google推出的carboard、daydream是沒有usb介面的，調節全靠手機自身的sensor。而想gear vr這類VR眼鏡是有USB介面的，眼鏡內部是有sensor使用者調節眼鏡的，而且有觸屏、返回鍵和音量調節鍵。是不是很像一個滑鼠。

  add device 1: /dev/input/event19
  name:     "XXXX VR, Inc. x HID"
could not get driver version for /dev/input/mouse1, Not a typewriter

shell狀態下輸入getevent -l，/dev/input/mouse1確實是一個滑鼠，證明了我們的猜想。

下面我們從裝置輸入的源頭InputReader.cpp進行分析。

InputManager::InputManager(
        const sp<EventHubInterface>& eventHub,
        const sp<InputReaderPolicyInterface>& readerPolicy,
        const sp<InputDispatcherPolicyInterface>& dispatcherPolicy) {
    mDispatcher = new InputDispatcher(dispatcherPolicy);
    mReader = new InputReader(eventHub, readerPolicy, mDispatcher);
    initialize();
}
 

void InputManager::initialize() {
    mReaderThread = new InputReaderThread(mReader);
    mDispatcherThread = new InputDispatcherThread(mDispatcher);
}

status_t InputManager::start() {
    status_t result = mDispatcherThread->run("InputDispatcher", PRIORITY_URGENT_DISPLAY);
    if (result) {
        ALOGE("Could not start InputDispatcher thread due to error %d.", result);
        return result;
    }

    result = mReaderThread->run("InputReader", PRIORITY_URGENT_DISPLAY);
    if (result) {
        ALOGE("Could not start InputReader thread due to error %d.", result);

        mDispatcherThread->requestExit();
        return result;
    }

    return OK;
}
 

InputReader是由InputManager生成，同時還生成了兩個執行緒，一個用於取InputDevice輸入的資訊，一個負責分發事件

void CursorInputMapper::process(const RawEvent* rawEvent) {
    mCursorButtonAccumulator.process(rawEvent);
    mCursorMotionAccumulator.process(rawEvent);
    mCursorScrollAccumulator.process(rawEvent);

    if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {
        sync(rawEvent->when);
    }
}

void CursorInputMapper::sync(nsecs_t when) {
    ......

    // Synthesize key down from buttons if needed.
    synthesizeButtonKeys(getContext(), AKEY_EVENT_ACTION_DOWN, when, getDeviceId(), mSource,
            policyFlags, lastButtonState, currentButtonState);

    // Send motion event.
    if (downChanged || moved || scrolled || buttonsChanged) {
        int32_t metaState = mContext->getGlobalMetaState();
        int32_t buttonState = lastButtonState;
        int32_t motionEventAction;
        if (downChanged) {
            motionEventAction = down ? AMOTION_EVENT_ACTION_DOWN : AMOTION_EVENT_ACTION_UP;
        } else if (down || mPointerController == NULL) {
            motionEventAction = AMOTION_EVENT_ACTION_MOVE;
        } else {
            motionEventAction = AMOTION_EVENT_ACTION_HOVER_MOVE;
        }

        if (buttonsReleased) {
            BitSet32 released(buttonsReleased);
            while (!released.isEmpty()) {
                int32_t actionButton = BitSet32::valueForBit(released.clearFirstMarkedBit());
                buttonState &= ~actionButton;
                NotifyMotionArgs releaseArgs(when, getDeviceId(), mSource, policyFlags,
                        AMOTION_EVENT_ACTION_BUTTON_RELEASE, actionButton, 0,
                        metaState, buttonState, AMOTION_EVENT_EDGE_FLAG_NONE,
                        displayId, 1, &pointerProperties, &pointerCoords,
                        mXPrecision, mYPrecision, downTime);
                getListener()->notifyMotion(&releaseArgs);
            }
        }

        NotifyMotionArgs args(when, getDeviceId(), mSource, policyFlags,
                motionEventAction, 0, 0, metaState, currentButtonState,
                AMOTION_EVENT_EDGE_FLAG_NONE,
                displayId, 1, &pointerProperties, &pointerCoords,
                mXPrecision, mYPrecision, downTime);
        getListener()->notifyMotion(&args);

