Android中的事件分發機制基本認識
一、基礎認識
Android 中事件的傳遞流程:
Activity--------> Window(PhoneWindow)------>DecroView------->ViewGroup----->View;
二、Activity中事件分發
螢幕發生觸控事Android系統層接受到事件,然後反饋給此時棧頂的App的Acivity,並回調Activity中的dispatchTouchEvent(MotionEvent ev)函式,然後才是事件分發與消費;在Activity中事件分發程式碼十分簡單,原始碼入手:
Activity中dispatchTouchEvent(MotionEvent ev)原始碼:
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
根據原始碼先向Windows傳遞事件,如果Window的superDispatchTouchEvent(MotionEvent ev)如果返回true[消費事件],則函式立即返回,否則繼續呼叫Activity的onTouchEvent(MotionEvent ev)處理;
public boolean onTouchEvent(MotionEvent event) {
if (mWindow.shouldCloseOnTouch(this, event)) {
finish();
return true;
}
return false;
}
- 在Activity中可以直接是重新onTouchEvent函式實現攔截事件,需要注意的是根據dispatchTouchEvent中原始碼可知,如果需要在保證在Activiy的其他元件中不能攔截事件,否則Activity中dispatchTouchEvent函式就無效了。
三、 Window、DecorView中事件分發
PhonWindow中superDispatchTouchEvent(MotionEvent ev)原始碼;
根據Activity中的 dispatchTouchEvent(MotionEvent ev) 原始碼可知繼續向Window傳遞事件的,在Android中Window是一個抽象類並且只有PhoneWindow一個子類,所以直接看PhonWindow中的superDispatchTouchEvent(MotionEvent ev);
public boolean superDispatchTouchEvent(MotionEvent event) {
return this.mDecor.superDispatchTouchEvent(event);
}
顯然在PhoneWindow中是直接傳遞給DecorView中superDispatchTouchEvent(MotionEvent event)進行了進一步的分發的;繼續跟蹤DecorView中的原始碼:
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
四、 ViewGroup中事件分發
在原始碼分析之前寫理一下流程,然後在根據原始碼分段解析:
ViewGroup中事件分發函式dispatchTouchEvent(MotionEvent ev)的流程虛擬碼:
public boolean dispatchTouchEvent(MotionEvent ev) {
/* 事件連續性、頁面焦距的 安全性 check 過濾無效事件、清楚無效資料恢復狀態*/
.......
/*是否攔截、取消的判斷*/
if (actionMasked != 0 && this.mFirstTouchTarget == null) {
intercepted = true;
} else {
canceled = (this.mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!canceled)
intercepted = this.onInterceptTouchEvent(ev);//攔截呼叫onInterceptTouchEvent函式
}
/*如果當前事件沒有被攔擷取消,則繼續向下分發*/
if (!canceled && !intercepted) {
/*準備所以是childView,並且過濾出具體需要分發的childView,*/
.......
//向下分發的目標ChildView
ArrayList<View> preorderedList = this.buildTouchDispatchChildList();
.......
/*進行向childView分發事件*/
for(int i = childrenCount - 1; i >= 0; --i) {
/*對childView進行check是否可以接受事件、分發事件之前reset狀態,防止出現事件混亂【down、move、cancel……先後順序混亂】*/
.......
/*進行向下childView分發 ,dispatchTransformedTouchEvent具體分發函式*/
if (this.dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
/*記錄消費事件的目標ChildVewi的時間和在List<ChildVewi>位置*/
.......
/*記錄消費事件View的物件和指標*/
newTouchTarget = this.addTouchTarget(child, idBitsToAssign);
break;
}
/*如果在childView的List中沒有目標View【在觸控點選的位置沒字View控制元件,只有Layout】*/
if (this.mFirstTouchTarget == null) {
/* 呼叫ViewGroup的super.dispatchTouchEvent(event),就是呼叫ViewGroup的父類View的dispatchTouchEvent函式,
在View的dispatchTouchEvent然後回撥onTouchEvent(event) */
handled = this.dispatchTransformedTouchEvent(ev, canceled, (View)null, -1);
} else {
/*變數、物件的回收處理*/
.......
