基礎(chǔ)知識(shí)
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事件分發(fā)的對(duì)象
事件分發(fā)的對(duì)象是 點(diǎn)擊事件（Touch事件）陶夜，當(dāng)用戶觸摸屏幕（View或者ViewGroup派生控件）時(shí)，將會(huì)產(chǎn)生點(diǎn)擊事件（Touch事件）
Touch事件的相關(guān)細(xì)節(jié)寇钉，如觸摸位置攘烛、時(shí)間等被封裝為MotionEvent對(duì)象
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事件類型
MotionEvent.ACTION_DOWN----按下View（所有事件的開(kāi)始）
MotionEvent.ACTION_MOVE----滑動(dòng)View
MotionEvent.ACTION_UP----抬起View
MotionEvent.ACTION_CANCEL----結(jié)束事件（所有事件的開(kāi)始）
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事件列
image.png
一般，事件列都是以DOWN事件開(kāi)始评抚，UP事件結(jié)束豹缀，中間無(wú)數(shù)個(gè)MOVE事件
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事件分發(fā)的本質(zhì)
將點(diǎn)擊事件MotionEvent傳遞到具體某個(gè)View以及處理該事件的整個(gè)過(guò)程
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事件分發(fā)在哪些對(duì)象間進(jìn)行傳遞
image.png
Activity----控制生命周期伯复，處理事件
View----所有UI組件的基類
ViewGroup----一組View的集合，本身也是View的子類
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事件分發(fā)的順序
Activity -> ViewGroup -> View
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事件分發(fā)由哪些主要方法協(xié)作完成
1邢笙、dispatchTouchEvent()
分發(fā)（傳遞）事件
當(dāng)點(diǎn)擊事件能夠傳遞到當(dāng)前View,該方法就會(huì)被調(diào)用
2啸如、onTouchEvent()
處理點(diǎn)擊事件
在dispatchTouchEvent方法內(nèi)部調(diào)用
3、onInterceptTouchEvent()
判斷是否攔截事件
該方法只存在于ViewGroup中氮惯，在ViewGroup的dispatchTouchEvent方法內(nèi)部調(diào)用叮雳。若是重新該方法為true，則表示父容器攔截了事件妇汗，子容器View將無(wú)法處理該事件
源碼流程分析
當(dāng)點(diǎn)擊事件發(fā)生后帘不，事件先傳到Activity、再傳到ViewGroup杨箭、最終傳到View
image.png
從上圖可知寞焙，要充分理解事件分發(fā)機(jī)制，本質(zhì)上是需要理解：
1互婿、Activity對(duì)點(diǎn)擊事件的分發(fā)機(jī)制
2捣郊、ViewGroup對(duì)點(diǎn)擊事件的分發(fā)機(jī)制
3、View對(duì)點(diǎn)擊事件的分發(fā)機(jī)制
下面我們將對(duì)這三個(gè)分發(fā)機(jī)制進(jìn)行逐一分析
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Activity對(duì)點(diǎn)擊事件的分發(fā)機(jī)制
當(dāng)點(diǎn)擊事件發(fā)生時(shí)慈参，最先響應(yīng)的是Activity的dispatchTouchEvent方法呛牲，那么為什么是它最先響應(yīng)呢？Activity之dispatchTouchEvent前傳
public boolean dispatchTouchEvent(MotionEvent ev) {
// 事件都是以按下事件（DOWN）為開(kāi)始驮配，所以此處為true
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction(); // 分析1
}
if (getWindow().superDispatchTouchEvent(ev)) { // 分析2
return true;
}
return onTouchEvent(ev); // 分析3
}
- 分析1(當(dāng)前在Activity類)
onUserInteraction();
// onUserInteraction方法是一個(gè)空方法娘扩，主要作用是實(shí)現(xiàn)屏保功能
// 當(dāng)此activity在棧頂時(shí)，觸屏點(diǎn)擊按home壮锻，back畜侦，recent鍵等都會(huì)觸發(fā)此方法
public void onUserInteraction() {}
- 分析2(當(dāng)前在Activity類)
getWindow().superDispatchTouchEvent(ev)
// getWindow方法返回 mWindow，它是一個(gè)PhoneWindow對(duì)象
public Window getWindow() {
return mWindow;
}
private Window mWindow;
// PhoneWindow為Window抽象類的子類
mWindow = new PhoneWindow(this, window, activityConfigCallback);
- 分析2(當(dāng)前在Window類)
// 抽象方法躯保，由PhoneWindow類實(shí)現(xiàn)
public abstract boolean superDispatchTouchEvent(MotionEvent event);
- 分析2(當(dāng)前在PhoneWindow類)
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
// 調(diào)用DecorView類中的superDispatchTouchEvent方法
