Android KeyEvent分发机制

简介

KeyEvent的分发机制和TouchEvent的分发机制略有不同，KeyEvent向下分发的事件没有被消费，并且KeyCode为KEYCODE_DPAD_LEFT,KEYCODE_DPAD_RIGHT,KEYCODE_DPAD_UP,KEYCODE_DPAD_DOWN,那么会按方向查找下一个控件并获取焦点。

触摸事件分发机制传送门： Android触摸事件分发机制源码分析

分发机制分析

先放上整体流程图，稍后再详细解释：

ViewRootImpl是所有View的顶层容器，所以从ViewRootImpl着手。ViewRootImpl的dispatchInputEvent()方法，向消息队列发出MSG_DISPATCH_INPUT_EVENT消息，Handler处理消息并调用ViewRootImpl的enqueueInputEvent()方法，将QueuedInputEvent插入到未处理KeyEvent队列的尾部。

enqueueInputEvent()方法具体实现：

void enqueueInputEvent(InputEvent event,InputEventReceiver receiver, int flags, boolean processImmediately) {    adjustInputEventForCompatibility(event);    QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);    QueuedInputEvent last = mPendingInputEventTail;    if (last == null) {        mPendingInputEventHead = q;        mPendingInputEventTail = q;    } else {        last.mNext = q;        mPendingInputEventTail = q;    }    mPendingInputEventCount += 1;    Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,mPendingInputEventCount);    if (processImmediately) {        doProcessInputEvents();    } else {        scheduleProcessInputEvents();    }}

keyEvent插入未处理事件队列后，接下来要处理这些事件了。有两种处理方式，直接处理和向Handler发送异步消息处理。这里只分析直接处理的情况。

doProcessInputEvents()方法遍历未处理事件队列逐个处理：

void doProcessInputEvents() {        // Deliver all pending input events in the queue.        while (mPendingInputEventHead != null) {            QueuedInputEvent q = mPendingInputEventHead;            mPendingInputEventHead = q.mNext;            if (mPendingInputEventHead == null) {                mPendingInputEventTail = null;            }            q.mNext = null;            mPendingInputEventCount -= 1;            Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,                    mPendingInputEventCount);            long eventTime = q.mEvent.getEventTimeNano();            long oldestEventTime = eventTime;            if (q.mEvent instanceof MotionEvent) {                MotionEvent me = (MotionEvent)q.mEvent;                if (me.getHistorySize() > 0) {                    oldestEventTime = me.getHistoricalEventTimeNano(0);                }            }            mChoreographer.mFrameInfo.updateInputEventTime(eventTime, oldestEventTime);            deliverInputEvent(q);        }        // We are done processing all input events that we can process right now        // so we can clear the pending flag immediately.        if (mProcessInputEventsScheduled) {            mProcessInputEventsScheduled = false;            mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);        }    }

QueuedInputEvent交给deliverInputEvent()方法来处理：

private void deliverInputEvent(QueuedInputEvent q) {    Trace.asyncTraceBegin(Trace.TRACE_TAG_VIEW,"deliverInputEvent",        q.mEvent.getSequenceNumber());    if (mInputEventConsistencyVerifier != null) {        mInputEventConsistencyVerifier.onInputEvent(q.mEvent, 0);    }    InputStage stage;    if (q.shouldSendToSynthesizer()) {        stage = mSyntheticInputStage;    } else {        stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;    }    if (stage != null) {        stage.deliver(q);    } else {        finishInputEvent(q);    }}

重头戏来了，这里出现了个InputStage对象stage，它是什么，从哪来？在ViewRootImpl的setView()方法中初始化InputStage对象：

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {    // Set up the input pipeline.    CharSequence counterSuffix = attrs.getTitle();    mSyntheticInputStage = new SyntheticInputStage();    InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);    InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,"aq:native-post-ime:" + counterSuffix);    InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);    InputStage imeStage = new ImeInputStage(earlyPostImeStage,        "aq:ime:" + counterSuffix);    InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);    InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,        "aq:native-pre-ime:" + counterSuffix);    mFirstInputStage = nativePreImeStage;    mFirstPostImeInputStage = earlyPostImeStage;}

InPuStage实际上是个管道，也就是责任链模式，事件在前一个InputStage未处理完会继续向下传递。KeyEvent的处理单元是ViewPostImeInputStage。

InputStage的deliver()方法会调用onProcess()方法，这个是InputStage子类具体处理KeyEvent的方法。看看ViewPostImeInputStage的onProcess()方法实现：

protected int onProcess(QueuedInputEvent q) {    if (q.mEvent instanceof KeyEvent) {        return processKeyEvent(q);    } else {        final int source = q.mEvent.getSource();        if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {            return processPointerEvent(q);        } else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {            return processTrackballEvent(q);        } else {            return processGenericMotionEvent(q);        }    }}

