/** \frameworks\base\core\java\android\app\Activity.java **/
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}
代碼很簡單,當是ACTION_DOWN事件時,會先調用onUserInteraction方法,該方法其實就是個Activity的空函數,可以在定義Activity繼承時進行Override,完成一些ACTION_DOWN事件分發前的處理工作;
/** \frameworks\base\core\java\android\app\Activity.java **/
public void onUserInteraction() {
}
可以看到重寫onUserInteraction方法並不會對MotionEvent的派發產生影響,但是每一個對ACTION_DOWN事件的派發都會調用onUserInteraction方法。
/** \frameworks\base\policy\src\com\android\internal\policy\impl\PhoneWindow.java**/
private DecorView mDecor;
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}
PhoneWindow繼續將事件傳遞給內部的DecorView;
/** \frameworks\base\policy\src\com\android\internal\policy\impl\PhoneWindow.java**/
private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {
public boolean superDispatchTouchEvent(MotionEvent event) {
return super.dispatchTouchEvent(event);
}
}
DecorView是PhoneWindow的子類,其會進一步調用super.dispatchTouchEvent(event),DecorView繼承FrameLayout,FrameLayout中並未實現dispatchTouchEvent方法;FameLayout繼承ViewGroup,則繼續調用ViewGroup的dispatchTouchEvent方法;即事件從Activity傳到Window進而傳遞到ViewGroup中;DecorView是頂層ViewGroup,可想而知,接下來的dispatch會根據View樹進行逐級派發事件。
3、ViewGroup#dispatchTouchEvent:(代碼較長,分段閱讀如下):
1)處理ACTION_DOWN事件:
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
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.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
ACTION_DOWN操作可以看做一個完整事件流程的起點,故在該系列動作開始時,會清理之前設置過狀態,其中cancelAndClearTouchTargets會將下面將會看到的mFirstTouchTarget變量置爲null;
2)判斷是否對事件進行攔截:
// Check for interception.
final boolean intercepted;
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;
}
可以看到不攔截情況包括有ACTION_DOWN事件,或者mFirstTouchTarget不爲null;
// First touch target in the linked list of touch targets.
private TouchTarget mFirstTouchTarget;
private static final class TouchTarget {
......
// The next target in the target list.
public TouchTarget next;
private TouchTarget() {
}
......
}
mFirstTouchTarget是TouchTarget對象,可以看到其其實最終形式一個鏈表。每一個ViewGroup中都包含一個 mFirstTouchTarget對象,其指向處理TouchEvent事件的下一個View,即該ViewGroup的子元素A如果成功處理了該TouchEvent事件,就會將mFirstTouchTarget指向A;
其實容易理解,這些都是針對於一個完整系列的操作事件而設計的;該事件以ACTION_DOWN事件爲開端,噹噹前事件爲ACTION_DOWN時,表示又是一個新的操作,所以將所有配置全部重置,尤其是將mFirstTouchTarget置爲null;此時不用管mFirstTouchTarget,因爲是ACTION_DOWN事件會就直接跳入到判斷是否攔截的代碼中。
而在接下來會看到,mFirstTouchTarget將會賦值,如果發生了攔截,mFirstTouchTarget將會置爲null,否則將指向下一個將要傳遞事件的子View;當系列操作中ACTION_MOVE或者ACTION_UP事件派發時,如果已經之前事件分發時已經發生了攔截,此時mFirstTouchTarget==null也就是mFirstTouchTarget!=null條件不成立,則會直接建立攔截,無需再次調用onInterceptTouchEvent;
所以有結論:若某個View一旦發生攔截,那麼這一個事件序列都只能由它來處理,並且它的onInterceptTouchEvent方法將不再會調用。
同時注意這裏有一個標記位FLAG_DISALLOW_INTERCEPT,由字面意思就可以看出,設置它就可以使得攔截無效(從代碼中可以看出,因爲會直接跳到intercepted爲false,即不攔截的情況。但注意,由於ACTION_DOWN的特殊性,其表示一個序列事件的起點,會對所有狀態,包括FLAG_DISALLOW_INTERCEPT標誌位進行重置無效化,所以設置FLAG_DISALLOW_INTERCEPT並不能攔截ACTION_DOWN事件,ACTION_DOWN事件的攔截只能發生在onInterceptTouchEvent的處理邏輯中。
假設在該層ViewGroup並不發生攔截,即intercepted爲false,ViewGroup會將事件分發給它的子View進行處理:
3)當未發生攔截,分發事件給子View:
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE)
{
.....
final int childrenCount = mChildrenCount; // 獲取子對象
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
.....
final View[] children = mChildren;
// 遍歷子View
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = customOrder
? getChildDrawingOrder(childrenCount, i) : i;
final View child = (preorderedList == null)
? children[childIndex] : preorderedList.get(childIndex);
.....