return mDecor.superDispatchTouchEvent(event);
}
private DecorView mDecor;
- 分析2(當(dāng)前在DecorView類)
// 調(diào)用父類的dispatchTouchEvent方法
// DecorView是所有UI界面的父類
// DecorView的父類是FrameLayout睬关，但FrameLayout并沒(méi)有實(shí)現(xiàn)dispatchTouchEvent方法
// 所以繼續(xù)向上尋找到FrameLayout的父類专执，即調(diào)用ViewGroup類的dispatchTouchEvent方法
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
此時(shí)，事件被分發(fā)到了ViewGroup
- 分析3(當(dāng)前在Activity類)
return onTouchEvent(ev);
// 當(dāng)點(diǎn)擊事件未被任何一個(gè)View接收并處理就會(huì)執(zhí)行onTouchEvent方法
// 場(chǎng)景如：發(fā)生在Window邊界外的觸摸事件
public boolean onTouchEvent(MotionEvent event) {
// 點(diǎn)擊事件發(fā)生在Windows邊界外吭服，返回true
if (mWindow.shouldCloseOnTouch(this, event)) {
finish();
return true;
}
return false;
}
- 分析3(當(dāng)前在Window類)
public boolean shouldCloseOnTouch(Context context, MotionEvent event) {
// 主要是對(duì)于處理邊界外點(diǎn)擊事件的判斷：是否是DOWN事件擅羞，event的坐標(biāo)是否在邊界內(nèi)等
final boolean isOutside =
event.getAction() == MotionEvent.ACTION_DOWN && isOutOfBounds(context, event)
|| event.getAction() == MotionEvent.ACTION_OUTSIDE;
if (mCloseOnTouchOutside && peekDecorView() != null && isOutside) {
// 說(shuō)明事件在邊界外尸变，即 消費(fèi)事件
return true;
}
// 未消費(fèi)（默認(rèn)）
return false;
}
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Activity對(duì)點(diǎn)擊事件的分發(fā)機(jī)制總結(jié)
image.png
至此，流程已經(jīng)走到了ViewGroup類中的dispatchTouchEvent方法减俏，繼續(xù)分析~
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ViewGroup對(duì)點(diǎn)擊事件的分發(fā)機(jī)制
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
// 這是一個(gè)驗(yàn)證事件完整性的一個(gè)類,一會(huì)會(huì)看到在本方法結(jié)束的地方也有這個(gè)類出現(xiàn)
// 防止event事件在分發(fā)過(guò)程中不一致,這個(gè)類還有記錄的功能
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.
// 檢測(cè)無(wú)障礙焦點(diǎn)
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {// 分析1
// 獲取Touch Action
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) { // 分析2
// 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.
// 判斷事件是否需要攔截
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
// 判斷是否運(yùn)行不允許攔截
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
// 如果允許攔截
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev); // 分析3
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) {// 分析4
// If the event is targeting accessibility 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;
for (int i = childrenCount - 1; i >= 0; i--) { // 分析8
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;
}
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) {// 分析5
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {// 分析6
// 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;
}
- 分析1(當(dāng)前在View類)
// 檢測(cè)是否分發(fā)Touch事件（判斷窗口是否被遮擋渍倮谩）
// 如果該 Touch 事件沒(méi)有被窗口遮擋，則繼續(xù)后續(xù)邏輯
// 一般情況下都會(huì)返回true
public boolean onFilterTouchEventForSecurity(MotionEvent event) {
if ((mViewFlags & FILTER_TOUCHES_WHEN_OBSCURED) != 0
&& (event.getFlags() & MotionEvent.FLAG_WINDOW_IS_OBSCURED) != 0) {
// Window is obscured, drop this touch.
