事件傳遞
當一個點擊事件發生時，事件最先傳遞給當前Activity，由Activity 的 dispatchTouchEvent 來進行事件分發，具體的工作是由Activity 內部的Window 來完成(即PhoneWindow)，Window 會將事件傳遞給 decor view， decor view 一般就是當前的底層容器（即setContent 所設置的 View 的父容器），通過 Activity.getWindow.getDecorView() 獲取，通過ViewGroup 的事件分發，傳遞到最終的View 上
Activity 的 dispatchTouchEvent
/**
* 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)) {//事件開始交給Activity 所附屬的 Window 進行分發
return true;
}
return onTouchEvent(ev);
} 首先事件開始交給Activity 所附屬的 Window 進行分發，如果返回 true ，整個事件循環就結束了，返回false 意味着事件沒人處理，所有 View 的onTouchEvent 都返回了 false，則 Activity 的 onTouchEvent 就會被調用
由於Window 是抽象類，且Window 的 superDispatchTouchEvent 方法也是抽象方法，故需找到Window 的唯一實現類 PhoneWindow
PhoneWindow 源碼：
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
return mDecor.superDispatchTouchEvent(event);
}public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
// This is the top-level view of the window, containing the window decor.
private DecorView mDecor;
@Override
public final View getDecorView() {
if (mDecor == null || mForceDecorInstall) {
installDecor();
}
return mDecor;
} 這個DecorView 就是我們視圖的根View，它裏面有兩個子View，一個TitleView，一個ContentView，這個ContentView 就是我們在Activity 中通過 setContentView 所設置的 View，由於 DecorView 繼承自 FrameLayout ，且是父View，所以事件最終會傳遞給View。
頂級View 對點擊事件的分發過程
點擊事件到達頂級View 之後，會調用ViewGroup 的 dispatchTouchEvent 方法，然後的邏輯如下：如果頂級ViewGroup 攔截事件即 onInterceptTouchEvent 返回 true，則事件由 ViewGroup 處理，此時如果 ViewGroup 的 mOnTouchListener 被設置，則 onTouch 會被調用，否則 onTouchEvent 會被調用，即如果給控件設置了 onTouchListener 監聽，則onTouch 會屏蔽掉 onTouchEvent 。在 onTouchEvent 中，如果設置了 mOnClickListener ，則onClick 會被調用。
即 onTouchListener 的優先級大於 onTouchEvent 大於 onClick
如果頂級ViewGroup 不攔截事件，則事件會傳遞給它所在的點擊事件鏈上的子 View，這時子 View 的 dispatchTouchEvent 會被調用，此時事件已經從頂級View 傳遞給了下一層View ，接下來的傳遞過程和頂級 View 是一致的，如此循環，完成整個事件的分發
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
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.
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {//重置標記位
// 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.
final boolean intercepted;//檢查是否攔截事件的標誌位
//通過 DOWN 事件和 mFirstTouchTarget 是否爲空 判斷是否攔截當前事件，mFirstTouchTarget在ViewGroup 的子View 成功消費事件時賦值，
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
//通過disallowIntercept 來判斷是否攔截當前事件，其可通過requestDisallowInterceptTouchEvent 來設置，默認爲 false
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;
}
// 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) {
// If the event is targeting accessiiblity 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--) {
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) {
// No touch targets so treat this as an ordinary view.
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;
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;
} final boolean intercepted;//檢查是否攔截事件的標誌位
//通過 DOWN 事件和 mFirstTouchTarget 是否爲空 判斷是否攔截當前事件，mFirstTouchTarget在ViewGroup 的子View 成功消費事件時賦值，
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
//通過disallowIntercept 來判斷是否攔截當前事件，其可通過requestDisallowInterceptTouchEvent 來設置，默認爲 false
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;
}從上可知，ViewGroup 在兩種情況下會判斷是否攔截當前事件：事件類型爲 DOWN 或者 mFirstTouchTarget != null，
當事件被頂級View 的子 View 消費時，mFirstTouchTarget 會被賦值並指向子 View；如果事件被攔截，則mFirstTouchTarget != null 就不會成立，當ACTION_MOVE、ACTION_UP 到來時，判斷條件不成立，導致ViewGroup 的 onInterceptTouchEvent(ev)方法就不會被調用， intercepted = true; 並且同一序列（即從down-move-move...up 的一系列事件）中的其他事件都會默認交給這個View 處理
FLAG_DISALLOW_INTERCEPT 標記位：可通過 requestDisallowInterceptTouchEvent 方法來設置，一般用於子View 中，其默認值爲 false；由上述代碼可以看出，當該標記位爲 true 時，ViewGroup 的 onInterceptTouchEvent(ev)方法就不會被調用，intercepted = false;ViewGroup 將無法攔截除了 ACTION_DOWN 事件外的其它事件，其原因如下源碼所示：
// 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();//重置FLAG_DISALLOW_INTERCEPT
} 從源碼中可知，當ViewGroup 在分發事件時，如果是ACTION_DOWN 事件，則會重置 FLAG_DISALLOW_INTERCEPT 標記位，導致子View 中設置的這個標記位無效，即每一個ACTION_DOWN 都會先重置標記位，在View 的ACTION_DOWN 事件中調用requestDisallowInterceptTouchEvent 毫無意義
FLAG_DISALLOW_INTERCEPT 一旦設置後，ViewGroup 將無法攔截除了 ACTION_DOWN 事件外的其他點擊事件，當面對 ACTION_DOWN 事件時， ViewGroup 總會調用自己的 onInterceptTouchEvent 方法詢問自己是否要攔截事件，在ViewGroup 中會在ACTION_DOWN 事件到來時做重置狀態的操作，在resetTouchState 方法中會對 FLAG_DISALLOW_INTERCEPT 進行重置，所以 View 調用
requestDisallowInterceptTouchEvent 方法並不能影響 ViewGroup 對 ACTION_DOWN 事件的處理
ViewGroup 的事件分發源碼
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;
}
//判斷子元素是否在播放動畫和點擊事件是否落在子元素區域
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)) {//根據是否有子View 來分發事件
// 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;
} /**
* Transforms a motion event into the coordinate space of a particular child view,
* filters out irrelevant pointer ids, and overrides its action if necessary.