可以看到里面调用了processKeyEvent()方法：

private int processKeyEvent(QueuedInputEvent q) {    final KeyEvent event = (KeyEvent)q.mEvent;    // Deliver the key to the view hierarchy.    if (mView.dispatchKeyEvent(event)) {        return FINISH_HANDLED;    }    if (shouldDropInputEvent(q)) {        return FINISH_NOT_HANDLED;    }    // If the Control modifier is held, try to interpret the key as a shortcut.    if (event.getAction() == KeyEvent.ACTION_DOWN        && event.isCtrlPressed()        && event.getRepeatCount() == 0        && !KeyEvent.isModifierKey(event.getKeyCode())) {        if (mView.dispatchKeyShortcutEvent(event)) {            return FINISH_HANDLED;        }        if (shouldDropInputEvent(q)) {            return FINISH_NOT_HANDLED;            }        }        // Apply the fallback event policy.        if (mFallbackEventHandler.dispatchKeyEvent(event)) {            return FINISH_HANDLED;        }        if (shouldDropInputEvent(q)) {            return FINISH_NOT_HANDLED;        }        // Handle automatic focus changes.        if (event.getAction() == KeyEvent.ACTION_DOWN) {            int direction = 0;            switch (event.getKeyCode()) {                case KeyEvent.KEYCODE_DPAD_LEFT:                    if (event.hasNoModifiers()) {                        direction = View.FOCUS_LEFT;                    }                    break;                case KeyEvent.KEYCODE_DPAD_RIGHT:                    if (event.hasNoModifiers()) {                        direction = View.FOCUS_RIGHT;                    }                    break;                case KeyEvent.KEYCODE_DPAD_UP:                    if (event.hasNoModifiers()) {                        direction = View.FOCUS_UP;                    }                    break;                case KeyEvent.KEYCODE_DPAD_DOWN:                    if (event.hasNoModifiers()) {                        direction = View.FOCUS_DOWN;                    }                    break;                case KeyEvent.KEYCODE_TAB:                    if (event.hasNoModifiers()) {                        direction = View.FOCUS_FORWARD;                    } else if (event.hasModifiers(KeyEvent.META_SHIFT_ON)) {                        direction = View.FOCUS_BACKWARD;                    }                    break;            }            if (direction != 0) {                View focused = mView.findFocus();                if (focused != null) {                    View v = focused.focusSearch(direction);                        if (v != null && v != focused) {                        // do the math the get the interesting rect                        // of previous focused into the coord system of                        // newly focused view                        focused.getFocusedRect(mTempRect);                        if (mView instanceof ViewGroup) {                            ((ViewGroup) mView).offsetDescendantRectToMyCoords(focused, mTempRect);                                ((ViewGroup) mView).offsetRectIntoDescendantCoords(v, mTempRect);                        }                        if (v.requestFocus(direction,mTempRect)) {                            playSoundEffect(SoundEffectConstants                                        .getContantForFocusDirection(direction));                            return FINISH_HANDLED;                        }                    }                    // Give the focused view a last chance to handle the dpad key.                    if (mView.dispatchUnhandledMove(focused, direction)) {                        return FINISH_HANDLED;                    }                } else {                    // find the best view to give focus to in this non-touch-mode with no-focus                    View v = focusSearch(null, direction);                    if (v != null && v.requestFocus(direction)) {                        return FINISH_HANDLED;                    }                }            }        }    return FORWARD;}

看到调用了DecorView的dispatchKeyEvent()方法开始向View传递KeyEvent事件，如果事件未被消费，并且KeyCode为KEYCODE_DPAD_LEFT,KEYCODE_DPAD_RIGHT,KEYCODE_DPAD_UP,KEYCODE_DPAD_DOWN,那么会按方向查找下一个控件并获取焦点。这部分内容下一节节介绍。

focusSearch流程分析

processKeyEvent()在调用DecorView的dispatchKeyEvent()返回false后，先确定方向，并且根据当前是否有已获取焦点控件用不同的方式进行查找。

focusSearch()方法的大致流程：
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-67AmDGeV-1586764136973)(https://www.github.com/wslaimin/blog/raw/master/pics/focusSearch.png)]

当前focused!=null的情况

当前focused!=null时，调用View的focusSearch()方法，寻找下一个获取焦点控件，代码如下：

public View focusSearch(@FocusRealDirection int direction) {    if (mParent != null) {        return mParent.focusSearch(this, direction);    } else {        return null;    }}

实际上是调用了ViewGroup的focusSearch()方法：

public View focusSearch(View focused, int direction) {    if (isRootNamespace()) {        // root namespace means we should consider ourselves the top of the        // tree for focus searching; otherwise we could be focus searching        // into other tabs.  see LocalActivityManager and TabHost for more info        return FocusFinder.getInstance().findNextFocus(this, focused, direction);    } else if (mParent != null) {        return mParent.focusSearch(focused, direction);    }        return null;}

可以看到这个寻找过程是不断的调用上层容器的focusSearch()方法，直到DecorView才真正调用FocusFinder的findNextFocus()方法寻找下一个获取焦点控件。findNextFocus()方法后面再分析。

