事件传递
当一个点击事件发生时,事件最先传递给当前Activity,由Activity 的 dispatchTouchEvent 来进行事件分发,具体的工作是由Activity 内部的Window 来完成(即PhoneWindow),Window 会将事件传递给 decor view, decor view 一般就是当前的底层容器(即setContent 所设置的 View 的父容器),通过 Activity.getWindow.getDecorView() 获取,通过ViewGroup 的事件分发,传递到最终的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)) {//事件开始交给Activity 所附属的 Window 进行分发 return true; } return onTouchEvent(ev); }
首先事件开始交给Activity 所附属的 Window 进行分发,如果返回 true ,整个事件循环就结束了,返回false 意味着事件没人处理,所有 View 的onTouchEvent 都返回了 false,则 Activity 的 onTouchEvent 就会被调用
由于Window 是抽象类,且Window 的 superDispatchTouchEvent 方法也是抽象方法,故需找到Window 的唯一实现类 PhoneWindow
PhoneWindow 源码:
@Override public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); }DecorView
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; }
这个DecorView 就是我们视图的根View,它里面有两个子View,一个TitleView,一个ContentView,这个ContentView 就是我们在Activity 中通过 setContentView 所设置的 View,由于 DecorView 继承自 FrameLayout ,且是父View,所以事件最终会传递给View。
顶级View 对点击事件的分发过程
点击事件到达顶级View 之后,会调用ViewGroup 的 dispatchTouchEvent 方法,然后的逻辑如下:如果顶级ViewGroup 拦截事件即 onInterceptTouchEvent 返回 true,则事件由 ViewGroup 处理,此时如果 ViewGroup 的 mOnTouchListener 被设置,则 onTouch 会被调用,否则 onTouchEvent 会被调用,即如果给控件设置了 onTouchListener 监听,则onTouch 会屏蔽掉 onTouchEvent 。在 onTouchEvent 中,如果设置了 mOnClickListener ,则onClick 会被调用。
即 onTouchListener 的优先级大于 onTouchEvent 大于 onClick
如果顶级ViewGroup 不拦截事件,则事件会传递给它所在的点击事件链上的子 View,这时子 View 的 dispatchTouchEvent 会被调用,此时事件已经从顶级View 传递给了下一层View ,接下来的传递过程和顶级 View 是一致的,如此循环,完成整个事件的分发
@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) {//重置标记位 // 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;//检查是否拦截事件的标志位 //通过 DOWN 事件和 mFirstTouchTarget 是否为空 判断是否拦截当前事件,mFirstTouchTarget在ViewGroup 的子View 成功消费事件时赋值, if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; //通过disallowIntercept 来判断是否拦截当前事件,其可通过requestDisallowInterceptTouchEvent 来设置,默认为 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;//检查是否拦截事件的标志位 //通过 DOWN 事件和 mFirstTouchTarget 是否为空 判断是否拦截当前事件,mFirstTouchTarget在ViewGroup 的子View 成功消费事件时赋值, if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; //通过disallowIntercept 来判断是否拦截当前事件,其可通过requestDisallowInterceptTouchEvent 来设置,默认为 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; }
从上可知,ViewGroup 在两种情况下会判断是否拦截当前事件:
事件类型为 DOWN 或者
mFirstTouchTarget != null,
当事件被顶级View 的子 View 消费时,
mFirstTouchTarget 会被赋值并指向子 View;
如果事件被拦截,则
mFirstTouchTarget != null 就不会成立,当ACTION_MOVE、ACTION_UP 到来时,判断条件不成立,导致ViewGroup 的 onInterceptTouchEvent(ev)方法就不会被调用, intercepted = true; 并且同一序列(即从down-move-move...up 的一系列事件)中的其他事件都会默认交给这个View 处理
FLAG_DISALLOW_INTERCEPT 标记位:可通过 requestDisallowInterceptTouchEvent 方法来设置,一般用于子View 中,其默认值为 false;由上述代码可以看出,当该标记位为 true 时,ViewGroup 的 onInterceptTouchEvent(ev)方法就不会被调用,intercepted = false;ViewGroup 将无法拦截除了 ACTION_DOWN 事件外的其它事件,其原因如下源码所示:
// 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 }
从源码中可知,当ViewGroup 在分发事件时,如果是ACTION_DOWN 事件,则会重置 FLAG_DISALLOW_INTERCEPT 标记位,导致子View 中设置的这个标记位无效,即每一个ACTION_DOWN 都会先重置标记位,在View 的ACTION_DOWN 事件中调用requestDisallowInterceptTouchEvent 毫无意义
FLAG_DISALLOW_INTERCEPT 一旦设置后,ViewGroup 将无法拦截除了 ACTION_DOWN 事件外的其他点击事件,当面对 ACTION_DOWN 事件时, ViewGroup 总会调用自己的 onInterceptTouchEvent 方法询问自己是否要拦截事件,在ViewGroup 中会在ACTION_DOWN 事件到来时做重置状态的操作,在resetTouchState 方法中会对 FLAG_DISALLOW_INTERCEPT 进行重置,所以 View 调用
requestDisallowInterceptTouchEvent 方法并不能影响 ViewGroup 对 ACTION_DOWN 事件的处理
ViewGroup 的事件分发源码