    ......
    // Synthesize key up from buttons if needed.
    synthesizeButtonKeys(getContext(), AKEY_EVENT_ACTION_UP, when, getDeviceId(), mSource,
            policyFlags, lastButtonState, currentButtonState);

    mCursorMotionAccumulator.finishSync();
    mCursorScrollAccumulator.finishSync();
}

InputReader管理著所有的InputDevice，針對不同的輸入裝置型別，對應不同的InputMapper類，滑鼠型別是CursorInputMapper類，Cursor取事件的方法是process，在sync方法中進行處理。

static void synthesizeButtonKey(InputReaderContext* context, int32_t action,
        nsecs_t when, int32_t deviceId, uint32_t source,
        uint32_t policyFlags, int32_t lastButtonState, int32_t currentButtonState,
        int32_t buttonState, int32_t keyCode) {
    if (
            (action == AKEY_EVENT_ACTION_DOWN
                    && !(lastButtonState & buttonState)
                    && (currentButtonState & buttonState))
            || (action == AKEY_EVENT_ACTION_UP
                    && (lastButtonState & buttonState)
                    && !(currentButtonState & buttonState))) {
        NotifyKeyArgs args(when, deviceId, source, policyFlags,
                action, 0, keyCode, 0, context->getGlobalMetaState(), when);
        context->getListener()->notifyKey(&args);
    }
}

static void synthesizeButtonKeys(InputReaderContext* context, int32_t action,
        nsecs_t when, int32_t deviceId, uint32_t source,
        uint32_t policyFlags, int32_t lastButtonState, int32_t currentButtonState) {
    synthesizeButtonKey(context, action, when, deviceId, source, policyFlags,
            lastButtonState, currentButtonState,
            AMOTION_EVENT_BUTTON_BACK, AKEYCODE_BACK);
    synthesizeButtonKey(context, action, when, deviceId, source, policyFlags,
            lastButtonState, currentButtonState,
            AMOTION_EVENT_BUTTON_FORWARD, AKEYCODE_FORWARD);
}

synthesizeButtonKeys對key進行合成，我們看到了熟悉的BACK鍵，context->getListener()->notifyKey(&key)

InputManager::InputManager(
        const sp<EventHubInterface>& eventHub,
        const sp<InputReaderPolicyInterface>& readerPolicy,
        const sp<InputDispatcherPolicyInterface>& dispatcherPolicy) {
    mDispatcher = new InputDispatcher(dispatcherPolicy);

void InputDispatcher::notifyKey(const NotifyKeyArgs* args) {
......
    int32_t keyCode = args->keyCode;
    if (metaState & AMETA_META_ON && args->action == AKEY_EVENT_ACTION_DOWN) {
        int32_t newKeyCode = AKEYCODE_UNKNOWN;
        if (keyCode == AKEYCODE_DEL) {
            newKeyCode = AKEYCODE_BACK;
        } else if (keyCode == AKEYCODE_ENTER) {
            newKeyCode = AKEYCODE_HOME;
        }
        if (newKeyCode != AKEYCODE_UNKNOWN) {
            AutoMutex _l(mLock);
            struct KeyReplacement replacement = {keyCode, args->deviceId};
            mReplacedKeys.add(replacement, newKeyCode);
            keyCode = newKeyCode;
            metaState &= ~AMETA_META_ON;
        }
    } else if (args->action == AKEY_EVENT_ACTION_UP) {
        // In order to maintain a consistent stream of up and down events, check to see if the key
        // going up is one we've replaced in a down event and haven't yet replaced in an up event,
        // even if the modifier was released between the down and the up events.
        AutoMutex _l(mLock);
        struct KeyReplacement replacement = {keyCode, args->deviceId};
        ssize_t index = mReplacedKeys.indexOfKey(replacement);
        if (index >= 0) {
            keyCode = mReplacedKeys.valueAt(index);
            mReplacedKeys.removeItemsAt(index);
            metaState &= ~AMETA_META_ON;
        }
    }

    KeyEvent event;
    event.initialize(args->deviceId, args->source, args->action,
            flags, keyCode, args->scanCode, metaState, 0,
            args->downTime, args->eventTime);

    mPolicy->interceptKeyBeforeQueueing(&event, /*byref*/ policyFlags);

