View事件体系之事件的分发

事件的分发流程

Activity->window->ViewGroup(decor View)

dispathTouchEvent(属于Activity)

决定是否Activity要自己消费事件,首先将事件交由依附Activity的Window进行分发,如果View消费了事件,返回true,那么分发过程结束,如果所有的View都没有消费事件,那么Avtivity的onTouchEvent()会被调用.

decorView 分发过程

顶级View(ViewGroup)对View的分发包括几个过程:
点击事件到达-> 调用dispatchTouchEvent()->如果interecptTouchEvent()返回true,消费事件->a 否则 ->b

a.如果有onTouchListener(),则 onTouch()会被触发,否则onTouchEvent()会被调用,如果在onTouchEvent中设置了onClickListener,onCLick会被调用.

b.事件会传递给事件链上的子View,子View接收到事件调用dispatchTouchEvent().

事件链是一开始ViewGroup就会遍历所有的子View来判断哪些View可以接受到事件,主要根据 子View是否在播动画 和 点击坐标是否位于子View上.

interecptTouchEvent

并非每次都会调用,只有当 事件是ACTION_DOWN 且 mFirstTouchTarget != null(交由子View处理) 且 FLAG_DISALLOW_INTERCEPT 没被设置 时调用 onInterecptTouchEvent.

因为ACTION_DOWN基本上都是一个新的事件,这个时候肯定没有交由子View来处理,所以mFirstTouchTarget == null,再加上前面就有代码对FLAG_DISALLOW_INTERCEPT进行初始化,所以如果是ACTION_DOWN,onInterecptTouchEvent一定会被调用,但是decorView(Viewgroup)默认都不会拦截事件.因此子View不能影响decorView对ACTION_DOWN的处理.

如果 事件是ACTION_DOWN 且 mFirstTouchTarget != null(交由当前View处理) 都不成立,即是收到ACTION_MOVE,ACTION_UP且已经标记不拦截事件,交由子View处理了就直接交由子View,不再拦截.
当消费事件返回true,不消费返回false.

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public boolean dispatchTouchEvent(MotionEvent ev) {    ...    /**    见 上一节  `interecptTouchEvent`    */         // 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;         }       ...       /**       分发之核心,遍历所有的子View来判断哪些View可以接受到事件,主要根据 子View是否在播动画 和 点击坐标是否位于子View上.       */                     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);                         ...                         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();                 }         /**         如果所有的View都没有消费事件,那么ViewGroup将会自己消费事件;         否则继续处理后续事件(ACTION_UP,ACTION_MOVE)的分发,还有可能出现的取消点击(在屏幕上滑动离开目标View)         不再判断,直接将点击事件传给目标View         */         // 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;             }         } ... }

View对点击事件的处理

以上都是点击事件怎么从Activity->Window->decor View
但是大多数情况下,处理点击事件的是View.

具体过程已经写了注释:

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public boolean onTouchEvent(MotionEvent event) {     final float x = event.getX();     final float y = event.getY();     final int viewFlags = mViewFlags;     final int action = event.getAction();     /**     这里是View处于不可DISABLE的状态,但是仍然会消费事件.     前提是view是CLICKABLE 或者 LONG_CLICKABLE     */     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);     }     /**     如果View有设置代理,会执行mTouchDelegate.onTouchEvent(event)     */     if (mTouchDelegate != null) {         if (mTouchDelegate.onTouchEvent(event)) {             return true;         }     }     /**     如果View是CLICKABLE或者LONG_CLICKABLE,就消费事件.     */     if (((viewFlags & CLICKABLE) == CLICKABLE ||             (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||             (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {         switch (action) {             /**             如果`ACTION_UP`,说明一次点击事件结束,`performClick()`方法被调用,它调用它内部的`click()`方法.             */             case MotionEvent.ACTION_UP:              ...                             if (mPerformClick == null) {                                 mPerformClick = new PerformClick();                             }                             if (!post(mPerformClick)) {                                 performClick();                             }             ...                 break;             /**             如果是`ACTION_DOWN`的情况,考虑是不是滑动操作.如果是就进行滑动操作的初始化;             否则调用`setPressed()`来设置当前的按压状态->因为:             事件分发到这里就以及确定了哪个`View`消费了事件,这个时候就要把这个消息往回传,告诉高等级那些大人物们.             回传的起点自然就是当前所在的`view`的`onTouchEvent`->`dispatchSetPressed(pressed)`,             让整个view都知道事件消费情况,并且返回`result`告诉viewGroup             */             //ViewGroup#dispatchTransformedTouchEvent()              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;                     }             /**             而ViewGroup#dispatchTouchEvent()收到返回值是这样的             */             //ViewGroup#dispatchTouchEvent()              if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {                          ...                             mLastTouchDownX = ev.getX();                             mLastTouchDownY = ev.getY();                             newTouchTarget = addTouchTarget(child, idBitsToAssign);                             alreadyDispatchedToNewTouchTarget = true;                             break;                         }             /**             这是一个循环的一部分,这个循环遍历child(子View),用`dispatchTransformedTouchEvent()`进行分发;             如果分发未果,没有消费事件,就遍历下一个子View;             如果分发成功执行其内部操作,可以看到,已经分发成功,并获取到目标`View`.             */             case MotionEvent.ACTION_DOWN:                 ...                 // 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();                     }                   ...                 } else {                     // Not inside a scrolling container, so show the feedback right away                         /**                          * Sets the pressed state for this view and provides a touch coordinate for                          * animation hinting.                          *                          * @param pressed Pass true to set the View's internal state to "pressed",                          *            or false to reverts the View's internal state from a                          *            previously set "pressed" state.                          * @param x The x coordinate of the touch that caused the press                          * @param y The y coordinate of the touch that caused the press                          */                     setPressed(true, x, y);                     checkForLongClick(0);                 }                 break;                 /**                 撤销动作,算作没有消费事件                 */             case MotionEvent.ACTION_CANCEL:                 setPressed(false);                 removeTapCallback();                 removeLongPressCallback();               ...                 break;                 /**                 移动                 */             case MotionEvent.ACTION_MOVE:               ...                 break;         }         return true;     }     return false; }

事件分发-恶魔法则11条

1.同一序列事件是指从手指接触屏幕开始,到手指离开屏幕结束,中间产生的一系列以ACTION_DOWN开始,中间N个ACTION_MOVE,最后以ACTION_UP结束的一系列事件.

2.某个View一旦决定拦截事件(拦截了ACTION_DOWN),那么剩下的ACTION_MOVE & ACTION_UP都只能交由它处理,并且它的onInterceptTouchEvent()不再会被调用(其实如果是子View的话,decor View的也不会再被调用).

3.一个事件只能被一个View拦截消耗,因为后续不会再有拦截,也就没机会交给其它View处理.

4.某个View一旦开始处理事件,如果它不消耗ACTION_DOWN事件(onTouchEvent返回false)那么同一事件序列中的其它事件都不会再交由它处理, 会交由他们的父元素处理(Activity),既父元素的onTouchEvent会被调用.

5.如果View不消耗ACTION_DOWN以外的事件,这个点击事件会消失,父元素的onTouchEvent不会被调用,最后这些消失的点击事件会传给Activity处理.

6.ViewaGroup默认不拦截任何事件.

7.View没有onInterceptTouchEvent,事件传递给它后它的onTouchEvent就会被调用.

8.View的onTouchEvent默认消耗事件,除非它的CLICKABLE和LONG_CLICKABLE都为false.

9.View的ENABLE不影响事件的消费,只有CLICKABLE影响.

10.onClick会发生的前提是View是可点击的,并且收到了一系列事件(ACTION_DOWN->ACTION_UP),并且设置了监听(listener).

11.事件总是先传给父元素再分发给子View,可以通过requestDissallowInterceptTouchEvent来干预父元素除了ACTION_DOWN事件的分发.\

原文链接：http://www.apkbus.com/blog-705730-62507.html