Android触屏事件处理流程浅析

在android触屏事件中，我们经常会碰到onclick(),onTouch(),onTouchEven()等方法，那谁会先执行，执行顺序又是怎么样呢？

View的触屏事件处理

为弄清除上面那些，首先从源码入手，看看其整个触屏事件分发的过程．
先从dispatchTouchEvent()分析:

/**
     * Pass the touch screen motion event down to the target view, or this
     * view if it is the target.
     *
     * @param event The motion event to be dispatched.
     * @return True if the event was handled by the view, false otherwise.
     */
    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)) {
            //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;
            }
        }       
        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;
    }

分析这段源码，便知道有些细节地方，如果目标View不能获取焦点，那么就不会处理触屏事件，而是直接返回false ，否则判断目标View是否满足注册了onTouchListener()监听以及可点击的条件，满足则会调用onTouch()，如果onTouch()返回true,那么就不会再执行onTouchEvent()了，如果前面onTouch()返回了false,那么就会由onTouchEvent()的返回值来确定最终的结果值了,因此遵从onTouch()==true? true:onTouchEvent()规则．在这段源码中，可以看出其执行顺序的优先级是dispatchOnTouchEvent()>>>>onTouch()>>>>onTouchEvent()．
再来看看onTouchEvent()在View.java源码中有的实现:

/**
     * Implement this method to handle touch screen motion events.
     * 

     * If this method is used to detect click actions, it is recommended that
     * the actions be performed by implementing and calling
     * {@link #performClick()}. This will ensure consistent system behavior,
     * including:
     * 

     * 
obeying click sound preferences
     * 
dispatching OnClickListener calls
     * 
handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
     * accessibility features are enabled
     * 
     *
     * @param event The motion event.
     * @return True if the event was handled, false otherwise.
     */
    public boolean onTouchEvent(MotionEvent event) {
        final float x = event.getX();
        final float y = event.getY();
        final int viewFlags = mViewFlags;
        final int action = event.getAction();

        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);
        }

        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }

        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);
                       }
                        //如果onLongClick()返回true,就不会执行onClick()
                        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();
                                }
                            }
                        }

                        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:
                    mHasPerformedLongPress = false;

                    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);
                    }
                    break;

                case MotionEvent.ACTION_CANCEL:
                    setPressed(false);
                    removeTapCallback();
                    removeLongPressCallback();
                    mInContextButtonPress = false;
                    mHasPerformedLongPress = false;
                    mIgnoreNextUpEvent = false;
                    break;

                case MotionEvent.ACTION_MOVE:
                    drawableHotspotChanged(x, y);

                    // Be lenient about moving outside of buttons
                    if (!pointInView(x, y, mTouchSlop)) {
                        // Outside button
                        removeTapCallback();
                        if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                            // Remove any future long press/tap checks
                            removeLongPressCallback();

                            setPressed(false);
                        }
                    }
                    break;
            }

            return true;
        }

        return false;
    }

 private void checkForLongClick(int delayOffset) {
        if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
            mHasPerformedLongPress = false;

            if (mPendingCheckForLongPress == null) {
                mPendingCheckForLongPress = new CheckForLongPress();
            }
            mPendingCheckForLongPress.rememberWindowAttachCount();
            postDelayed(mPendingCheckForLongPress,
                    ViewConfiguration.getLongPressTimeout() - delayOffset);
        }
    }

private final class CheckForTap implements Runnable {
        public float x;
        public float y;

        @Override
        public void run() {
            mPrivateFlags &= ~PFLAG_PREPRESSED;
            setPressed(true, x, y);
            checkForLongClick(ViewConfiguration.getTapTimeout());
        }
    }

private final class CheckForLongPress implements Runnable {
        private int mOriginalWindowAttachCount;

        @Override
        public void run() {
            if (isPressed() && (mParent != null)
                    && mOriginalWindowAttachCount == mWindowAttachCount) {
                    //返回true的话,就不执行onclick()
                if (performLongClick()) {
                    mHasPerformedLongPress = true;
                }
            }
        }

        public void rememberWindowAttachCount() {
            mOriginalWindowAttachCount = mWindowAttachCount;
        }
    }

 private final class PerformClick implements Runnable {
        @Override
        public void run() {
            performClick();
        }
    }