  .......
}

context->getListener()取得的是針對InputDispatcher的一個封裝，呼叫的是它的notifyKey，在InputManager構造方法中將InputDispatcher傳給了InputReader。實際上呼叫的是

sp<InputDispatcherPolicyInterface>

void NativeInputManager::interceptKeyBeforeQueueing(const KeyEvent* keyEvent,
        uint32_t& policyFlags) {
......
        if (keyEventObj) {
            wmActions = env->CallIntMethod(mServiceObj,
                    gServiceClassInfo.interceptKeyBeforeQueueing,
                    keyEventObj, policyFlags);
            if (checkAndClearExceptionFromCallback(env, "interceptKeyBeforeQueueing")) {
                wmActions = 0;
            }
            android_view_KeyEvent_recycle(env, keyEventObj);
            env->DeleteLocalRef(keyEventObj);
        } else {
            ALOGE("Failed to obtain key event object for interceptKeyBeforeQueueing.");
            wmActions = 0;
        }

        handleInterceptActions(wmActions, when, /*byref*/ policyFlags);
    } else {
        if (interactive) {
            policyFlags |= POLICY_FLAG_PASS_TO_USER;
        }
    }
}

sp<InputDispatcherPolicyInterface>的interceptKeyBeforeQueueing。InputManagerService的jni部分實現了InputDispatcherPolicyInterface的介面，jni部分呼叫了InputManagerService.java的interceptKeyBeforeQueueing方法，這樣key事件傳遞到了Java世界。

    private int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
        return mWindowManagerCallbacks.interceptKeyBeforeQueueing(event, policyFlags);
    }

    public interface WindowManagerCallbacks {
        public void notifyConfigurationChanged();

        public void notifyLidSwitchChanged(long whenNanos, boolean lidOpen);

        public void notifyCameraLensCoverSwitchChanged(long whenNanos, boolean lensCovered);

        public void notifyInputChannelBroken(InputWindowHandle inputWindowHandle);

        public long notifyANR(InputApplicationHandle inputApplicationHandle,
                InputWindowHandle inputWindowHandle, String reason);

        public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags);

        public int interceptMotionBeforeQueueingNonInteractive(long whenNanos, int policyFlags);

        public long interceptKeyBeforeDispatching(InputWindowHandle focus,
                KeyEvent event, int policyFlags);

        public KeyEvent dispatchUnhandledKey(InputWindowHandle focus,
                KeyEvent event, int policyFlags);

        public int getPointerLayer();
    }

package com.android.server.wm;

final class InputMonitor implements InputManagerService.WindowManagerCallbacks

key事件通過mWindowManagerCallbacks.interceptKeyBeforeQueueing傳遞，mWindowManagerCallbacks是InputMonitor的物件，InputMonitor是wm包裡的一個類，我們離windowManagerService已經很近了。

private final WindowManagerService mService;

    @Override
    public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
        return mService.mPolicy.interceptKeyBeforeQueueing(event, policyFlags);
    }

mService就是WindowManagerService，mPolicy 就是PhoneWindowManager，最終我們來到了key值的處理和分發樞紐。

    @Override
    public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
        if (!mSystemBooted) {
            // If we have not yet booted, don't let key events do anything.
            return 0;
        }

        final boolean interactive = (policyFlags & FLAG_INTERACTIVE) != 0;
        final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;
        final boolean canceled = event.isCanceled();
        final int keyCode = event.getKeyCode();

        final boolean isInjected = (policyFlags & WindowManagerPolicy.FLAG_INJECTED) != 0;

        ......
        switch (keyCode) {
            case KeyEvent.KEYCODE_BACK: {
                if (down) {
                    mBackKeyHandled = false;
                    if (hasLongPressOnBackBehavior()) {
                        Message msg = mHandler.obtainMessage(MSG_BACK_LONG_PRESS);
                        msg.setAsynchronous(true);
                        mHandler.sendMessageDelayed(msg,
                                ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
                    }
                } else {
                    boolean handled = mBackKeyHandled;

                    // Reset back key state
                    cancelPendingBackKeyAction();

