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  • Android事件分发机制浅析(2)

    本文来自网易云社区

    作者:孙有军


    上面的两次执行中每次都调用了onInterceptTouchEvent事件,这个到底又是啥?我们去看看他的返回值是什么?

    public boolean onInterceptTouchEvent(MotionEvent ev) 
    {    
    return false;
    }

    可以看到默认返回false,注释长的吓人,那我们就来改写一下他的返回值,这个函数是ViewGroup才有的,说明与布局容器有关.        round 3

    我们将Layout的onInterceptTouchEvent的返回值改为true。重新执行。执行顺序如下:

    05-05 14:59:17.829 15157-15157/com.sunny.event E/Event: Layout    dispatchTouchEvent ACTION_DOWN05-05 14:59:17.830 15157-15157/com.sunny.event E/Event: Layout    onInterceptTouchEvent ACTION_DOWN05-05 14:59:17.830 15157-15157/com.sunny.event E/Event: Layout    onTouchEvent ACTION_DOWN

    从日志可以发现,只有最外层的控件能够执行事件,TextView已经收不到任何事件。

    小结

    父控件onInterceptTouchEvent返回true会拦截子控件的事件

    追根溯源

    我们从代码的层面来看看他是怎么执行的,当屏幕接收到点击事件时会首先传递到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)) {        return true;
        }    return onTouchEvent(ev);
    }

    在这里执行了三步,

    1. 第一告诉用户ACTION_DOWN,用户可以复写onUserInteraction来处理点击开始

    2. 调用了getWindow().superDispatchTouchEvent(ev),这里的getWindow得到是PhoneWindow对象,因此执行的PhoneWindow的superDispatchTouchEvent函数,

    3. 调用了Activity的onTouchEvent事件

     PhoneWindow的superDispatchTouchEvent又调用了DecorView的superDispatchTouchEvent函数,每一个Activity都有一个PhoneWindow,每一个PhoneWindow都有一个DecorView,DecoView继承自FrameLayout,这里又调用了super.dispatchTouchEvent(event),FrameLayout里面是没有改函数的,所以最终执行的是ViewGroup的dispatchTouchEvent函数。

    这里我们先穿插一点界面的知识,以我测试手机为例,DecorView中有两个child,分别是ViewStub和LinerLayout,LinerLayout中又包含了FrameLayout,FrameLayout中包含了一个ActionBarOverlayLayout,ActionBarOverlayLayout里又包含了两个child,分别是ActionBarContainer与ContentFrameLayout。

    接下来我们去看看ViewGroup的dispatchTouchEvent函数:

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) { 
        .........
        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) {
                cancelAndClearTouchTargets(ev);
                resetTouchState();
            }
    
            // 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;
            }
            ............
            // 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 (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 = buildOrderedChildList();
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
                        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);
                            .......
    
                            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;
                            }
                        }
                        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;
    }


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  • 原文地址:https://www.cnblogs.com/163yun/p/9705698.html
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