Android事件分发机制示例分析

public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: break; case MotionEvent.ACTION_MOVE: break; case MotionEvent.ACTION_UP: break; case MotionEvent.ACTION_CANCEL: break; } return true; }

 public boolean dispatchTouchEvent(MotionEvent ev) { if (ev.getAction() == MotionEvent.ACTION_DOWN) { onUserInteraction(); } if (getWindow().superDispatchTouchEvent(ev)) { return true; } return onTouchEvent(ev); }

 @Override public boolean superDispatchTouchEvent(MotionEvent event) { return mDecor.superDispatchTouchEvent(event); }

public boolean superDispatchTouchEvent(MotionEvent event) { return super.dispatchTouchEvent(event); }

public class ViewGroup { @Override public boolean dispatchTouchEvent(MotionEvent ev) { boolean handled = false; final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; // Check for interception. //按下后，第一次调用时actionMasked=down，mFirstTouchTarget=null //一直按着 actionMasked=move, 如果mFirstTouchTarget！=null说明有子view处理了touch事件 final boolean intercepted; if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { //调用子类复写的方法 如果为true表示拦截，false表示不拦截 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. //如果没有子view处理touch事件，并且不是第一次按下的down事件，group会对touch事件进行拦截 intercepted = true; } TouchTarget newTouchTarget = null; //第一次按下时，判断view是否处理事件的标志 boolean alreadyDispatchedToNewTouchTarget = false; //如果不拦截，则进入事件分发 if (!canceled && !intercepted) { //注意，只有ACTION_DOWN时才会遍历子View if (actionMasked == MotionEvent.ACTION_DOWN || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { final int childrenCount = mChildrenCount; if (newTouchTarget == null && childrenCount != 0) { final ArrayList preorderedList = buildTouchDispatchChildList(); final View[] children = mChildren; //开始遍历子view for (int i = childrenCount - 1; i >= 0; i--) { final View child = getAndVerifyPreorderedView( preorderedList, children, childIndex); //isTransformedTouchPointInView 通过比对坐标，来判断事件是否落在了child上， // true是，false不是 if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { ev.setTargetAccessibilityFocus(false); // 如果事件没有落在child上，则跳过此次循环，执行下一次循环 continue; } //通过遍历TouchTarget链表查找TouchTarget，如果找到了，则break跳出循环 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; } //第一次进来newTouchTarget==null，进入下面的逻辑 //如果dispatchTransformedTouchEvent 返回true，表示子view对事件进行了处理，则跳出此循环， // 不会再向子view进行分发 if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { // Child wants to receive touch within its bounds. //将child缓存到TouchTarget的链表中 newTouchTarget = addTouchTarget(child, idBitsToAssign); //注意这个标志位，true，下面的逻辑会用到 alreadyDispatchedToNewTouchTarget = true; break; } } if (preorderedList != null) preorderedList.clear(); } } } // Dispatch to touch targets. //ACTION_DOWN和ACTION_MOVE 的时都会执行下面逻辑 //mFirstTouchTarget==null 说明没有子View处理touch事件，dispatchTransformedTouchEvent的第三个参数为null。 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. //对 TouchTarget 链表进行遍历，TouchTarget里缓存了处理事件的view， //一次完整事件，move会调用多次，所以在ACTION_DOWN时找到的对应的view，缓存起来， // 而不是每次都遍历ViewGroup的子View，这样太损坏性能 TouchTarget target = mFirstTouchTarget; //开始对链表进行遍历，为啥是一个链表呢，这是为了进行多点触摸，会有多个view响应触摸事件。 while (target != null) { final TouchTarget next = target.next; //alreadyDispatchedToNewTouchTarget ==true ，并且缓存的target和newTouchTarget是同一个 //直接将handled置为true，防止ACTION_DOWN时dispatchTransformedTouchEvent方法重复调用 if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) { handled = true; } } target = next; } } //将handled 返回dispatchTouchEvent的调用者。 return handled; } /** * Gets the touch target for specified child view. * Returns null if not found. * 通过遍历TouchTarget 链表，找到touch target */ private TouchTarget getTouchTarget(@NonNull View child) { for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) { if (target.child == child) { return target; } } return null; } /** * Adds a touch target for specified child to the beginning of the list. * Assumes the target child is not already present. * 将TouchTarget和view进行关联，并且把这个TouchTarget放在链表的头部 */ private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) { final TouchTarget target = TouchTarget.obtain(child, pointerIdBits); target.next = mFirstTouchTarget; mFirstTouchTarget = target; return target; } private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) { final boolean handled; // 只看最关键的两行代码 if (child == null) { //如果child为null，没有子view处理touch事件，则调用父类View的dispatchTouchEvent。 handled = super.dispatchTouchEvent(transformedEvent); } else { //如果child不为空，则调用child view 的dispatchTouchEvent //这行代码很关键，如果child是ViewGroup则继续在ViewGoup的进行事件分发，这会是一个递归调用 //如果child 是一个View，则调用View的dispatchTouchEvent，进行事件的分发。 handled = child.dispatchTouchEvent(transformedEvent); } //以上两行代码最终会调用到View的dispatchTouchEvent方法。 return handled; } }

public class View { public boolean dispatchTouchEvent(MotionEvent ev) { boolean result = false; ListenerInfo li = mListenerInfo; //如果view设置了mOnTouchListener，先调用mOnTouchListener.onTouch， //如果返回true，则表示消费了此事件，不在向下传递，为啥这样说？那是因为，通过他的返回值，进行了逻辑判断 if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { result = true; } //如果result为false，则调用View.onTouchEvent方法 if (!result && onTouchEvent(event)) { result = true; } return result; } public boolean onTouchEvent(MotionEvent event) { switch (action) { case MotionEvent.ACTION_UP: if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { //调用performClick mOnClickListener.onClick()方法 performClickInternal(); } break; case MotionEvent.ACTION_DOWN: break; case MotionEvent.ACTION_CANCEL: break; case MotionEvent.ACTION_MOVE: break; } return false; } 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; } return result; } }