                    // Don't pass back press to app if we've already handled it
                    if (handled) {
                        result &= ~ACTION_PASS_TO_USER;
                    }
                }
                break;
            }

           ......

        if (useHapticFeedback) {
            performHapticFeedbackLw(null, HapticFeedbackConstants.VIRTUAL_KEY, false);
        }

        if (isWakeKey) {
            wakeUp(event.getEventTime(), mAllowTheaterModeWakeFromKey, "android.policy:KEY");
        }

        return result;
    }

PhoneWindowManager對BACK按鍵的處理並沒有什麼特別的，PhoneWindowManager主要是對全域性性的key進行處理，比如POWER、RECENT等，由於BACK按鍵對於View體系是非常重要的，事件肯定會分發到View層面進行進一步處理。把Key事件放進佇列，我們回到InputDispatcher.cpp。

void InputDispatcher::notifyKey(const NotifyKeyArgs* args) {
......
    mPolicy->interceptKeyBeforeQueueing(&event, /*byref*/ policyFlags);

    bool needWake;
    { // acquire lock
        mLock.lock();

        if (shouldSendKeyToInputFilterLocked(args)) {
            mLock.unlock();

            policyFlags |= POLICY_FLAG_FILTERED;
            if (!mPolicy->filterInputEvent(&event, policyFlags)) {
                return; // event was consumed by the filter
            }

            mLock.lock();
        }

        int32_t repeatCount = 0;
        KeyEntry* newEntry = new KeyEntry(args->eventTime,
                args->deviceId, args->source, policyFlags,
                args->action, flags, keyCode, args->scanCode,
                metaState, repeatCount, args->downTime);

        needWake = enqueueInboundEventLocked(newEntry);
        mLock.unlock();
    } // release lock

    if (needWake) {
        mLooper->wake();
    }
}

將Key事件放進佇列，然後呢？mLooper->wake()消費這個訊息，不理解的可以看NativeMessageQueue

bool InputDispatcher::enqueueInboundEventLocked(EventEntry* entry) {
    bool needWake = mInboundQueue.isEmpty();
    mInboundQueue.enqueueAtTail(entry);
    traceInboundQueueLengthLocked();

InputDispatcher的enqueueInboundEventLocked方法將事件放進佇列。

void InputReader::loopOnce() {
    ......

    // Send out a message that the describes the changed input devices.
    if (inputDevicesChanged) {
        mPolicy->notifyInputDevicesChanged(inputDevices);
    }

    // Flush queued events out to the listener.
    // This must happen outside of the lock because the listener could potentially call
    // back into the InputReader's methods, such as getScanCodeState, or become blocked
    // on another thread similarly waiting to acquire the InputReader lock thereby
    // resulting in a deadlock.  This situation is actually quite plausible because the
    // listener is actually the input dispatcher, which calls into the window manager,
    // which occasionally calls into the input reader.
    mQueuedListener->flush();
}

bool InputDispatcherThread::threadLoop() {
    mDispatcher->dispatchOnce();
    return true;
}

void InputDispatcher::dispatchOnce() {
    nsecs_t nextWakeupTime = LONG_LONG_MAX;
    { // acquire lock
        AutoMutex _l(mLock);
        mDispatcherIsAliveCondition.broadcast();

        // Run a dispatch loop if there are no pending commands.
        // The dispatch loop might enqueue commands to run afterwards.
        if (!haveCommandsLocked()) {
            dispatchOnceInnerLocked(&nextWakeupTime);
        }

        // Run all pending commands if there are any.
        // If any commands were run then force the next poll to wake up immediately.
        if (runCommandsLockedInterruptible()) {
            nextWakeupTime = LONG_LONG_MIN;
        }
    } // release lock

