android事件分发（二）

红太狼 2022-03-28 13:57 195阅读 0赞

非常早之前写过一篇android[事件分发][Link 1]的博客，主要写的是它是怎样分发的，具体非常多原理的东西都没有涉及到。今天就从源代码看android怎样控制它的分发机制。  
鉴于手机屏幕的限制，所以android选择了分层的方式布局，这就引出了今天的主题－－事件分发  
当你点击一个控件或者某个空白区域时,怎样确定你点击的位置,事件又是怎样传递到这里的,相信看过上篇博客的都知道怎样传递了,以下就開始看源代码

public boolean dispatchTouchEvent(MotionEvent event) {
            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;
        }

从上面的代码能够看出主要代码就是第三个if了,首先检測事件的安全性,推断监听事件是否为空,是否有touch事件,推断当前控件是否为enable,回调onTouch()事件的返回值,那个down和up时停止滚动等先无论,看核心代码.

ListenerInfo getListenerInfo() {
            if (mListenerInfo != null) {
                return mListenerInfo;
            }
            mListenerInfo = new ListenerInfo();
            return mListenerInfo;
        }

从以上这段代码会看出mListenerInfo一定会被赋值,当然限定于ListenerInfo有的监听事件,监听事件不为空时,监听事件就存在onTouchListener,第三个条件基本都满足,Android控件默认的情况下都是enable,除非你手动设置,第四个条件,假设回调的onTouch()事件返回的为true,dispatchTouchEvent(event)直接返回true,否则继续走onTouchEvent(event)  
从上面能够看出onTouchEvent(event)就是dispatchTouchEvent(event)的小棋子,小棋子被运行的话,返回值就是dispatchTouchEvent(event)的返回值,也就验证了之前说的假设dispatchTouchEvent(event)返回true就交给onTouchEvent(event)去运行

public boolean onTouchEvent(MotionEvent event) {
            final float x = event.getX();
            final float y = event.getY();
            final int viewFlags = mViewFlags;
    
            if ((viewFlags & ENABLED_MASK) == DISABLED) {
                if (event.getAction() == 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));
            }
    
            if (mTouchDelegate != null) {
                if (mTouchDelegate.onTouchEvent(event)) {
                    return true;
                }
            }
    
            if (((viewFlags & CLICKABLE) == CLICKABLE ||
                    (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
                switch (event.getAction()) {
                    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) {
                                // 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();
                        }
                        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();
                        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;
        }

好长的代码,还是看核心代码,前面介绍了Android的控件默认都是enable的,所以第一个if跳过,直接看第三个if,控件是否可点击(或者是是否有长按事件)进入switch中,以下就開始Down,Move,Up  
先来看ACTION\_DOWN,首先推断当前点击down事件的操作,假设点击到menu时,显示菜单,返回true,程序直接跳出

protected boolean performButtonActionOnTouchDown(MotionEvent event) {
            if ((event.getButtonState() & MotionEvent.BUTTON_SECONDARY) != 0) {
                if (showContextMenu(event.getX(), event.getY(), event.getMetaState())) {
                    return true;
                }
            }
            return false;
        }

再来看一下ACTION\_UP,按不按的那一堆直接跳过,直接看核心代码 performClick(),这个是干嘛的,进去看看

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;
            }
    
            sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
            return result;
        }

这里看到了熟悉的代码onClick(),仅仅要li和li.mOnClickListener不为空,onClick()就会被运行,上面说过li不会为空,li.mOnClickListener赋值例如以下:

public void setOnClickListener(OnClickListener l) {
            if (!isClickable()) {
                setClickable(true);
            }
            getListenerInfo().mOnClickListener = l;
        }

仅仅要注冊了点击事件li.mOnClickListener也不会为空,所以仅仅要你注冊点击事件onClick()就会被运行,当然前提是运行Up事件哦!  
看完这段代码是不是认为掉坑里了,Down,Move,Up,Cancel事件怎样运行都会返回true,除非这个控件不能点击,为什么会返回true呢,为了能够之后后面的action,假设程序运行完Down返回false的话后面的Move.Up都不会运行  
总结一下view的事件分发结果,首先当你touch到某个点或者区域的时候,先去找这个控件的dispatchTouchEvent(event),该控件没有的话继续找父类,直到找到为止,然后開始事件分发,假设该控件重写了onTouch()事件,返回true的话,dispatchTouchEvent(event)直接返回true,返回false的话,继续运行onTouchEvent(event),假设该控件没有点击事件,像ImageView,TextView等直接返回false,假设存在点击事件,像Button,ImageButton等去运行Down,Move,Up等,返回true,dispatchTouchEvent(event)相应的返回true or false

以上就是Android中view的事件分发的内容了,以下我们继续研究viewgroup的事件分发,viewgroup继承自view,所以在事件分发上也有一定的类似性,仅仅是viewgroup更复杂一些

先来看viewgroup的dispatchTouchEvent(event)

@Override
        public boolean dispatchTouchEvent(MotionEvent ev) {
            if (mInputEventConsistencyVerifier != null) {
                mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
            }
    
            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
                    // due to an app switch, ANR, or some other state change.
                    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;
                }
    
                // 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) {
                    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)) { 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; }`

喔,好长啊,还是同上,仅仅看核心代码,首先推断当前是不是down状态或者是首次touch,然后推断disallowIntercept的值,默认情况下为false,你也能够通过调用以下这种方法改变它的值

public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
    
            if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
                // We're already in this state, assume our ancestors are too
                return;
            }
    
            if (disallowIntercept) {
                mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
            } else {
                mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
            }
    
            // Pass it up to our parent
            if (mParent != null) {
                mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
            }
        }

继续上面说的,怎么突然间出现了onInterceptTouchEvent(),这种方法就是传说中的事件拦截了

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

原来这个高大上的拦截事件就两行,直接给你return false,也就说默认情况下是不拦截的,当然There are no touch targets and this action is not an initial down的情况下也是拦截的.假设当前事件被拦截,事件就不再向下分发,假设当前事件没有被拦截而且没有取消，继续走view的事件分发

最后总结一下：点击到某个点，先传递到viewgroup的  
dispatchTouchEvent(event)，然后传递到onInterceptTouchEvent(event)，推断当前是否拦截，不拦截就继续走view的拦截方式。拦截就谁拦截谁处理。

分析的不够仔细，具体内容请看源代码。自行补脑。

[Link 1]: http://blog.csdn.net/elinavampire/article/details/42915507