* If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
*/
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;
}如果子元素的 dispatchTouchEvent 返回 true，則mFirstTouchTarget 會被賦值並跳出循環。
addTouchTarget(child, idBitsToAssign)源碼
/**
* Adds a touch target for specified child to the beginning of the list.
* Assumes the target child is not already present.
*/
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
mFirstTouchTarget = target;
return target;
}這裏完成了mFirstTouchTarget 的賦值並終止了對子元素的便利，如果子元素的 dispatchTouchEvent 返回false，則ViewGroup 會把事件分發給下一個子元素，直到遍歷完所有的子元素
如果mFirstTouchTarget 爲null ，即ViewGroup 沒有子元素或者子元素在 onTouchEvent 中返回了 false，此時就會調用下面的代碼
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
}注意這裏第三個參數chile 爲 null，從前面的dispatchTransformedTouchEvent 中可知，他會調用super.dispatchTouchEvent(event);方法，這裏就轉到了View 的 dispatchTouchEvent 方法，即點擊事件開始交由View 來處理
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;
}View 的 diapatchTouchEvent 方法源碼：
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;
//判斷是否設置 onTouchListener 監聽
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;
} 從上述源碼中可看出，如果View 設置了 onTouchListener ，則它的 onTouch方法會調用，如果onTouch 方法返回 true，則onTouchEvent 方法就不會被調用，可見OnTouchListener 的優先級高於 onTouchEvent
onTouchEvent
public boolean onTouchEvent(MotionEvent event) {
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;
//View 處於不可點擊狀態下的點擊事件的處理過程
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 doesn't respond to them.
return clickable;//返回clickable
}
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
//只要View 的 CLICKABLE 和LONG_CLICKABLE 有一個爲true，就會消耗這個事件，即onTouchEvent 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 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();//點擊事件消費的地方
}
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;
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 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, 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;//onTouchEvent 返回 true
}
return false;
}當 ACTION_UP 事件發生時，會觸發 performClick 方法，如果View 設置了 OnClickListener ，則performClick 會內部調用它的 onClick 方法
performClick 源碼：
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;
}由上可知，如果 View 設置了 OnClickListener，則performClick 方法內部會調用它的 onClick 方法
View 的LONG_CLICKABLE 屬性默認爲false，而CLICKABLE 屬性是否爲 false和具體的View 有關，具體說就是可點擊的View 的CLICKABLE 爲true ，不可點擊的View CLICKABLE 爲false，可通過setOnLongClickListener 和 改變View 的LONG_CLICKABLE 和 CLICKABLE 屬性，會分別將LONG_CLICKABLE 和 CLICKABLE 自動置爲 trues
public void setOnClickListener(@Nullable OnClickListener l) {
if (!isClickable()) {
setClickable(true);
}
getListenerInfo().mOnClickListener = l;
} public void setOnLongClickListener(@Nullable OnLongClickListener l) {
if (!isLongClickable()) {
setLongClickable(true);
}
getListenerInfo().mOnLongClickListener = l;
}結論：
- 同一個事件序列是指從手指接觸屏幕的那一刻起，直到手指離開屏幕的那一刻結束所產生的一系列事件。這個事件序列以 down事件開始，中間包含一系列 move 事件，最終以 up 事件結束
- 正常情況下，一個事件序列只能被一個View 攔截且消費
- 某個 View 一旦決定攔截事件，則這一個事件序列都會交由它來處理，且它的 onInterceptTouchEvent 不會再被調用，從ViewGroup 源碼事件的攔截判斷中可得出
- 某個View 一旦開始處理事件，如果它不消耗 ACTION_DOWN 事件(即 onTouchEvent 返回了 false)，則統一事件序列的其他事件都不會再交給他來處理，並且事件將重新交由它的父元素去處理，即父元素的 onTouchEvent 會被調用，從ViewGroup 源碼事件的攔截判斷中可得出
- ViewGroup 默認不攔截任何事件，Android 源碼中 ViewGroup 的 onInterceptTouchEvent 方法默認返回 false
- View 沒有 onInterceptTouchEvent 方法，一旦有點擊事件傳遞給它，則它的 onTouchEvent 方法就會被調用
- View 的 onTouchEvent 方法默認返回 true ，除非他是不可點擊的
- View 的 enable 屬性不影響 onTouchEvent 的默認返回值。哪怕一個View 是 disable 狀態，只要他的 clickable 或者 longClickable 有一個爲 true，則它的onTouchEvent 就返回 true
- onClick 會發生的前提是當前View 可點擊，且收到了 down 和 up 事件
- 事件的傳遞是由外向內的，即事件總是先傳遞到父元素，然後由父元素分發給子 View，通過調用 requestDisableIntercepTouchEvent 可在子元素中干預父元素的事件分發過程，但 ACTION_DOWN事件除外