这段代码稍微多一点，但也有好多细节要注意的，如果有目标View有传入过TouchDelegate对象，那么一切来到这里的触屏事件都会交给其TouchDelegate.onTouchEvent()处理并返回true,在ACTION_DOWN阶段中，如果顶层容器不是滚动类的容器，那么直接通知目标View转变按压视图状态，并且开始通过postDelayed()来设置CheckForLongPress()对象，一旦长按时间超过了ViewConfiguration.getLongPressTimeout()，CheckForLongPress()对象就会执行对应长按回调方法，如果顶层容器是滚动类的容器，那么会通过postDelayed()传入CheckForTap()对象,直到ViewConfiguration.getTapTimeout()时候才让View转变按压视图状态，而不是立刻改变，同时CheckForTap()对象也创建对应CheckForLongPress()对象．同时还带有prepressed时期标记，在ACTION_UP阶段中,如果目标View没有长按(既不会执行CheckForLongPress()对象里的方法)，同时不能获取到焦点并返回false，那么便会执行PerformClick()对应方法，从而调用OnClickListener.onclick(),还有最后一点的细节就是，如果目标View满足CLICKABLE,LONG_CLICKABLE,CONTEXT_CLICKABLE其中一个条件，那么onTouchEvent()就会返回true.在经过一些列的分析，可以看出其执行的顺序优先级：`onTouchEvent()>>>>TouchDelegate.onTouchEvent()>>>>onLongClick()>>>>onClick().

ViewGroup的触屏分发实现

上面的那段是基于View.java源码分析,那么来分析一下其ViewGroup.java源码,看看其又是如何分发触屏事件的.

/**
     * 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.
     */
     //用来派发给子View触屏事件
    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);
            //如果child为空,则会回调父类的dispatchTouchEvent()
            if (child == null) {
                handled = super.dispatchTouchEvent(event);
            } else {
                handled = child.dispatchTouchEvent(event);
            }
            event.setAction(oldAction);
            return handled;
        }

        // Calculate the number of pointers to deliver.
        final int oldPointerIdBits = event.getPointerIdBits();
        final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;

        // If for some reason we ended up in an inconsistent state where it looks like we
        // might produce a motion event with no pointers in it, then drop the event.
        if (newPointerIdBits == 0) {
            return false;
        }

        // If the number of pointers is the same and we don't need to perform any fancy
        // irreversible transformations, then we can reuse the motion event for this
        // dispatch as long as we are careful to revert any changes we make.
        // Otherwise we need to make a copy.
        final MotionEvent transformedEvent;
        if (newPointerIdBits == oldPointerIdBits) {
            if (child == null || child.hasIdentityMatrix()) {
                if (child == null) {
                    handled = super.dispatchTouchEvent(event);
                } else {
                   //如果触屏事件设置偏移量以和支持单位矩阵变换的子view一致
                   //如子View做一些平移等动画操作时的点击
                    final float offsetX = mScrollX - child.mLeft;
                    final float offsetY = mScrollY - child.mTop;
                    event.offsetLocation(offsetX, offsetY);

                    handled = child.dispatchTouchEvent(event);

                    event.offsetLocation(-offsetX, -offsetY);
                }
                return handled;
            }
            transformedEvent = MotionEvent.obtain(event);
        } else {
            transformedEvent = event.split(newPointerIdBits);
        }

        // Perform any necessary transformations and dispatch.
        if (child == null) {
            handled = super.dispatchTouchEvent(transformedEvent);
        } else {
            final float offsetX = mScrollX - child.mLeft;
            final float offsetY = mScrollY - child.mTop;
            transformedEvent.offsetLocation(offsetX, offsetY);
            if (! child.hasIdentityMatrix()) {
                //恢复原来触屏事件发生坐标,即相当于撤销了offsetLocation()作用
                transformedEvent.transform(child.getInverseMatrix());
            }

            handled = child.dispatchTouchEvent(transformedEvent);
        }

        // Done.
        transformedEvent.recycle();
        return handled;
    }

在触屏事件分发给子View的逻辑中可以知道一个细节,如果child为空,那么会回调父类的dispatchTouchEvent()方法,否则就调用子View的dispatchTouchEvent(),执行顺序的优先级:当前ViewGroup的dispatchTouchEvent()>>>>>childView!=null?dispatchTouchEvent():super.dispatchTouchEvent().