}
}}
return handled;
}
在上面的虛擬碼中已經把ViewGroup中的事件分發流程基本搞清楚,主要分為:
1.判斷是否攔截;
2.向ChildView分發事件;
ViewGroup中dispatchTouchEvent完整原始碼:
public boolean dispatchTouchEvent(MotionEvent ev) {
//驗證事件是否連續
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
//這個變數用於記錄事件是否被處理完
boolean handled = false;
//過濾掉一些不合法的事件:當前的View的視窗被遮擋了。
if (onFilterTouchEventForSecurity(ev)) {
//如果事件發生的View在的視窗,沒有被遮擋
final int action = ev.getAction();
//重置前面為0 ,只留下後八位,用於判斷相等時候,可以提高效能。
final int actionMasked = action & MotionEvent.ACTION_MASK;
//判斷是不是Down事件,如果是的話,就要做初始化操作
if (actionMasked == MotionEvent.ACTION_DOWN) {
//如果是down事件,就要清空掉之前的狀態,比如,重置手勢判斷什麼的。
//比如,之前正在判斷是不是一個單點的滑動,但是第二個down來了,就表示,不可能是單點的滑動,要重新開始判斷觸控的手勢
//清空掉mFirstTouchTarget
// 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();
}
//檢查是否攔截事件
final boolean intercepted;
//如果當前是Down事件,或者已經有處理Touch事件的目標了
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//判斷允不允許這個View攔截
//使用與運算作為判斷,可以讓我們在flag中,儲存好幾個標誌
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
//如果說允許攔截事件
if (!disallowIntercept) {
//確定是不是攔截了
intercepted = onInterceptTouchEvent(ev);
//重新恢復Action,以免action在上面的步驟被人為地改變了
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.
//如果說,事件已經初始化過了,並且沒有子View被分配處理,那麼就說明,這個ViewGroup已經攔截了這個事件
intercepted = true;
}
// Check for cancelation.
//如果viewFlag被設定了PFLAG_CANCEL_NEXT_UP_EVENT ,那麼就表示,下一步應該是Cancel事件
//或者如果當前的Action為取消,那麼當前事件應該就是取消了。
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
//如果需要(不是取消,也沒有被攔截)的話,那麼在觸控down事件的時候更新觸控目標列表
//split代表,當前的ViewGroup是不是支援分割MotionEvent到不同的View當中
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
//新的觸控物件,
TouchTarget newTouchTarget = null;
//是否把事件分配給了新的觸控
boolean alreadyDispatchedToNewTouchTarget = false;
//事件不是取消事件,也沒有攔截那麼就要判斷
if (!canceled && !intercepted) {
//如果是個全新的Down事件
//或者是有新的觸控點
//或者是游標來回移動事件(不太明白什麼時候發生)
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
//這個事件的索引,也就是第幾個事件,如果是down事件就是0
final int actionIndex = ev.getActionIndex(); // always 0 for down
//獲取分配的ID的bit數量
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.
//清理之前觸控這個指標標識,以防他們的目標變得不同步。
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
//如果新的觸控物件為null(這個不是鐵定的嗎)並且當前ViewGroup有子元素
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.
//下面所做的工作,就是找到可以接收這個事件的子元素
final View[] children = mChildren;
//是否使用自定義的順序來新增控制元件
final boolean customOrder = isChildrenDrawingOrderEnabled();
for (int i = childrenCount - 1; i >= 0; i--) {
//如果是用了自定義的順序來新增控制元件,那麼繪製的View的順序和mChildren的順序是不一樣的
//所以要根據getChildDrawingOrder取出真正的繪製的View
//自定義的繪製,可能第一個會畫到第三個,和第四個,第二個畫到第一個,這樣裡面的內容和Children是不一樣的
final int childIndex = customOrder ?
getChildDrawingOrder(childrenCount, i) : i;
final View child = children[childIndex];
//如果child不可以接收這個觸控的事件,或者觸控事件發生的位置不在這個View的範圍內
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
continue;
}
//獲取新的觸控物件,如果當前的子View在之前的觸控目標的列表當中就返回touchTarget
//子View不在之前的觸控目標列表那麼就返回null
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.
//如果新的觸控目標物件不為空,那麼就把這個觸控的ID賦予它,這樣子,
//這個觸控的目標物件的id就含有了好幾個pointer的ID了
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
//如果子View不在之前的觸控目標列表中,先重置childView的標誌,去除掉CACEL的標誌
resetCancelNextUpFlag(child);
//呼叫子View的dispatchTouchEvent,並且把pointer的id 賦予進去
//如果說,子View接收並且處理了這個事件,那麼就更新上一次觸控事件的資訊,
//並且為建立一個新的觸控目標物件,並且繫結這個子View和Pointer的ID
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
mLastTouchDownIndex = childIndex;
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}
}
//如果newTouchTarget為null,就代表,這個事件沒有找到子View去處理它,
//那麼,如果之前已經有了觸控物件(比如,我點了一張圖,另一個手指在外面圖的外面點下去)
//那麼就把這個之前那個觸控目標定為第一個觸控物件,並且把這個觸控(pointer)分配給最近新增的觸控目標
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.