    // Wait for callback or timeout or wake.  (make sure we round up, not down)
    nsecs_t currentTime = now();
    int timeoutMillis = toMillisecondTimeoutDelay(currentTime, nextWakeupTime);
    mLooper->pollOnce(timeoutMillis);
}

void InputDispatcher::dispatchOnceInnerLocked(nsecs_t* nextWakeupTime) {
    ......
            // Inbound queue has at least one entry.
            mPendingEvent = mInboundQueue.dequeueAtHead();
            traceInboundQueueLengthLocked();
    ......
    case EventEntry::TYPE_KEY: {
        KeyEntry* typedEntry = static_cast<KeyEntry*>(mPendingEvent);
        if (isAppSwitchDue) {
            if (isAppSwitchKeyEventLocked(typedEntry)) {
                resetPendingAppSwitchLocked(true);
                isAppSwitchDue = false;
            } else if (dropReason == DROP_REASON_NOT_DROPPED) {
                dropReason = DROP_REASON_APP_SWITCH;
            }
        }
        if (dropReason == DROP_REASON_NOT_DROPPED
                && isStaleEventLocked(currentTime, typedEntry)) {
            dropReason = DROP_REASON_STALE;
        }
        if (dropReason == DROP_REASON_NOT_DROPPED && mNextUnblockedEvent) {
            dropReason = DROP_REASON_BLOCKED;
        }
        done = dispatchKeyLocked(currentTime, typedEntry, &dropReason, nextWakeupTime);
        break;
    }
    ......
}

void InputDispatcher::dispatchEventLocked(nsecs_t currentTime,
        EventEntry* eventEntry, const Vector<InputTarget>& inputTargets) {
......

    for (size_t i = 0; i < inputTargets.size(); i++) {
        const InputTarget& inputTarget = inputTargets.itemAt(i);

        ssize_t connectionIndex = getConnectionIndexLocked(inputTarget.inputChannel);
        if (connectionIndex >= 0) {
            sp<Connection> connection = mConnectionsByFd.valueAt(connectionIndex);
            prepareDispatchCycleLocked(currentTime, connection, eventEntry, &inputTarget);
......
}

void InputDispatcher::startDispatchCycleLocked(nsecs_t currentTime,
        const sp<Connection>& connection) {
......
    while (connection->status == Connection::STATUS_NORMAL
            && !connection->outboundQueue.isEmpty()) {
        DispatchEntry* dispatchEntry = connection->outboundQueue.head;
        dispatchEntry->deliveryTime = currentTime;

        // Publish the event.
        status_t status;
        EventEntry* eventEntry = dispatchEntry->eventEntry;
        switch (eventEntry->type) {
        case EventEntry::TYPE_KEY: {
            KeyEntry* keyEntry = static_cast<KeyEntry*>(eventEntry);

            // Publish the key event.
            status = connection->inputPublisher.publishKeyEvent(dispatchEntry->seq,
                    keyEntry->deviceId, keyEntry->source,
                    dispatchEntry->resolvedAction, dispatchEntry->resolvedFlags,
                    keyEntry->keyCode, keyEntry->scanCode,
                    keyEntry->metaState, keyEntry->repeatCount, keyEntry->downTime,
                    keyEntry->eventTime);
            break;
        }

之前我們介紹InputReader建立的時候，提到了InputManager建立了兩個執行緒，一個是分發執行緒，一個是取事件的執行緒，在start中啟動了他們，會呼叫到InputReader的loopOnce取得事件放入佇列，放入佇列的預處理之前已經分析，接下來是InputDispatcherThread循壞mDispatcher->dispatchOnce。dispatchOnce中dispatch一個訊息

status_t InputPublisher::publishKeyEvent(
        uint32_t seq,
        int32_t deviceId,
        int32_t source,
        int32_t action,
        int32_t flags,
        int32_t keyCode,
        int32_t scanCode,
        int32_t metaState,
        int32_t repeatCount,
        nsecs_t downTime,
        nsecs_t eventTime) {
.....
    InputMessage msg;
    msg.header.type = InputMessage::TYPE_KEY;
    msg.body.key.seq = seq;
    msg.body.key.deviceId = deviceId;
    msg.body.key.source = source;
    msg.body.key.action = action;
    msg.body.key.flags = flags;
    msg.body.key.keyCode = keyCode;
    msg.body.key.scanCode = scanCode;
    msg.body.key.metaState = metaState;
    msg.body.key.repeatCount = repeatCount;
    msg.body.key.downTime = downTime;
    msg.body.key.eventTime = eventTime;
    return mChannel->sendMessage(&msg);
}