return false;
}
return true;
}
- 分析2(當(dāng)前在ViewGroup類）
// 判斷當(dāng)前是否是ACTION_DOWN娃承，剛進(jìn)來(lái)的時(shí)候肯定是ACTION_DOWN
if (actionMasked == MotionEvent.ACTION_DOWN) {
cancelAndClearTouchTargets(ev);
resetTouchState();
}
private void cancelAndClearTouchTargets(MotionEvent event) {
....
clearTouchTargets();
....
}
// 將mFirstTouchTarget置為null
// 回收TouchTarget對(duì)象
// 清空所有接收觸摸事件View的引用
private void clearTouchTargets() {
// TouchTarget和Handler中的Message一樣奏夫，都是一個(gè)單向鏈表怕篷，鏈?zhǔn)浇Y(jié)構(gòu)，通過(guò)next來(lái)訪問(wèn)下一個(gè)元素
TouchTarget target = mFirstTouchTarget;
if (target != null) {
do {
TouchTarget next = target.next;
target.recycle();
target = next;
} while (target != null);
mFirstTouchTarget = null;
}
}
private void resetTouchState() {
clearTouchTargets();
resetCancelNextUpFlag(this);
// 默認(rèn)允許攔截事件
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
// 默認(rèn)視圖不滾動(dòng)
mNestedScrollAxes = SCROLL_AXIS_NONE;
}
- 分析3(當(dāng)前在ViewGroup類中)
public boolean onInterceptTouchEvent(MotionEvent ev) {
// 通常不會(huì)執(zhí)行下面的語(yǔ)句
if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
&& ev.getAction() == MotionEvent.ACTION_DOWN
&& ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
&& isOnScrollbarThumb(ev.getX(), ev.getY())) {
return true;
}
// 默認(rèn)返回false
return false;
}
通常酗昼，如果ViewGroup或其派生類重寫(xiě)了onInterceptTouchEvent并返回為true廊谓，這說(shuō)明父容器需要攔截當(dāng)前點(diǎn)擊事件，即onInterceptTouchEvent為true麻削。
代碼到了這里蒸痹，出現(xiàn)了一個(gè)分支：
即，如果onInterceptTouchEvent為true呛哟，則執(zhí)行 [分析4]叠荠，否則不執(zhí)行。
接下來(lái)我們先分析父容器攔截事件的情況扫责。
- 分析5(當(dāng)前在ViewGroup類)
// 此時(shí) mFirstTouchTarget必定為null榛鼎，因?yàn)橹罢{(diào)用cancelAndClearTouchTargets方法時(shí)做了清空處理
// mFirstTouchTarget必定為null，意味著 沒(méi)有任何 view 消費(fèi)該 Touch 事件
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
// ev: event事件類型
// canceled：是否是cancel公给，因?yàn)闆](méi)有取消借帘，所以當(dāng)前是false
// null：View child字段傳了null
// TouchTarget.ALL_POINTER_IDS：位置
// viewGroup 會(huì)調(diào)用dispatchTransformedTouchEvent處理，但是child==null淌铐，會(huì)調(diào)用View#dispatchTouchEvent處理
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS); // 分析5-1
}
- 分析5-1(當(dāng)前在ViewGroup類)
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();
// cancel為false肺然，下方if語(yǔ)句塊不會(huì)執(zhí)行
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
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;
// 下面if語(yǔ)句塊是一個(gè)新老事件的處理，也不會(huì)進(jìn)入
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
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) {
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;
}
由于child傳進(jìn)來(lái)為null腿准，所以調(diào)用了super.dispatchTouchEvent方法际起，而ViewGroup類的父類是View，所以這里進(jìn)入并執(zhí)行了View類中的dispatchTouchEvent方法吐葱。
當(dāng)前 handler返回為true(邏輯見(jiàn)View的事件分發(fā)機(jī)制流程分析)街望，則回到 [分析5]處， [分析5]的代碼也會(huì)返回true弟跑，則會(huì)回到Activity的dispatchEvent方法中灾前。
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
getWindow().superDispatchTouchEvent(ev)返回為true，至此孟辑，在“父容器攔截事件”的情況下的流程已經(jīng)走完哎甲。
下面分析父容器不攔截子View事件的情況
再次展示VIewGroup的dispatchTouchEvent方法的代碼
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
// 這是一個(gè)驗(yàn)證事件完整性的一個(gè)類,一會(huì)會(huì)看到在本方法結(jié)束的地方也有這個(gè)類出現(xiàn)
// 防止event事件在分發(fā)過(guò)程中不一致,這個(gè)類還有記錄的功能
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.
