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MyButtonpublic 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:

View的触屏事件处理

ViewGroup的触屏分发实现

触屏事件处理DEMO

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