最終在InputPublisher中由mChannel->sendMessage, mChannel是某個window和InputReader的一個橋樑，這裡發訊息應該是發給了一個window。

 class Connection : public RefBase {
    protected:
        virtual ~Connection();

    public:
        enum Status {
            // Everything is peachy.
            STATUS_NORMAL,
            // An unrecoverable communication error has occurred.
            STATUS_BROKEN,
            // The input channel has been unregistered.
            STATUS_ZOMBIE
        };

        Status status;
        sp<InputChannel> inputChannel; // never null
        sp<InputWindowHandle> inputWindowHandle; // may be null
        bool monitor;
        InputPublisher inputPublisher;
        InputState inputState;

        // True if the socket is full and no further events can be published until
        // the application consumes some of the input.
        bool inputPublisherBlocked;

        // Queue of events that need to be published to the connection.
        Queue<DispatchEntry> outboundQueue;

        // Queue of events that have been published to the connection but that have not
        // yet received a "finished" response from the application.
        Queue<DispatchEntry> waitQueue;

        explicit Connection(const sp<InputChannel>& inputChannel,
                const sp<InputWindowHandle>& inputWindowHandle, bool monitor);

        inline const char* getInputChannelName() const { return inputChannel->getName().string(); }

        const char* getWindowName() const;
        const char* getStatusLabel() const;

        DispatchEntry* findWaitQueueEntry(uint32_t seq);
    };

Connection是InputDispatcher的一個內部類，通過registerInputChannel，那麼在哪裡建立了這種連線呢？

status_t NativeInputManager::registerInputChannel(JNIEnv* /* env */,
        const sp<InputChannel>& inputChannel,
        const sp<InputWindowHandle>& inputWindowHandle, bool monitor) {
    return mInputManager->getDispatcher()->registerInputChannel(
            inputChannel, inputWindowHandle, monitor);
}

    public void registerInputChannel(InputChannel inputChannel,
            InputWindowHandle inputWindowHandle) {
        if (inputChannel == null) {
            throw new IllegalArgumentException("inputChannel must not be null.");
        }

        nativeRegisterInputChannel(mPtr, inputChannel, inputWindowHandle, false);
    }

我找找到了InputManagerService.java這個源頭

    void openInputChannel(InputChannel outInputChannel) {
        if (mInputChannel != null) {
            throw new IllegalStateException("Window already has an input channel.");
        }
        String name = makeInputChannelName();
        InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
        mInputChannel = inputChannels[0];
        mClientChannel = inputChannels[1];
        mInputWindowHandle.inputChannel = inputChannels[0];
        if (outInputChannel != null) {
            mClientChannel.transferTo(outInputChannel);
            mClientChannel.dispose();
            mClientChannel = null;
        } else {
            // If the window died visible, we setup a dummy input channel, so that taps
            // can still detected by input monitor channel, and we can relaunch the app.
            // Create dummy event receiver that simply reports all events as handled.
            mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
        }
        mService.mInputManager.registerInputChannel(mInputChannel, mInputWindowHandle);
    }

WindowState中找到了有關呼叫，這個mService又是WindowsManagerService

    public int addWindow(Session session, IWindow client, int seq,
            WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
            Rect outContentInsets, Rect outStableInsets, Rect outOutsets,
            InputChannel outInputChannel) {
......

            final boolean openInputChannels = (outInputChannel != null
                    && (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);
            if  (openInputChannels) {
                win.openInputChannel(outInputChannel);
            }
 public View addStartingWindow(IBinder appToken, String packageName, int theme,
            CompatibilityInfo compatInfo, CharSequence nonLocalizedLabel, int labelRes,
            int icon, int logo, int windowFlags, Configuration overrideConfig) {
  ......
        WindowManager wm = null;
        View view = null;

        try {
            Context context = mContext;
            if (DEBUG_STARTING_WINDOW) Slog.d(TAG, "addStartingWindow " + packageName
                    + ": nonLocalizedLabel=" + nonLocalizedLabel + " theme="
                    + Integer.toHexString(theme));
            if (theme != context.getThemeResId() || labelRes != 0) {
                try {
                    context = context.createPackageContext(packageName, 0);
                    context.setTheme(theme);
                } catch (PackageManager.NameNotFoundException e) {
                    // Ignore
                }
            }

......

            final PhoneWindow win = new PhoneWindow(context);
......

            wm = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
            view = win.getDecorView();

            if (DEBUG_STARTING_WINDOW) Slog.d(TAG, "Adding starting window for "
                + packageName + " / " + appToken + ": " + (view.getParent() != null ? view : null));

            wm.addView(view, params);

......
    }

在每次addWindow的時候建立了一個連線，證實了我們的猜想。

  public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
......