 /* Describes a touched view and the ids of the pointers that it has captured.
     *
     * This code assumes that pointer ids are always in the range 0..31 such that
     * it can use a bitfield to track which pointer ids are present.
     * As it happens, the lower layers of the input dispatch pipeline also use the
     * same trick so the assumption should be safe here...
     */
    private static final class TouchTarget {
        private static final int MAX_RECYCLED = 32;
        private static final Object sRecycleLock = new Object[0];
        private static TouchTarget sRecycleBin;
        private static int sRecycledCount;

        public static final int ALL_POINTER_IDS = -1; // all ones

        // The touched child view.
        public View child;

        // The combined bit mask of pointer ids for all pointers captured by the target.
        public int pointerIdBits;//通过位标记来记录节点在链表的位置

        // The next target in the target list.
        public TouchTarget next;

        private TouchTarget() {
        }

        public static TouchTarget obtain(View child, int pointerIdBits) {
            final TouchTarget target;
            synchronized (sRecycleLock) {
                if (sRecycleBin == null) {
                    target = new TouchTarget();
                } else {
                    target = sRecycleBin;
                    sRecycleBin = target.next;
                     sRecycledCount--;
                    target.next = null;
                }
            }
            target.child = child;
            target.pointerIdBits = pointerIdBits;
            return target;
        }

        public void recycle() {
            synchronized (sRecycleLock) {
                if (sRecycledCount < MAX_RECYCLED) {
                    next = sRecycleBin;
                    sRecycleBin = this;
                    sRecycledCount += 1;
                } else {
                    next = null;
                }
                child = null;
            }
        }
    }

通过链表方式来维护触屏事件的,但在这里有个很巧妙的地方,也通过sRecycleBin指针来复用对象,很多地方都用类似的技巧来复用对象,如listView创建item对象,具体过程如图所示(假设初始化时,不串联对象):

在dispatchTouchEvent()方法中,由于这段代码还比较长,很多细节,因此我把代码分成两个阶段去分析.

//第一阶段 拦截事件时,触屏事件的分发处理
//即某段时刻intercepted会返回true.
 /**
     * {@inheritDoc}
     */
    @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) {
                // 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
                // 在ACTION_DOWN会丢弃以前的触屏事件和清除触屏状态
                cancelAndClearTouchTargets(ev);
                resetTouchState();
            }

            // Check for interception.
            final boolean intercepted;
            //在ACTION_DOWN时候会执行或有目标子View的时候
            //如果没有找到处理触屏事件的View那么其他的
            //后续触屏事件会被当前的容器拦截,不再分发给子View
            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;
            }

            // 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){
              //省略另一阶段的代码.............................   
             }                    
            // Dispatch to touch targets.
            //拦截事件且没有子View处理触屏事件的时候,即回调父类的dispatchTransformedTouchEvent()
            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.
                //会把在拦截事件前所捕获到的触屏事件交给子View去处理,拦截事件后的触屏事件交给自己去
                处理
                TouchTarget predecessor = null;//前个触屏事件节点
                TouchTarget target = mFirstTouchTarget;//当前触屏事件节点
                while (target != null) {
                    final TouchTarget next = target.next;
                    if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                        handled = true;
                    } else {
                        //派发拦截事件前的触屏事件给子View,如果拦截(intercepted==true)
                        //则触屏事件交给父类dispatchOnTouchEvent()
                        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) {
                //清除触屏事件状态
                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;
    }

在分析上面第一阶段时,注意到一些细节处理,如果ViewGroup没有嵌套子View的话,那么就会回调父类的dispatchTouchEvent(),但如果ViewGroup有嵌套子View,但没有一开始拦截的话,那就会将拦截前的触屏事件交给子ViewdispatchTouchEvent()去处理,拦截后的触屏事件交给父类的dispatchTouchEvent()去处理.还有一点就是如果某个子View在dispatchTouchEvent()和onTouch()和onTouchEvent()都不处理触屏事件ACTION_DOWN或ACTON_MOVE等阶段,即都返回false,那子View就再也接受不到触屏事件的后续阶段了(如ACTION_UP).