// 檢測(cè)無(wú)障礙焦點(diǎn)
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {// 分析1
// 獲取Touch Action
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) { // 分析2
// 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.
// 判斷事件是否需要攔截
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
// 判斷是否運(yùn)行不允許攔截
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
// 如果允許攔截
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev); // 分析3
ev.setAction(action); // restore action in case it was changed
} else {
// 不攔截狀態(tài)下，intercepted = false
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) {// 分析4
// If the event is targeting accessibility 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;
// 因?yàn)檫€是處于按下?tīng)顟B(tài)饲嗽，所以當(dāng)前為ACTION_DOWN
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);
// 對(duì)于當(dāng)前事件炭玫，有處理權(quán)限的View的個(gè)數(shù)（肯定不為0）
final int childrenCount = mChildrenCount;
// 因?yàn)閚ewTouchTarget還未賦值，所以為null
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();// 分析7
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
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;
}
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) {// 分析5
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {// 分析6
// 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;
}
父容器不攔截子View事件貌虾，intercepted 為 false吞加，canceled也為false，在[分析4]處的代碼塊會(huì)被執(zhí)行
- 分析7(當(dāng)前在ViewGroup類)
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
public ArrayList<View> buildTouchDispatchChildList() {
return buildOrderedChildList();
}
ArrayList<View> buildOrderedChildList() {
final int childrenCount = mChildrenCount;
if (childrenCount <= 1 || !hasChildWithZ()) return null;
if (mPreSortedChildren == null) {
mPreSortedChildren = new ArrayList<>(childrenCount);
} else {
// callers should clear, so clear shouldn't be necessary, but for safety...
mPreSortedChildren.clear();
mPreSortedChildren.ensureCapacity(childrenCount);
}
final boolean customOrder = isChildrenDrawingOrderEnabled();
for (int i = 0; i < childrenCount; i++) {
// add next child (in child order) to end of list
final int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);
final View nextChild = mChildren[childIndex];
final float currentZ = nextChild.getZ();
// insert ahead of any Views with greater Z
int insertIndex = i;
while (insertIndex > 0 && mPreSortedChildren.get(insertIndex - 1).getZ() > currentZ) {
insertIndex--;
}
mPreSortedChildren.add(insertIndex, nextChild);
}
return mPreSortedChildren;
}
對(duì)當(dāng)前有處理事件權(quán)限的View做一個(gè)排序，將View按照getZ()方法為排序依據(jù)一個(gè)個(gè)的放入ArrayList數(shù)組中
getZ方法拿到的是View的Z坐標(biāo)衔憨，getZ越大叶圃，在數(shù)組中的位置越靠后。
image.png
如果一個(gè)Activity中包含一個(gè)LinearLayout巫财，LinearLayout中有子View為Button盗似，那么數(shù)組的排序?yàn)锳ctivity、LinearLayout平项、Button赫舒。
在[分析7]處，依據(jù)拿到了排過(guò)序的ArrayList闽瓢，進(jìn)入[分析8]
- 分析8(當(dāng)前在ViewGroup類)
// 這里做了倒序處理(如上圖接癌，就是先把Button取出來(lái)了)
for (int i = childrenCount - 1; i >= 0; i--) {
// 獲取child對(duì)應(yīng)的index
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
// 從數(shù)組中獲取View
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
...