//child view沒有消費觸控事件
if (mFirstTouchTarget == null) {
// No tuch targets so treat this as an ordinary view.
// child view沒有消費事件,把自己當做view來消費
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;
//遍歷TouchTargt樹.分發事件,如果我們已經分發給了新的TouchTarget那麼我們就不再分發給newTouchTarget
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
//是否讓child取消處理事件,如果為true,就會分發給child一個ACTION_CANCEL事件
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//派發事件
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
//cancelChild也就是說,派發給了當前child一個ACTION_CANCEL事件,
//那麼就移除這個child
if (cancelChild) {
//沒有父節點,也就是當前是第一個TouchTarget
//那麼就把頭去掉
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
//把下一個賦予父節點的上一個,這樣當前節點就被丟棄了
predecessor.next = next;
}
//回收記憶體
target.recycle();
//把下一個賦予現在
target = next;
//下面的兩行不執行了,因為我們已經做了連結串列的操作了。
//主要是我們不能執行predecessor=target,因為刪除本節點的話,父節點還是父節點
continue;
}
}
//如果沒有刪除本節點,那麼下一輪父節點就是當前節點,下一個節點也是下一輪的當前節點
predecessor = target;
target = next;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
//遇到了取消事件、或者是單點觸控下情況下手指離開,我們就要更新觸控的狀態
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
//如果是多點觸控下的手指擡起事件,就要根據idBit從TouchTarget中移除掉對應的Pointer(觸控點)
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
ViewGroup中的dispatchTransformedTouchEvent完整原始碼
dispatchTransformedTouchEvent的主要功能是呼叫childView的dispatchTouchEvent方法完成一輪的事件分發機制,如果dispatchTouchEvent返回true則表示子View消費了事件,false表示子類沒有消費事件,繼續事件分發;
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) {
int oldAction = event.getAction();
boolean handled;
if (!cancel && oldAction !=MotionEvent.ACTION_CANCEL) {
int oldPointerIdBits = event.getPointerIdBits();
int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
if (newPointerIdBits == 0) {
return false;
} else {
MotionEvent transformedEvent;
float offsetX;
float offsetY;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
//child為null時即沒有子View時直接呼叫父類View的dispatchTouchEvent()把自己當做view來消費 ;
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
offsetX = (float)(this.mScrollX - child.mLeft);
offsetY = (float)(this.mScrollY - child.mTop);
event.offsetLocation(offsetX, offsetY);
//子View不為空繼續呼叫dispatchTouchEvent向下分發;
handled = child.dispatchTouchEvent(event);
event.offsetLocation(-offsetX, -offsetY);
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
// newPointerIdBits != oldPointerIdBits時
if (child == null) {
//child為null時即沒有子View時直接呼叫父類View的dispatchTouchEvent()把自己當做view來消費 ;
handled = super.dispatchTouchEvent(transformedEvent);
} else {
offsetX = (float)(this.mScrollX - child.mLeft);
offsetY = (float)(this.mScrollY - child.mTop);
transformedEvent.offsetLocation(offsetX, offsetY);
if (!child.hasIdentityMatrix()) {
transformedEvent.transform(child.getInverseMatrix());
}
// 子View不為空繼續呼叫dispatchTouchEvent向下分發;
handled = child.dispatchTouchEvent(transformedEvent);
}
transformedEvent.recycle();
return handled;
}
} else {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
//child為null時即沒有子View時直接呼叫父類View的dispatchTouchEvent()把自己當做view來消費 ;
handled = super.dispatchTouchEvent(event);
} else {
//子View不為空繼續呼叫dispatchTouchEvent向下分發;
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
}
ViewGroup中的addTouchTarget完整原始碼
private ViewGroup.TouchTarget addTouchTarget(View child, int pointerIdBits) {
ViewGroup.TouchTarget target = ViewGroup.TouchTarget.obtain(child, pointerIdBits);
target.next = this.mFirstTouchTarget;
this.mFirstTouchTarget = target;
return target;
}
ViewGroup中的requestDisallowInterceptTouchEvent完整原始碼
用於設定ViewGroup攔截flage
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
if (disallowIntercept != ((this.mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
if (disallowIntercept) {
//重點:就是在這裡給mGroupFlags新增FLAG_DISALLOW_INTERCEPT不允許攔截事件標記位
this.mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
} else {
this.mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
if (this.mParent != null) {
this.mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
}
}
}
五、 View中事件分發View中的事件分發機制
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();
}
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//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;
}
}
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;
}
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;
}