        ViewRootImpl root;
        View panelParentView = null;

        synchronized (mLock) {
......
            root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
        }

        // do this last because it fires off messages to start doing things
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
......
    }

Android View體系中，Window包含了很多View, 包括一個DecorView和一個ViewGroup，之後新增進來的View，都會建立一個ViewRootImpl對應，讓我們看看ViewRootImpl是幹什麼的？

/**
 * The top of a view hierarchy, implementing the needed protocol between View
 * and the WindowManager.  This is for the most part an internal implementation
 * detail of {@link WindowManagerGlobal}.
 *
 * {@hide}
 */
@SuppressWarnings({"EmptyCatchBlock", "PointlessBooleanExpression"})
public final class ViewRootImpl implements ViewParent,
        View.AttachInfo.Callbacks, ThreadedRenderer.HardwareDrawCallbacks 

ViewRootImpl是WindowManager和View之間的橋樑，管理著View除檢視外其他的部分，它實際上是一個Handler，它可以向DecorView分發事件，當然，AccessibilityService的部分也在這裡處理。

setView(View view...){

......

                if (mInputChannel != null) {
                    if (mInputQueueCallback != null) {
                        mInputQueue = new InputQueue();
                        mInputQueueCallback.onInputQueueCreated(mInputQueue);
                    }
                    mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
                            Looper.myLooper());
                }
......
}

ViewRootImpl setView的時候會建立一個InputReceiver，當有inputEvent時觸發。

    final class WindowInputEventReceiver extends InputEventReceiver {
        public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
            super(inputChannel, looper);
        }

        @Override
        public void onInputEvent(InputEvent event) {
            enqueueInputEvent(event, this, 0, true);
        }

        @Override
        public void onBatchedInputEventPending() {
            if (mUnbufferedInputDispatch) {
                super.onBatchedInputEventPending();
            } else {
                scheduleConsumeBatchedInput();
            }
        }

        @Override
        public void dispose() {
            unscheduleConsumeBatchedInput();
            super.dispose();
        }
    }

void enqueueInputEvent(InputEvent event,
            InputEventReceiver receiver, int flags, boolean processImmediately) {
......

        if (processImmediately) {
            doProcessInputEvents();
        } else {
            scheduleProcessInputEvents();
        }
    }

    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;

  ......

            deliverInputEvent(q);
        }

......
    }

    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);
        }
    }

        public boolean shouldSkipIme() {
            if ((mFlags & FLAG_DELIVER_POST_IME) != 0) {
                return true;
            }
            return mEvent instanceof MotionEvent
                    && mEvent.isFromSource(InputDevice.SOURCE_CLASS_POINTER);
        }

 mFirstInputStage = earlyPostInputStage;

這個stage很關鍵，shouldSkipIme返回true，因為沒有軟鍵盤，所以stage = earlyPostInputStage。 注意next引數是ViewPostImeInputStage，earlyPostInputStage的主要作用是將Key事件傳遞到native層的Activity(現在很多的Activity是用NativeActivity開發的)，所以我們不走這裡，我們走next.deliver，也就是ViewPostImeInputStage。

final class ViewPostImeInputStage extends InputStage {
        public ViewPostImeInputStage(InputStage next) {
            super(next);
        }

        @Override
        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);
                }
            }
        }

        @Override
        protected void onDeliverToNext(QueuedInputEvent q) {
            if (mUnbufferedInputDispatch
                    && q.mEvent instanceof MotionEvent
                    && ((MotionEvent)q.mEvent).isTouchEvent()
                    && isTerminalInputEvent(q.mEvent)) {
                mUnbufferedInputDispatch = false;
                scheduleConsumeBatchedInput();
            }
            super.onDeliverToNext(q);
        }

        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;
            }

key終於傳遞到了View hierarchy，也就是DecorView。