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) { // 分析8-1
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child); // 分析8-2
...
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {// 分析8-3
// 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;
}
}
- 分析8-1(當(dāng)前在ViewGroup類)
// 如果是View不可見(jiàn)或者正在執(zhí)行動(dòng)畫(huà)，則返回false扣讼；否則返回true
private static boolean canViewReceivePointerEvents(@NonNull View child) {
return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null;
}
// 判斷當(dāng)前位置
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;
}
[分析8-1]處的代碼缺猛，主要是分析當(dāng)前View是否符合處理事件的條件，如果不符合椭符，continue荔燎。
- 分析8-2(當(dāng)前在ViewGroup類)
newTouchTarget = getTouchTarget(child);
private TouchTarget getTouchTarget(@NonNull View child) {
for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
if (target.child == child) {
return target;
}
}
return null;
}
由于mFirstTouchTarget目前暫未賦值，還是為null销钝，所以方法體返回null有咨，即newTouchTarget為null
- 分析8-3(當(dāng)前在ViewGroup類)
這次流程進(jìn)入了dispatchTransformedTouchEvent方法中，和之前遇到的[分析5-1]代碼流程不同蒸健，這時(shí)的第三個(gè)入?yún)iew child是有值的座享，按照之前分析的流程來(lái)看，這里傳入的應(yīng)該是button似忧。
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);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
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()) {
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.
// 此時(shí)child不為null
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
// 偏移處理
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
transformedEvent.offsetLocation(offsetX, offsetY);
if (! child.hasIdentityMatrix()) {
transformedEvent.transform(child.getInverseMatrix());
}
// 重點(diǎn)代碼渣叛，調(diào)用了child(也就是View)的dispatchTouchEvent方法。
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
調(diào)用 child.dispatchTouchEvent方法盯捌，流程就進(jìn)入到了View類中的 dispatchTouchEvent方法里了
dispatchTransformedTouchEvent方法會(huì)返回true,也就是[分析8-3]處的代碼返回為true淳衙，進(jìn)入if語(yǔ)句塊。
再次放出[分析8-3]處if語(yǔ)句塊中代碼
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); // 分析9
alreadyDispatchedToNewTouchTarget = true;
// 跳出for循環(huán)
break;
}
我們知道饺著，如果是子View處理了事件滤祖，那么其父容器是無(wú)法處理該事件的，為什么呢瓶籽？我們繼續(xù)分析addTouchTarget方法
- 分析9(當(dāng)前在ViewGroup類)
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
// 根據(jù)child獲取到TouchTarget
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
// 此時(shí) mFirstTouchTarget依然為null，所以target.next為null
target.next = mFirstTouchTarget;
// target賦值給mFirstTouchTarget埂材，此時(shí)mFirstTouchTarget不為null
mFirstTouchTarget = target;
return target;
}
public static TouchTarget obtain(@NonNull View child, int pointerIdBits) {
...
