEvent方法里的代碼也不少，不過大部分都是響應事件的一些邏輯，與事件分發流程關係不大。還是分成三塊，先看第一個代碼塊：

final float x = event.getX(); final float y = event.getY(); final int viewFlags = mViewFlags; final int action = event.getAction(); //這裡CLICKABLE、CONTEXT_CLICKABLE和CONTEXT_CLICKABLE有一個滿足，clickable就為true final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE; //這裡先判斷當前View是否可用，如果是不可用進入if代碼塊 if ((viewFlags & ENABLED_MASK) == DISABLED) { //如果是UP事件並且View處於PRESSED狀態，則調用setPressed設置為false 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 doesnt respond to them. //這裡如果View是不可用狀態，就直接返回clickable狀態，不做任何處理 return clickable; }

代碼塊1中首先獲得View是否可點擊clickable，然後判斷View如果是不可用狀態就直接返回clickable，但是沒做任何響應。View默認的clickable為false，Enabled為ture，不同的View的clickable默認值也不同，Button默認clickable為true，TextView默認為false。

if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } }

代碼塊2中會對一個mTouchDelegate觸摸代理進行判斷，不為空會調用代理的onTouchEvent響應事件並且返回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 dont have it already and we should in // touch mode. boolean focusTaken = false; if (isFocusable() && isFocusableInTouchMode() && !isFocused()) { focusTaken = requestFocus(); }

if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();

if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}

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 were inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();

case MotionEvent.ACTION_MOVE:
if (clickable) {
drawableHotspotChanged(x, y);
}

return true;
}

代碼塊3中首先判斷了 clickable || (viewFlags & TOOLTIP) == TOOLTIP 滿足了這個條件就返回true消費事件。接下來的switch中主要對事件四種狀態分別做了處理。這裡稍微看下在UP事件中會調用一個performClick方法，方法中調用了OnClickListener的onClick方法。

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); notifyEnterOrExitForAutoFillIfNeeded(true); return result; }