当focused==null的情况

当前focused==null时，ViewRootImpl调用focusSearch()方法，focusSearch()方法中调用了FocusFinder的findNextFocus()方法。接下来中点介绍findNextFocus()方法。

findNextFocus()方法实现：

public final View findNextFocus(ViewGroup root, View focused, int direction) {    return findNextFocus(root, focused, null, direction);}

调用了重载方法findNextFocus():

 private View findNextFocus(ViewGroup root, View focused, Rect focusedRect, int direction) {    View next = null;    if (focused != null) {        next = findNextUserSpecifiedFocus(root, focused, direction);    }    if (next != null) {        return next;    }    ArrayList<View> focusables = mTempList;    try {        focusables.clear();        root.addFocusables(focusables, direction);        if (!focusables.isEmpty()) {            next = findNextFocus(root, focused, focusedRect, direction, focusables);    }    } finally {        focusables.clear();    }    return next;}

addFocusables()方法返回root下所有能获取焦点的控件，然后继续调用重载方法findNextFocus():

private View findNextFocus(ViewGroup root, View focused, Rect focusedRect,int direction, ArrayList<View> focusables) {    if (focused != null) {        if (focusedRect == null) {            focusedRect = mFocusedRect;        }        // fill in interesting rect from focused        focused.getFocusedRect(focusedRect);        root.offsetDescendantRectToMyCoords(focused, focusedRect);    } else {        if (focusedRect == null) {            focusedRect = mFocusedRect;            // make up a rect at top left or bottom right of root            switch (direction) {                case View.FOCUS_RIGHT:                case View.FOCUS_DOWN:                    setFocusTopLeft(root, focusedRect);                break;                case View.FOCUS_FORWARD:                    if (root.isLayoutRtl()) {                        setFocusBottomRight(root, focusedRect);                    } else {                        setFocusTopLeft(root, focusedRect);                    }                break;                case View.FOCUS_LEFT:                case View.FOCUS_UP:                    setFocusBottomRight(root, focusedRect);                break;                case View.FOCUS_BACKWARD:                    if (root.isLayoutRtl()) {                        setFocusTopLeft(root, focusedRect);                    } else {                        setFocusBottomRight(root, focusedRect);                    break;                    }            }        }    }    switch (direction) {        case View.FOCUS_FORWARD:        case View.FOCUS_BACKWARD:            return findNextFocusInRelativeDirection(focusables, root, focused, focusedRect,direction);        case View.FOCUS_UP:        case View.FOCUS_DOWN:        case View.FOCUS_LEFT:        case View.FOCUS_RIGHT:            return findNextFocusInAbsoluteDirection(focusables, root, focused,focusedRect, direction);        default:            throw new IllegalArgumentException("Unknown direction: " + direction);    }}

由于focusedRect==null，先根据焦点移动方向确定focusedRect，然后调用findNextFocusInAbsoluteDirection()方法:

View findNextFocusInAbsoluteDirection(ArrayList<View> focusables, ViewGroup root, View focused,Rect focusedRect, int direction) {    // initialize the best candidate to something impossible    // (so the first plausible view will become the best choice)    mBestCandidateRect.set(focusedRect);    switch(direction) {        case View.FOCUS_LEFT:            mBestCandidateRect.offset(focusedRect.width() + 1, 0);        break;        case View.FOCUS_RIGHT:            mBestCandidateRect.offset(-(focusedRect.width() + 1), 0);        break;        case View.FOCUS_UP:            mBestCandidateRect.offset(0, focusedRect.height() + 1);        break;        case View.FOCUS_DOWN:            mBestCandidateRect.offset(0, -(focusedRect.height() + 1));    }    View closest = null;    int numFocusables = focusables.size();    for (int i = 0; i < numFocusables; i++) {        View focusable = focusables.get(i);        // only interested in other non-root views        if (focusable == focused || focusable == root) continue;        // get focus bounds of other view in same coordinate system        focusable.getFocusedRect(mOtherRect);        root.offsetDescendantRectToMyCoords(focusable, mOtherRect);        if (isBetterCandidate(direction, focusedRect, mOtherRect, mBestCandidateRect)) {            mBestCandidateRect.set(mOtherRect);            closest = focusable;        }    }    return closest;}

focusable存储所有可获取焦点控件，遍历focusable，root.offsetDescendantRectToMyCoords()方法把控件置于root的坐标系中，然后通过isBetterCandidate()方法选出最优控件。

isBetterCandidate()方法的流程：

isCandidate()方法判断是否在source对应的方向上

beamBeats()方法判断rect1是否优于rect2,比较从三个维度展开：

是否有重叠
rect1有重叠，rect2无重叠，再从rect2是否完全在source的对应方向上。比如direction为FOCUS_LEFT,rect2.right<=source.left表示rect2完全在source左边
离source在direction方向上的距离

Android(安卓)KeyEvent分发机制

Android KeyEvent分发机制

简介

分发机制分析

focusSearch流程分析

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