final TouchTarget target;
// 同步方法
synchronized (sRecycleLock) {
if (sRecycleBin == null) {
// 首次進(jìn)來(lái) new 一個(gè)TouchTarget
target = new TouchTarget();
} else {
target = sRecycleBin;
sRecycleBin = target.next;
sRecycledCount--;
target.next = null;
}
}
// 傳進(jìn)來(lái)的View賦值給target.child塑顺，并將target返回出去
target.child = child;
target.pointerIdBits = pointerIdBits;
return target;
}
此時(shí)再看[分析8-3]處的代碼:
newTouchTarget不為null，
newTouchTarget.next為null，
mFirstTouchTarget不為null,
mFirstTouchTarget.next為null严拒，
且newTouchTarget = mFirstTouchTarget扬绪，
alreadyDispatchedToNewTouchTarget為true
根據(jù)剛才我們得到的結(jié)果，可以看到流程已經(jīng)開(kāi)始執(zhí)行下面代碼
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
// 首次target不為null
while (target != null) {
// 由于 target.next為null裤唠，此時(shí)next為null
final TouchTarget next = target.next;
// alreadyDispatchedToNewTouchTarget為true
// target == newTouchTarget根據(jù)之前分析的為true
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
// handled為true
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;
// 將next賦值給target挤牛，而此時(shí)的next為null，所以target為null种蘸，跳出while循環(huán)
target = next;
}}
流程到此墓赴，ViewGroup的dispatchTouchEvent方法返回為true, 則回到 [分析5]處， [分析5]的代碼也會(huì)返回true航瞭，則會(huì)回到Activity的dispatchEvent方法中诫硕。
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
getWindow().superDispatchTouchEvent(ev)返回為true，至此刊侯，在“父容器不攔截事件”的情況下的流程已經(jīng)走完章办。
-
ViewGroup對(duì)點(diǎn)擊事件的分發(fā)機(jī)制總結(jié)
image.png
-
View對(duì)點(diǎn)擊事件的分發(fā)機(jī)制
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();
}
// 檢測(cè)是否分發(fā)Touch事件（判斷窗口是否被遮擋住）
// 如果該 Touch 事件沒(méi)有被窗口遮擋滨彻，則繼續(xù)后續(xù)邏輯
// 一般情況下都會(huì)返回true
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo; // 分析10
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {// 分析11
result = true;
}
if (!result && onTouchEvent(event)) {// 分析12
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;
}
- 分析10(當(dāng)前在View類)
ListenerInfo li = mListenerInfo;
那么mListenerInfo是在哪里賦值的呢藕届？
- 分析10(當(dāng)前在View類)
ListenerInfo getListenerInfo() {
if (mListenerInfo != null) {
return mListenerInfo;
}
mListenerInfo = new ListenerInfo();
return mListenerInfo;
}
繼續(xù)尋找getListenerInfo方法調(diào)用的地方
- 分析10(當(dāng)前在View類)
public void setOnClickListener(@Nullable OnClickListener l) {
if (!isClickable()) {
setClickable(true);
}
getListenerInfo().mOnClickListener = l;
}
setOnClickListener方法是Android開(kāi)發(fā)者最最常用的一個(gè)方法了，執(zhí)行此方法亭饵，傳遞一個(gè)OnClickListener進(jìn)來(lái)休偶。
- 分析11(當(dāng)前在View類)
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
- 分析12(當(dāng)前在View類)
if (!result && onTouchEvent(event)) {
result = true;
}
[分析11]和[分析12]可以結(jié)合起來(lái)看，如果某個(gè)View重寫(xiě)了onTouch方法并返回為true冬骚，就不能執(zhí)行onTouchEvent方法椅贱。也就是說(shuō)執(zhí)行了[分析11]處的代碼，[分析12]就不會(huì)執(zhí)行了只冻。
當(dāng)然庇麦，如果不重寫(xiě)onTouch，或者onTouch方法返回false喜德，就會(huì)執(zhí)行[分析12]處的onTouchEvent山橄。我們經(jīng)常使用的onClick方法就是在此。
public boolean onTouchEvent(MotionEvent event) {
...
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
switch (action) {
// 如果是點(diǎn)擊事件舍悯，就得滿足先DOWN后UP
// 那么就可以直接在ACTION_UP中查看方法
case MotionEvent.ACTION_UP:
...
performClickInternal();
...
case MotionEvent.ACTION_DOWN:
...
}
return true;
}
return false;
}
查看performClickInternal方法源碼
private boolean performClickInternal() {
notifyAutofillManagerOnClick();
return performClick();
}
繼續(xù)查看performClick方法源碼
public boolean performClick() {
notifyAutofillManagerOnClick();
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;
}
可以看到航棱，這里執(zhí)行了OnClickListener接口的onClick回調(diào)，也就是我們經(jīng)常使用的onClick方法了萌衬。
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View對(duì)點(diǎn)擊事件的分發(fā)機(jī)制總結(jié)
image.png
