Android事件分发机制（二）

当ViewGroup不拦截事件时，事件将会向子View传递，那到底是怎样把事件传递到子View的呢？接下来将分析这个流程，先看代码

ViewGroup事件分发

final View[] children = mChildren;for (int i = childrenCount - 1; i >= 0; i--) {    final int childIndex = getAndVerifyPreorderedIndex(            childrenCount, i, customOrder);//得到View的索引    final View child = getAndVerifyPreorderedView(            preorderedList, children, childIndex);//／／得到View    //判断该View是否可以接收事件，而且点击的左边在此View内    if (!canViewReceivePointerEvents(child)            || !isTransformedTouchPointInView(x, y, child, null)) {        ev.setTargetAccessibilityFocus(false);        continue;    }    //........................    newTouchTarget = getTouchTarget(child);//得到了Touch的子View    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);    //下面调用了子View的dispatchTouchEvent    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;    }}

上面代码的主要逻辑大概是，for循环遍历所有的view，找到点击坐标所在区域的子View且这个View可以被点击，就将事件交给它处理，canViewReceivePointerEvents(child)方法可以判断View是否允许被点击。
接下来会调用

dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)

此方法就是调用了子View的dispatchTouchEvent，看代码

if (child == null) {    handled = super.dispatchTouchEvent(event);} else {    handled = child.dispatchTouchEvent(event);}

此时如果子View的dispatchTouchEvent返回true，会执行下面的代码，看到了mFirstTouchTarget被赋值，同时跳出了for循环。

newTouchTarget = addTouchTarget(child, idBitsToAssign);alreadyDispatchedToNewTouchTarget = true;break;/** * 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;}

如果遍历完所有的子元素后事件都没有被处理，有两种情况：ViewGroup没有子View或者子View处理了点击事件，但是dispatchTouchEvent返回了false，看代码

if (mFirstTouchTarget == null) {    // No touch targets so treat this as an ordinary view.    handled = dispatchTransformedTouchEvent(ev, canceled, null,            TouchTarget.ALL_POINTER_IDS);} else {｝

此时mFirstTouchTarget为空，会调用dispatchTransformedTouchEvent上面分析过此方法最终会调用
handled = super.dispatchTouchEvent(event);
因为ViewGroup的是继承子View，所以会调用View的dispatchTouchEvent，点击事件交给了View处理。

View的事件处理

根据上面的分析可以得知事件分发到了View的dispatchTouchEvent方法内，下面看代码。

if (onFilterTouchEventForSecurity(event)) {    if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {        result = true;    }    //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;    }}

可以看到会先判断是否设置了onTouchListener，如果设置了并且onTouchListener的onTouch方法返回了true，此时result＝true，不会再执行onTouchEvent方法，可以得出结论 onTouchListener的优先级高于onTouchEvent，这样做的好处是可以在外界处理点击事件。

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);}

从上面的注释可以知道，当一个View为不可用状态时，仍然会消费事件只是没有响应（没有执行performClick）。
接下来看onTouchEvent的ACTION_UP的事件处理

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();                        }                    }                }            break;      return true；    }

可以看到View的CLICKABLE和 LONG_CLICKABDLE有一个为true，就会消费点击事件，如果设置了点击事件performClick会触发onClickListener。
View的LONG_CLICKABLE默认为false，CLICKABLE属性根据默认值和具体的View有关，例如Button是可点击的为true，TextView不可以点击的通过
seOnClickListener会讲CLICKABLE改成true。
到此Android事件分发机制就完啦。