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; } //判断子元素是否在播放动画和点击事件是否落在子元素区域 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)) {//根据是否有子View 来分发事件 // 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; }dispatchTransformedTouchEvent 源码
/** * 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,则mFirstTouchTarget 会被赋值并跳出循环。
addTouchTarget(child, idBitsToAssign)源码
/** * 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; }
这里完成了mFirstTouchTarget 的赋值并终止了对子元素的便利,如果子元素的 dispatchTouchEvent 返回false,则ViewGroup 会把事件分发给下一个子元素,直到遍历完所有的子元素
如果mFirstTouchTarget 为null ,即ViewGroup 没有子元素或者子元素在 onTouchEvent 中返回了 false,此时就会调用下面的代码
// 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); }
注意这里第三个参数chile 为 null,从前面的dispatchTransformedTouchEvent 中可知,他会调用super.dispatchTouchEvent(event);方法,这里就转到了View 的 dispatchTouchEvent 方法,即点击事件开始交由View 来处理
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; }从源码中可看出, onInterceptTouchEvent 默认返回 false,即ViewGroup 默认不拦截认可事件
View 的 diapatchTouchEvent 方法源码:
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; //判断是否设置 onTouchListener 监听 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; }
从上述源码中可看出,如果View 设置了 onTouchListener ,则它的 onTouch方法会调用,如果onTouch 方法返回 true,则onTouchEvent 方法就不会被调用,可见OnTouchListener 的优先级高于 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 处于不可点击状态下的点击事件的处理过程 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 有一个为true,就会消耗这个事件,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();//点击事件消费的地方 } 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; }
当 ACTION_UP 事件发生时,会触发 performClick 方法,如果View 设置了 OnClickListener ,则performClick 会内部调用它的 onClick 方法
performClick 源码:
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 设置了 OnClickListener,则performClick 方法内部会调用它的 onClick 方法
View 的LONG_CLICKABLE 属性默认为false,而CLICKABLE 属性是否为 false和具体的View 有关,具体说就是可点击的View 的CLICKABLE 为true ,不可点击的View CLICKABLE 为false,可通过setOnLongClickListener 和 改变View 的LONG_CLICKABLE 和 CLICKABLE 属性,会分别将LONG_CLICKABLE 和 CLICKABLE 自动置为 trues
public void setOnClickListener(@Nullable OnClickListener l) { if (!isClickable()) { setClickable(true); } getListenerInfo().mOnClickListener = l; }setOnLongClickListener
public void setOnLongClickListener(@Nullable OnLongClickListener l) { if (!isLongClickable()) { setLongClickable(true); } getListenerInfo().mOnLongClickListener = l; }
结论:
- 同一个事件序列是指从手指接触屏幕的那一刻起,直到手指离开屏幕的那一刻结束所产生的一系列事件。这个事件序列以 down事件开始,中间包含一系列 move 事件,最终以 up 事件结束
- 正常情况下,一个事件序列只能被一个View 拦截且消费
- 某个 View 一旦决定拦截事件,则这一个事件序列都会交由它来处理,且它的 onInterceptTouchEvent 不会再被调用,从ViewGroup 源码事件的拦截判断中可得出
- 某个View 一旦开始处理事件,如果它不消耗 ACTION_DOWN 事件(即 onTouchEvent 返回了 false),则统一事件序列的其他事件都不会再交给他来处理,并且事件将重新交由它的父元素去处理,即父元素的 onTouchEvent 会被调用,从ViewGroup 源码事件的拦截判断中可得出
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ViewGroup 默认不拦截任何事件,Android 源码中 ViewGroup 的 onInterceptTouchEvent 方法默认返回 false
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View 没有 onInterceptTouchEvent 方法,一旦有点击事件传递给它,则它的 onTouchEvent 方法就会被调用
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View 的 onTouchEvent 方法默认返回 true ,除非他是不可点击的
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View 的 enable 属性不影响 onTouchEvent 的默认返回值。哪怕一个View 是 disable 状态,只要他的 clickable 或者 longClickable 有一个为 true,则它的onTouchEvent 就返回 true
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onClick 会发生的前提是当前View 可点击,且收到了 down 和 up 事件
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事件的传递是由外向内的,即事件总是先传递到父元素,然后由父元素分发给子 View,通过调用 requestDisableIntercepTouchEvent 可在子元素中干预父元素的事件分发过程,但 ACTION_DOWN事件除外