//第二阶段不拦截触屏事件
 /**
     * {@inheritDoc}
     */
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
            //省略代码............................................
            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 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 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;
                    }
                }
            }
        //省略代码.........................................................
        return handled;
    }

这段代码主要处理ACTION_DOWN阶段,只在ACTION_DOWN阶段仅一次或0次调用onInterceptTouchEvent()来决定要不要拦截触屏事件,如果不拦截,那就找消费触屏事件的子View,即子View处理触屏事件的最终结果返回true,然后做一些记录操,最后用链表串联触屏对象.在结合第一段阶段的代码,可以看出其触屏事件执行顺序的优先级:当前容器的dispatchTouchEvent()>>>>>onInterceptTouchEvent()>>>>>childView!=null?dispatchTouchEvent():super.dispatchTouchEvent().

触屏事件处理DEMO

上面围绕一大堆源码分析后,可能很容易被搞混,为印象更加深刻,基于上面理论实践一个demo来验证,并画出对应的处理流程图.

public class MyButton extends Button implements View.OnClickListener,View.OnTouchListener,View.OnLongClickListener{

    private static final String TAG = MyButton.class.getName();

    public MyButton(Context context, AttributeSet attrs) {
        super(context, attrs);
        setOnClickListener(this);
        setOnTouchListener(this);
        setOnLongClickListener(this);
        Button button=new Button(context){
            @Override
            public boolean onTouchEvent(MotionEvent event) {
                Log.i(TAG,"OtherButton>>>>>>>>>>>onTouchEvent()");
                return true;
            }
        };
        DisplayMetrics displayMetrics=context.getResources().getDisplayMetrics();
        setTouchDelegate(new TouchDelegate(new Rect(0,0,displayMetrics.widthPixels,displayMetrics.heightPixels),button));
    }

    @Override
    public boolean onLongClick(View view) {
        Log.i(TAG,"MyButton>>>>>>>>>>>onLongClick");
        return false;
    }


    @Override
    public boolean onTouch(View view, MotionEvent motionEvent) {
        Log.i(TAG,"MyButton>>>>>>>>>>>onTouch");
        return false;
    }

    @Override
    public void onClick(View view) {
        Log.i(TAG,"MyButton>>>>>>>>>>>onClick");

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.i(TAG,"MyButton>>>>>>>>>>>onTouchEvent");
        return super.onTouchEvent(event);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        Log.i(TAG,"event_action>>>>>>>>>>>"+event.getAction());
        Log.i(TAG,"MyButton>>>>>>>>>>>DispatchTouchEvent");
        return super.dispatchTouchEvent(event);
    }
}

将代理的button的onTouch()返回false.其短按和长按事件处理流程如图:
短按:

长按:

对于View处理触屏事件的其他的情况,我就不再一一测试了,总的来说,View处理触屏事件流程就如图所示:

//子布局
public class MyButton extends Button implements View.OnClickListener, View.OnTouchListener, View.OnLongClickListener {

  private static final String TAG = MyButton.class.getName();

  public MyButton(Context context, AttributeSet attrs) {
    super(context, attrs);    
  }
  @Override
  public boolean dispatchTouchEvent(MotionEvent event) {
    switch (event.getAction()){
      case MotionEvent.ACTION_DOWN:
        Log.i(TAG, "ACTION_DOWN>>>>>>>>>>>DispatchTouchEvent");
        break;
      case MotionEvent.ACTION_MOVE:
        Log.i(TAG, "ACTION_MOVE>>>>>>>>>>>DispatchTouchEvent");
        break;
      case MotionEvent.ACTION_UP:
        Log.i(TAG, "ACTION_UP>>>>>>>>>>>DispatchTouchEvent");
        break;
    }
    return false;
  }