/** 這裏是重要的處理函數 ***/
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(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();
}
}
上面主要是對事件向子View轉發的處理;系統如果採用將事件全部轉發,也就是廣播給所有子View,然後在子View中去判斷自己是否應當處理該event,這樣效率顯然是相當低的。因此係統採取的做法是先進行判斷,遍歷所有子View,判斷適合接收該event的子View,然後將該事件傳遞給它。上面的代碼中完成就是這樣的問題。
主要涉及到的函數爲canViewReceivePointerEvents和isTransformedTouchPointInView,可以看到如果兩個判斷均通過的話,該child即是所要尋找的結果,會調用dispatchTransformedTouchEvent方法將事件傳遞給它;
I) canViewReceivePointerEvents方法是判斷該View是否能夠該收該event,源碼如下:
private static boolean canViewReceivePointerEvents(View child) {
return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null;
}
可以看到當child的狀態爲VISIBLE狀態,或者child當前在播放動畫時,此時該View是可以接受該event的;
II)isTransformedTouchPointInView方法是判斷點擊事件的座標是否在child的區域範圍內:
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;
}
III)當兩個條件都滿足,即調用dispatchTransformedTouchEvent方法將事件傳遞給child:
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
....
// Perform any necessary transformations and dispatch.
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
......
handled = child.dispatchTouchEvent(transformedEvent);
}
return handled;
}
如果child爲null,表示無子View或者改事件點擊範圍內沒有滿足條件的子View,則調用ViewGroup的父類View中的dispatchTouchEvent函數來處理event;否則,調用child的方法繼續下一輪事件派發;
IV)在dispatchTransformedTouchEvent函數結果值爲true的情況下,會繼續往下執行,執行的主要代碼如下:
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
即如果child子元素的dispatchTouchEvent返回結果爲true時,會執行addTouchTarget,
private TouchTarget addTouchTarget(View child, int pointerIdBits) {
TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}
這裏完成對mFirstTouchTarget的初始化。
4、View對事件的處理過程:
由前面可以看到,當發生攔截或者事件分發到最底層的View時,事件會交給View的dispatchTouchEvent方法進行處理;
View#dispatchTouchEvent:
public boolean dispatchTouchEvent(MotionEvent event) {
....
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
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;
}
}
......
}
這裏是對Touch事件處理的主要邏輯,由View機制深入學習(三)
View中的消息傳遞及InputManagerService 知ListenerInfo是對View註冊的一系列Listener的管理者,比如OnClickListener;這裏和上文中的邏輯相同,若是View註冊了onTouchListener,則先調用onTouchListener的onTouch方法處理事件,若onTouch方法返回true,則攔截事件,不再繼續向下處理;若onTouch返回false,則會繼續調用View中的onTouchEvent方法處理事件。
View#onTouchEvent:
I、狀態爲DISABLED的View相應點擊事件
if ((viewFlags & ENABLED_MASK) == DISABLED) {
if (action == 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)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
可以看到當View爲DISABLED狀態時,依然會消耗點擊事件,只不過是不做處理而已。View的enable屬性是不影響View中onTouchEvent默認的返回值的,即使是DIABLED狀態,只要其clickable或者long_clickable爲true,就會返回true,消耗該點擊事件。
II、主要的事務處理邏輯:
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
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 (!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)) {
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;
View會針對TouchEvent事件類型的不同進行分別處理,這裏以ACTION_UP爲例,可以看到最核心的響應就是觸發performClick()方法:
III、View#performClick:
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);
return result;
}
可以看到OnClickListener的處理邏輯就在這裏,如果View註冊了 OnClickListener,在ACTION_UP事件到達該View時,會最終觸發performClick方法,該方法中進而調用OnClickListener的onClick函數,故而在日常使用中則是重寫onClick方法來實現點擊的響應,並且onClick(View
view)這裏將this作參數傳遞進來,因此onClick中的view即代表被click的組件View。