}

//父布局,该布局会嵌套MyButton
public class MyRelativeLayout extends RelativeLayout {

  private static final String TAG = MyRelativeLayout.class.getName();

  public MyRelativeLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    //setClickable(true);
  }

  @Override
  public boolean dispatchTouchEvent(MotionEvent event) {
    switch (event.getAction()){
      case MotionEvent.ACTION_DOWN:
        Log.i(TAG, "ACTION_DOWN>>>>>>>>>>>dispatchTouchEvent");
        break;
      case MotionEvent.ACTION_MOVE:
        Log.i(TAG, "ACTION_MOVE>>>>>>>>>>>dispatchTouchEvent");
        break;
      case MotionEvent.ACTION_UP:
        Log.i(TAG, "ACTION_UP>>>>>>>>>>>dispatchTouchEvent");
        break;
    }
    return super.dispatchTouchEvent(event);
  }

  @Override
  public boolean onInterceptTouchEvent(MotionEvent ev) {
    switch (ev.getAction()){
      case MotionEvent.ACTION_DOWN:
        Log.i(TAG, "ACTION_DOWN>>>>>>>>>>>onInterceptTouchEvent");
        break;
      case MotionEvent.ACTION_MOVE:
        Log.i(TAG, "ACTION_MOVE>>>>>>>>>>>onInterceptTouchEvent");
        break;
      case MotionEvent.ACTION_UP:
        Log.i(TAG, "ACTION_UP>>>>>>>>>>>onInterceptTouchEvent");
        break;
    }
    return false;
  }

  @Override
  public String toString() {
    return "MyRelativeLayout";
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()){
      case MotionEvent.ACTION_DOWN:
        Log.i(TAG, "ACTION_DOWN>>>>>>>>>>>onTouchEvent");
        break;
      case MotionEvent.ACTION_MOVE:
        Log.i(TAG, "ACTION_MOVE>>>>>>>>>>>onTouchEvent");
        break;
      case MotionEvent.ACTION_UP:
        Log.i(TAG, "ACTION_UP>>>>>>>>>>>onTouchEvent");
        break;
    }
    return true;
  }
}

日志可以看出子View没有消费触屏事件的话,会回传给父容器去处理触屏事件的,并且只在ACTION_DOWN阶段调用onInterceptTouchEvent(),再把MyRelativeLayout.onInterceptTouchEvent()改为true.

再把MyRelativeLayout.onTouchEvent()返回false,那么又会怎么样呢?

public class MainActivity extends AppCompatActivity {

  private static final String TAG = MainActivity.class.getName();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
  }

  @Override
  public boolean dispatchTouchEvent(MotionEvent ev) {
    switch (ev.getAction()){
      case MotionEvent.ACTION_DOWN:
        Log.i(TAG, "ACTION_DOWN>>>>>>>>>>>dispatchTouchEvent");
        break;
      case MotionEvent.ACTION_MOVE:
        Log.i(TAG, "ACTION_MOVE>>>>>>>>>>>dispatchTouchEvent");
        break;
      case MotionEvent.ACTION_UP:
        Log.i(TAG, "ACTION_UP>>>>>>>>>>>dispatchTouchEvent");
        break;
    }
    return super.dispatchTouchEvent(ev);
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()){
      case MotionEvent.ACTION_DOWN:
        Log.i(TAG, "ACTION_DOWN>>>>>>>>>>>onTouchEvent");
        break;
      case MotionEvent.ACTION_MOVE:
        Log.i(TAG, "ACTION_MOVE>>>>>>>>>>>onTouchEvent");
        break;
      case MotionEvent.ACTION_UP:
        Log.i(TAG, "ACTION_UP>>>>>>>>>>>onTouchEvent");
        break;
    }
    return true;
  }
}

子View再也没有收到触屏事件了吧,如果最顶层容器onTouchEvent()返回false不消费触屏事件的话,那么回回传给Actvitiy的onTouchEvent()去处理,即使Activitiy的onTouchEvent()返回false,也会能接受到触屏事件的后续阶段.到这里,我画个总的流程图来概况一下: