Android系统开发 按键事件的分发详解

前言

　　此篇博客会讲解基于Android10.0系统的按键事件(KeyEvent)分发流程，按键事件包括了设备物理按钮、遥控器、输入法、USB-OTG外接键盘等等。请注意！屏幕上的触控事件不属于按键事件。另外此篇博客不涉及Linux层。

大致架构流程

　　在说详解源代码的执行流程前，我们先用最大致的了解下按键事件的流程与设计抽象思维。

首先要搞清楚，按键事件(KeyEvent)有谁消费。按键事件的消费者其实分2大块，一个是framework层的系统操作消费，一个是View的视图操作消费。

　　framework层的系统操作消费一般有：

• 　　power键
• 　　音量键
• 　　导航键(back、home等等)
• 　　定制设备的物理键(比如音乐播放/暂停键，快进，倒退，下一步)
• 　　外接键盘上的一些按键

　　View的视图操作消费一般有：

• 　　上下左右方向键(包含遥控器与键盘)，用来TV设备上切换焦点
• 　　回车键
• 　　外接键盘与输入法等等相关其他按键，字母与数字键等等

它们都有对应的关键处理类，framework层的系统操作消费对应着PhoneWindowManager(属于系统进程)，View的视图操作消费对应着ViewRootImpl(属于应用进程)。

或许还是有一些人不明白，为什么要分2部分来处理按键事件呢？原因其实很简单，这里一一解释：

1.应用与系统的进程不一样，无法将两者结合在一起。 进程隔离是Android系统基础中的基础。

2.系统是需要消费按键实现一些系统功能的，比如音量调节、屏幕亮灭、power+音量键截图等等。

3.在应用层上，按键功能是需要传递到应用的UI层进行逻辑处理的。比如方向键与回车键，方向键其实是执行了焦点选择的事件消费，而回车键是执行了点击事件的代码onClickListener。这些都是属于应用层上的事件消费。

顺序流程

　　PhoneWindowManager与ViewRootImpl都消费按键事件，那肯定有一个先后顺序。在代码里PhoneWindowManager是先执行的ViewRootImpl是后执行的。但是有一部分人会认为PhoneWindowManager处理完后会把按键事件转给ViewRootImpl。这是错误的，疏忽一个关键，它们不是一个进程无法直接传递信息，它们也不是互相之间创建了AIDL进行了通信。而是依靠Linux层分发传递了按键事件(反正PhoneWindowManager都是依靠Linux层传上来的，ViewRootImpl在依靠Linux层传上来按键事件也是合情合理的)。所以，Linux层、PhoneWindowManager、ViewRootImpl它们的三者关系如下流程图：

 

framework层的按键事件消费

这里插一句题外话，很多framework开发会在PhoneWindowManager的interceptKeyBeforeQueueing方法实现自定义的按键功能。比如自定义实现power键的额外功能，或者其他自定义键值的按键功能，也有在这里发送全局广播给应用层app监听后实现功能。这些操作没有问题，但是请额外注意这个变量的 int result; 的返回值，因为它关系到按键事件是否分发到应用层。

 

应用层的按键事件消费

 

ViewRootImpl内部的InputStage：

InputStage 用于实现责任链中某个阶段的基类，处理输入的责任链，在调用deliver时会遍历责任链传递事件。InputStage事件分发完成后会调用finishInputEvent，告知SystemServer进程的InputDispatcher线程，最终将该事件移除，完成此次事件的分发消费。

在ViewRootImpl的setView方法中，完成了InputStage的责任链组装，代码如下：

• SyntheticInputStage。综合处理事件阶段，比如处理导航面板、操作杆等事件。

• ViewPostImeInputStage。视图输入处理阶段，比如按键、手指触摸等运动事件，我们熟知的view事件分发就发生在这个阶段。

• NativePostImeInputStage。本地方法处理阶段，主要构建了可延迟的队列。

• EarlyPostImeInputStage。输入法早期处理阶段。

• ImeInputStage。输入法事件处理阶段，处理输入法字符。

• ViewPreImeInputStage。视图预处理输入法事件阶段，调用视图view的dispatchKeyEventPreIme方法。

• NativePreImeInputStage。本地方法预处理输入法事件阶段。

InputStage 的全部代码与继承它的实现类：

    /**
     * Base class for implementing a stage in the chain of responsibility
     * for processing input events.
     * <p>
     * Events are delivered to the stage by the {@link #deliver} method.  The stage
     * then has the choice of finishing the event or forwarding it to the next stage.
     * </p>
     */
    abstract class InputStage {
        private final InputStage mNext;

        protected static final int FORWARD = 0;
        protected static final int FINISH_HANDLED = 1;
        protected static final int FINISH_NOT_HANDLED = 2;

        /**
         * Creates an input stage.
         * @param next The next stage to which events should be forwarded.
         */
        public InputStage(InputStage next) {
            mNext = next;
        }

        /**
         * Delivers an event to be processed.
         */
        public final void deliver(QueuedInputEvent q) {
            /// M: [ANR] Add for monitoring stage status. {
            ViewDebugManager.getInstance().debugInputStageDeliverd(this,
                    System.currentTimeMillis());
            /// }
            if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {
                forward(q);
            } else if (shouldDropInputEvent(q)) {
                finish(q, false);
            } else {
                ViewDebugManager.getInstance().debugInputDispatchState(q.mEvent, this.toString());
                apply(q, onProcess(q));
            }
        }

        /**
         * Marks the the input event as finished then forwards it to the next stage.
         */
        protected void finish(QueuedInputEvent q, boolean handled) {
            q.mFlags |= QueuedInputEvent.FLAG_FINISHED;
            if (handled) {
                q.mFlags |= QueuedInputEvent.FLAG_FINISHED_HANDLED;
            }
            forward(q);
        }

        /**
         * Forwards the event to the next stage.
         */
        protected void forward(QueuedInputEvent q) {
            onDeliverToNext(q);
        }

        /**
         * Applies a result code from {@link #onProcess} to the specified event.
         */
        protected void apply(QueuedInputEvent q, int result) {
            if (result == FORWARD) {
                forward(q);
            } else if (result == FINISH_HANDLED) {
                finish(q, true);
            } else if (result == FINISH_NOT_HANDLED) {
                finish(q, false);
            } else {
                throw new IllegalArgumentException("Invalid result: " + result);
            }
        }

        /**
         * Called when an event is ready to be processed.
         * @return A result code indicating how the event was handled.
         */
        protected int onProcess(QueuedInputEvent q) {
            return FORWARD;
        }

        /**
         * Called when an event is being delivered to the next stage.
         */
        protected void onDeliverToNext(QueuedInputEvent q) {
            if (DEBUG_INPUT_STAGES) {
                Log.v(mTag, "Done with " + getClass().getSimpleName() + ". " + q);
            }
            if (mNext != null) {
                mNext.deliver(q);
            } else {
                finishInputEvent(q);
            }
        }

        protected void onWindowFocusChanged(boolean hasWindowFocus) {
            if (mNext != null) {
                mNext.onWindowFocusChanged(hasWindowFocus);
            }
        }

        protected void onDetachedFromWindow() {
            if (mNext != null) {
                mNext.onDetachedFromWindow();
            }
        }

        protected boolean shouldDropInputEvent(QueuedInputEvent q) {
            if (mView == null || !mAdded) {
                Slog.w(mTag, "Dropping event due to root view being removed: " + q.mEvent);
                return true;
            } else if ((!mAttachInfo.mHasWindowFocus
                    && !q.mEvent.isFromSource(InputDevice.SOURCE_CLASS_POINTER)
                    && !isAutofillUiShowing()) || mStopped
                    || (mIsAmbientMode && !q.mEvent.isFromSource(InputDevice.SOURCE_CLASS_BUTTON))
                    || (mPausedForTransition && !isBack(q.mEvent))) {
                // This is a focus event and the window doesn't currently have input focus or
                // has stopped. This could be an event that came back from the previous stage
                // but the window has lost focus or stopped in the meantime.
                if (isTerminalInputEvent(q.mEvent)) {
                    // Don't drop terminal input events, however mark them as canceled.
                    q.mEvent.cancel();
                    Slog.w(mTag, "Cancelling event due to no window focus: " + q.mEvent);
                    return false;
                }

                // Drop non-terminal input events.
                Slog.w(mTag, "Dropping event due to no window focus: " + q.mEvent);
                return true;
            }
            return false;
        }

        void dump(String prefix, PrintWriter writer) {
            if (mNext != null) {
                mNext.dump(prefix, writer);
            }
        }

        private boolean isBack(InputEvent event) {
            if (event instanceof KeyEvent) {
                return ((KeyEvent) event).getKeyCode() == KeyEvent.KEYCODE_BACK;
            } else {
                return false;
            }
        }
    }

    /**
     * Base class for implementing an input pipeline stage that supports
     * asynchronous and out-of-order processing of input events.
     * <p>
     * In addition to what a normal input stage can do, an asynchronous
     * input stage may also defer an input event that has been delivered to it
     * and finish or forward it later.
     * </p>
     */
    abstract class AsyncInputStage extends InputStage {
        private final String mTraceCounter;

        private QueuedInputEvent mQueueHead;
        private QueuedInputEvent mQueueTail;
        private int mQueueLength;

        protected static final int DEFER = 3;

        /**
         * Creates an asynchronous input stage.
         * @param next The next stage to which events should be forwarded.
         * @param traceCounter The name of a counter to record the size of
         * the queue of pending events.
         */
        public AsyncInputStage(InputStage next, String traceCounter) {
            super(next);
            mTraceCounter = traceCounter;
        }

        /**
         * Marks the event as deferred, which is to say that it will be handled
         * asynchronously.  The caller is responsible for calling {@link #forward}
         * or {@link #finish} later when it is done handling the event.
         */
        protected void defer(QueuedInputEvent q) {
            q.mFlags |= QueuedInputEvent.FLAG_DEFERRED;
            enqueue(q);
        }

        @Override
        protected void forward(QueuedInputEvent q) {
            // Clear the deferred flag.
            q.mFlags &= ~QueuedInputEvent.FLAG_DEFERRED;

            // Fast path if the queue is empty.
            QueuedInputEvent curr = mQueueHead;
            if (curr == null) {
                super.forward(q);
                return;
            }

            // Determine whether the event must be serialized behind any others
            // before it can be delivered to the next stage.  This is done because
            // deferred events might be handled out of order by the stage.
            final int deviceId = q.mEvent.getDeviceId();
            QueuedInputEvent prev = null;
            boolean blocked = false;
            while (curr != null && curr != q) {
                if (!blocked && deviceId == curr.mEvent.getDeviceId()) {
                    blocked = true;
                }
                prev = curr;
                curr = curr.mNext;
            }

            // If the event is blocked, then leave it in the queue to be delivered later.
            // Note that the event might not yet be in the queue if it was not previously
            // deferred so we will enqueue it if needed.
            if (blocked) {
                if (curr == null) {
                    enqueue(q);
                }
                return;
            }

            // The event is not blocked.  Deliver it immediately.
            if (curr != null) {
                curr = curr.mNext;
                dequeue(q, prev);
            }
            super.forward(q);

            // Dequeuing this event may have unblocked successors.  Deliver them.
            while (curr != null) {
                if (deviceId == curr.mEvent.getDeviceId()) {
                    if ((curr.mFlags & QueuedInputEvent.FLAG_DEFERRED) != 0) {
                        break;
                    }
                    QueuedInputEvent next = curr.mNext;
                    dequeue(curr, prev);
                    super.forward(curr);
                    curr = next;
                } else {
                    prev = curr;
                    curr = curr.mNext;
                }
            }
        }

        @Override
        protected void apply(QueuedInputEvent q, int result) {
            if (result == DEFER) {
                defer(q);
            } else {
                super.apply(q, result);
            }
        }

        private void enqueue(QueuedInputEvent q) {
            if (mQueueTail == null) {
                mQueueHead = q;
                mQueueTail = q;
            } else {
                mQueueTail.mNext = q;
                mQueueTail = q;
            }

            mQueueLength += 1;
            Trace.traceCounter(Trace.TRACE_TAG_INPUT, mTraceCounter, mQueueLength);
        }

        private void dequeue(QueuedInputEvent q, QueuedInputEvent prev) {
            if (prev == null) {
                mQueueHead = q.mNext;
            } else {
                prev.mNext = q.mNext;
            }
            if (mQueueTail == q) {
                mQueueTail = prev;
            }
            q.mNext = null;

            mQueueLength -= 1;
            Trace.traceCounter(Trace.TRACE_TAG_INPUT, mTraceCounter, mQueueLength);
        }

        @Override
        void dump(String prefix, PrintWriter writer) {
            writer.print(prefix);
            writer.print(getClass().getName());
            writer.print(": mQueueLength=");
            writer.println(mQueueLength);

            super.dump(prefix, writer);
        }
    }

    /**
     * Delivers pre-ime input events to a native activity.
     * Does not support pointer events.
     */
    final class NativePreImeInputStage extends AsyncInputStage
            implements InputQueue.FinishedInputEventCallback {
        public NativePreImeInputStage(InputStage next, String traceCounter) {
            super(next, traceCounter);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            if (mInputQueue != null && q.mEvent instanceof KeyEvent) {
                mInputQueue.sendInputEvent(q.mEvent, q, true, this);
                return DEFER;
            }
            return FORWARD;
        }

        @Override
        public void onFinishedInputEvent(Object token, boolean handled) {
            QueuedInputEvent q = (QueuedInputEvent)token;
            if (handled) {
                finish(q, true);
                return;
            }
            forward(q);
        }
    }

    /**
     * Delivers pre-ime input events to the view hierarchy.
     * Does not support pointer events.
     */
    final class ViewPreImeInputStage extends InputStage {
        public ViewPreImeInputStage(InputStage next) {
            super(next);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            if (q.mEvent instanceof KeyEvent) {
                return processKeyEvent(q);
            }
            return FORWARD;
        }

        private int processKeyEvent(QueuedInputEvent q) {
            final KeyEvent event = (KeyEvent)q.mEvent;
            if (mView.dispatchKeyEventPreIme(event)) {
                return FINISH_HANDLED;
            }
            return FORWARD;
        }
    }

    /**
     * Delivers input events to the ime.
     * Does not support pointer events.
     */
    final class ImeInputStage extends AsyncInputStage
            implements InputMethodManager.FinishedInputEventCallback {
        public ImeInputStage(InputStage next, String traceCounter) {
            super(next, traceCounter);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            if (mLastWasImTarget && !isInLocalFocusMode()) {
                InputMethodManager imm = mContext.getSystemService(InputMethodManager.class);
                if (imm != null) {
                    final InputEvent event = q.mEvent;
                    if (DEBUG_IMF) Log.v(mTag, "Sending input event to IME: " + event);
                    int result = imm.dispatchInputEvent(event, q, this, mHandler);
                    if (result == InputMethodManager.DISPATCH_HANDLED) {
                        return FINISH_HANDLED;
                    } else if (result == InputMethodManager.DISPATCH_NOT_HANDLED) {
                        // The IME could not handle it, so skip along to the next InputStage
                        return FORWARD;
                    } else {
                        return DEFER; // callback will be invoked later
                    }
                }
            }
            return FORWARD;
        }

        @Override
        public void onFinishedInputEvent(Object token, boolean handled) {
            QueuedInputEvent q = (QueuedInputEvent)token;
            if (DEBUG_IMF || ViewDebugManager.DEBUG_INPUT || ViewDebugManager.DEBUG_KEY) {
                Log.d(mTag, "IME finishedEvent: handled = " + handled + ", event = " + q
                        + ", viewAncestor = " + this);
            }
            if (handled) {
                finish(q, true);
                return;
            }
            forward(q);
        }
    }

    /**
     * Performs early processing of post-ime input events.
     */
    final class EarlyPostImeInputStage extends InputStage {
        public EarlyPostImeInputStage(InputStage next) {
            super(next);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            if (q.mEvent instanceof KeyEvent) {
                return processKeyEvent(q);
            } else if (q.mEvent instanceof MotionEvent) {
                return processMotionEvent(q);
            }
            return FORWARD;
        }

        private int processKeyEvent(QueuedInputEvent q) {
            final KeyEvent event = (KeyEvent)q.mEvent;

            if (mAttachInfo.mTooltipHost != null) {
                mAttachInfo.mTooltipHost.handleTooltipKey(event);
            }

            // If the key's purpose is to exit touch mode then we consume it
            // and consider it handled.
            if (checkForLeavingTouchModeAndConsume(event)) {
                return FINISH_HANDLED;
            }

            // Make sure the fallback event policy sees all keys that will be
            // delivered to the view hierarchy.
            mFallbackEventHandler.preDispatchKeyEvent(event);
            return FORWARD;
        }

        private int processMotionEvent(QueuedInputEvent q) {
            final MotionEvent event = (MotionEvent) q.mEvent;

            if (event.isFromSource(InputDevice.SOURCE_CLASS_POINTER)) {
                return processPointerEvent(q);
            }

            // If the motion event is from an absolute position device, exit touch mode
            final int action = event.getActionMasked();
            if (action == MotionEvent.ACTION_DOWN || action == MotionEvent.ACTION_SCROLL) {
                if (event.isFromSource(InputDevice.SOURCE_CLASS_POSITION)) {
                    ensureTouchMode(false);
                }
            }
            return FORWARD;
        }

        private int processPointerEvent(QueuedInputEvent q) {
            final MotionEvent event = (MotionEvent)q.mEvent;

            // Translate the pointer event for compatibility, if needed.
            if (mTranslator != null) {
                mTranslator.translateEventInScreenToAppWindow(event);
            }

            // Enter touch mode on down or scroll, if it is coming from a touch screen device,
            // exit otherwise.
            final int action = event.getAction();
            if (action == MotionEvent.ACTION_DOWN || action == MotionEvent.ACTION_SCROLL) {
                ensureTouchMode(event.isFromSource(InputDevice.SOURCE_TOUCHSCREEN));
            }

            if (action == MotionEvent.ACTION_DOWN) {
                // Upon motion event within app window, close autofill ui.
                AutofillManager afm = getAutofillManager();
                if (afm != null) {
                    afm.requestHideFillUi();
                }
            }

            if (action == MotionEvent.ACTION_DOWN && mAttachInfo.mTooltipHost != null) {
                mAttachInfo.mTooltipHost.hideTooltip();
            }

            // Offset the scroll position.
            if (mCurScrollY != 0) {
                event.offsetLocation(0, mCurScrollY);
            }

            // Remember the touch position for possible drag-initiation.
            if (event.isTouchEvent()) {
                mLastTouchPoint.x = event.getRawX();
                mLastTouchPoint.y = event.getRawY();
                mLastTouchSource = event.getSource();
            }
            return FORWARD;
        }
    }

    /**
     * Delivers post-ime input events to a native activity.
     */
    final class NativePostImeInputStage extends AsyncInputStage
            implements InputQueue.FinishedInputEventCallback {
        public NativePostImeInputStage(InputStage next, String traceCounter) {
            super(next, traceCounter);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            if (mInputQueue != null) {
                mInputQueue.sendInputEvent(q.mEvent, q, false, this);
                return DEFER;
            }
            return FORWARD;
        }

        @Override
        public void onFinishedInputEvent(Object token, boolean handled) {
            QueuedInputEvent q = (QueuedInputEvent)token;
            if (handled) {
                finish(q, true);
                return;
            }
            forward(q);
        }
    }

    /**
     * Delivers post-ime input events to the view hierarchy.
     */
    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 boolean performFocusNavigation(KeyEvent event) {
            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 true;
                        }
                    }

                    // Give the focused view a last chance to handle the dpad key.
                    if (mView.dispatchUnhandledMove(focused, direction)) {
                        return true;
                    }
                } else {
                    if (mView.restoreDefaultFocus()) {
                        return true;
                    }
                }
            }
            return false;
        }

        private boolean performKeyboardGroupNavigation(int direction) {
            final View focused = mView.findFocus();
            if (focused == null && mView.restoreDefaultFocus()) {
                return true;
            }
            View cluster = focused == null ? keyboardNavigationClusterSearch(null, direction)
                    : focused.keyboardNavigationClusterSearch(null, direction);

            // Since requestFocus only takes "real" focus directions (and therefore also
            // restoreFocusInCluster), convert forward/backward focus into FOCUS_DOWN.
            int realDirection = direction;
            if (direction == View.FOCUS_FORWARD || direction == View.FOCUS_BACKWARD) {
                realDirection = View.FOCUS_DOWN;
            }

            if (cluster != null && cluster.isRootNamespace()) {
                // the default cluster. Try to find a non-clustered view to focus.
                if (cluster.restoreFocusNotInCluster()) {
                    playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));
                    return true;
                }
                // otherwise skip to next actual cluster
                cluster = keyboardNavigationClusterSearch(null, direction);
            }

            if (cluster != null && cluster.restoreFocusInCluster(realDirection)) {
                playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));
                return true;
            }

            return false;
        }

        private int processKeyEvent(QueuedInputEvent q) {
            final KeyEvent event = (KeyEvent)q.mEvent;

            if (mUnhandledKeyManager.preViewDispatch(event)) {
                if (ViewDebugManager.DEBUG_ENG) {
                    Log.v(mTag, "App handle dispatchUnique event = " + event + ", mView = " + mView
                            + ", this = " + this);
                }

                return FINISH_HANDLED;
            }

            // Deliver the key to the view hierarchy.
            if (mView.dispatchKeyEvent(event)) {
                if (ViewDebugManager.DEBUG_ENG) {
                    Log.v(mTag, "App handle key event: event = " + event + ", mView = " + mView
                            + ", this = " + this);
                }
                return FINISH_HANDLED;
            }

            if (shouldDropInputEvent(q)) {
                return FINISH_NOT_HANDLED;
            }

            // This dispatch is for windows that don't have a Window.Callback. Otherwise,
            // the Window.Callback usually will have already called this (see
            // DecorView.superDispatchKeyEvent) leaving this call a no-op.
            if (mUnhandledKeyManager.dispatch(mView, event)) {
                return FINISH_HANDLED;
            }

            int groupNavigationDirection = 0;

            if (event.getAction() == KeyEvent.ACTION_DOWN
                    && event.getKeyCode() == KeyEvent.KEYCODE_TAB) {
                if (KeyEvent.metaStateHasModifiers(event.getMetaState(), KeyEvent.META_META_ON)) {
                    groupNavigationDirection = View.FOCUS_FORWARD;
                } else if (KeyEvent.metaStateHasModifiers(event.getMetaState(),
                        KeyEvent.META_META_ON | KeyEvent.META_SHIFT_ON)) {
                    groupNavigationDirection = View.FOCUS_BACKWARD;
                }
            }

            // If a modifier is held, try to interpret the key as a shortcut.
            if (event.getAction() == KeyEvent.ACTION_DOWN
                    && !KeyEvent.metaStateHasNoModifiers(event.getMetaState())
                    && event.getRepeatCount() == 0
                    && !KeyEvent.isModifierKey(event.getKeyCode())
                    && groupNavigationDirection == 0) {
                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) {
                if (groupNavigationDirection != 0) {
                    if (performKeyboardGroupNavigation(groupNavigationDirection)) {
                        return FINISH_HANDLED;
                    }
                } else {
                    if (performFocusNavigation(event)) {
                        return FINISH_HANDLED;
                    }
                }
            }
            return FORWARD;
        }

        private int processPointerEvent(QueuedInputEvent q) {
            final MotionEvent event = (MotionEvent)q.mEvent;

            mAttachInfo.mUnbufferedDispatchRequested = false;
            mAttachInfo.mHandlingPointerEvent = true;
            boolean handled = mView.dispatchPointerEvent(event);
            if (handled && ViewDebugManager.DEBUG_ENG) {
                Log.v(mTag, "App handle pointer event: event = " + event
                             + ", mView = " + mView
                             + ", this = " + this);
            }
            maybeUpdatePointerIcon(event);
            maybeUpdateTooltip(event);
            mAttachInfo.mHandlingPointerEvent = false;
            if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {
                mUnbufferedInputDispatch = true;
                if (mConsumeBatchedInputScheduled) {
                    scheduleConsumeBatchedInputImmediately();
                }
            }
            return handled ? FINISH_HANDLED : FORWARD;
        }

        private void maybeUpdatePointerIcon(MotionEvent event) {
            if (event.getPointerCount() == 1 && event.isFromSource(InputDevice.SOURCE_MOUSE)) {
                if (event.getActionMasked() == MotionEvent.ACTION_HOVER_ENTER
                        || event.getActionMasked() == MotionEvent.ACTION_HOVER_EXIT) {
                    // Other apps or the window manager may change the icon type outside of
                    // this app, therefore the icon type has to be reset on enter/exit event.
                    mPointerIconType = PointerIcon.TYPE_NOT_SPECIFIED;
                }

                if (event.getActionMasked() != MotionEvent.ACTION_HOVER_EXIT) {
                    if (!updatePointerIcon(event) &&
                            event.getActionMasked() == MotionEvent.ACTION_HOVER_MOVE) {
                        mPointerIconType = PointerIcon.TYPE_NOT_SPECIFIED;
                    }
                }
            }
        }

        private int processTrackballEvent(QueuedInputEvent q) {
            final MotionEvent event = (MotionEvent)q.mEvent;

            if (event.isFromSource(InputDevice.SOURCE_MOUSE_RELATIVE)) {
                if (!hasPointerCapture() || mView.dispatchCapturedPointerEvent(event)) {
                    return FINISH_HANDLED;
                }
            }

            if (mView.dispatchTrackballEvent(event)) {
                return FINISH_HANDLED;
            }
            return FORWARD;
        }

        private int processGenericMotionEvent(QueuedInputEvent q) {
            final MotionEvent event = (MotionEvent)q.mEvent;

            if (event.isFromSource(InputDevice.SOURCE_TOUCHPAD)) {
                if (hasPointerCapture() && mView.dispatchCapturedPointerEvent(event)) {
                    return FINISH_HANDLED;
                }
            }

            // Deliver the event to the view.
            if (mView.dispatchGenericMotionEvent(event)) {
                return FINISH_HANDLED;
            }
            return FORWARD;
        }
    }

    private void resetPointerIcon(MotionEvent event) {
        mPointerIconType = PointerIcon.TYPE_NOT_SPECIFIED;
        updatePointerIcon(event);
    }

    private boolean updatePointerIcon(MotionEvent event) {
        final int pointerIndex = 0;
        final float x = event.getX(pointerIndex);
        final float y = event.getY(pointerIndex);
        if (mView == null) {
            // E.g. click outside a popup to dismiss it
            Slog.d(mTag, "updatePointerIcon called after view was removed");
            return false;
        }
        if (x < 0 || x >= mView.getWidth() || y < 0 || y >= mView.getHeight()) {
            // E.g. when moving window divider with mouse
            Slog.d(mTag, "updatePointerIcon called with position out of bounds");
            return false;
        }
        final PointerIcon pointerIcon = mView.onResolvePointerIcon(event, pointerIndex);
        final int pointerType = (pointerIcon != null) ?
                pointerIcon.getType() : PointerIcon.TYPE_DEFAULT;

        if (mPointerIconType != pointerType) {
            mPointerIconType = pointerType;
            mCustomPointerIcon = null;
            if (mPointerIconType != PointerIcon.TYPE_CUSTOM) {
                InputManager.getInstance().setPointerIconType(pointerType);
                return true;
            }
        }
        if (mPointerIconType == PointerIcon.TYPE_CUSTOM &&
                !pointerIcon.equals(mCustomPointerIcon)) {
            mCustomPointerIcon = pointerIcon;
            InputManager.getInstance().setCustomPointerIcon(mCustomPointerIcon);
        }
        return true;
    }

    private void maybeUpdateTooltip(MotionEvent event) {
        if (event.getPointerCount() != 1) {
            return;
        }
        final int action = event.getActionMasked();
        if (action != MotionEvent.ACTION_HOVER_ENTER
                && action != MotionEvent.ACTION_HOVER_MOVE
                && action != MotionEvent.ACTION_HOVER_EXIT) {
            return;
        }
        AccessibilityManager manager = AccessibilityManager.getInstance(mContext);
        if (manager.isEnabled() && manager.isTouchExplorationEnabled()) {
            return;
        }
        if (mView == null) {
            Slog.d(mTag, "maybeUpdateTooltip called after view was removed");
            return;
        }
        mView.dispatchTooltipHoverEvent(event);
    }

    /**
     * Performs synthesis of new input events from unhandled input events.
     */
    final class SyntheticInputStage extends InputStage {
        private final SyntheticTrackballHandler mTrackball = new SyntheticTrackballHandler();
        private final SyntheticJoystickHandler mJoystick = new SyntheticJoystickHandler();
        private final SyntheticTouchNavigationHandler mTouchNavigation =
                new SyntheticTouchNavigationHandler();
        private final SyntheticKeyboardHandler mKeyboard = new SyntheticKeyboardHandler();

        public SyntheticInputStage() {
            super(null);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            q.mFlags |= QueuedInputEvent.FLAG_RESYNTHESIZED;
            if (q.mEvent instanceof MotionEvent) {
                final MotionEvent event = (MotionEvent)q.mEvent;
                final int source = event.getSource();
                if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
                    mTrackball.process(event);
                    return FINISH_HANDLED;
                } else if ((source & InputDevice.SOURCE_CLASS_JOYSTICK) != 0) {
                    mJoystick.process(event);
                    return FINISH_HANDLED;
                } else if ((source & InputDevice.SOURCE_TOUCH_NAVIGATION)
                        == InputDevice.SOURCE_TOUCH_NAVIGATION) {
                    mTouchNavigation.process(event);
                    return FINISH_HANDLED;
                }
            } else if ((q.mFlags & QueuedInputEvent.FLAG_UNHANDLED) != 0) {
                mKeyboard.process((KeyEvent)q.mEvent);
                return FINISH_HANDLED;
            }

            return FORWARD;
        }

        @Override
        protected void onDeliverToNext(QueuedInputEvent q) {
            if ((q.mFlags & QueuedInputEvent.FLAG_RESYNTHESIZED) == 0) {
                // Cancel related synthetic events if any prior stage has handled the event.
                if (q.mEvent instanceof MotionEvent) {
                    final MotionEvent event = (MotionEvent)q.mEvent;
                    final int source = event.getSource();
                    if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
                        mTrackball.cancel();
                    } else if ((source & InputDevice.SOURCE_CLASS_JOYSTICK) != 0) {
                        mJoystick.cancel();
                    } else if ((source & InputDevice.SOURCE_TOUCH_NAVIGATION)
                            == InputDevice.SOURCE_TOUCH_NAVIGATION) {
                        mTouchNavigation.cancel(event);
                    }
                }
            }
            super.onDeliverToNext(q);
        }

        @Override
        protected void onWindowFocusChanged(boolean hasWindowFocus) {
            if (!hasWindowFocus) {
                mJoystick.cancel();
            }
        }

        @Override
        protected void onDetachedFromWindow() {
            mJoystick.cancel();
        }
    }

ViewRootImpl继续分发到DecorView

 一部分事件会在各色InputStage的责任链中消费掉，如果在这些责任链中没有消费掉的事件会继续向上传递给DecorView，向DecorView传递的主要责任链是ViewPostImeInputStage。在ViewRootImpl中的mView就是DecorView，只要看到mView.dispatch这些关键字的代码基本上可以认为是在分发各种事件到DecorView，在ViewPostImeInputStage里分发的主要事件如下：

• mView.dispatchPointerEvent(event);  分发触控事件，在processPointerEvent方法里
• mView.dispatchKeyEvent(event)  分发按键事件，在processKeyEvent方法里
• mView.dispatchKeyShortcutEvent(event) 分发快捷键事件 ，在processKeyEvent方法里
• mView.dispatchCapturedPointerEvent(event)  分发轨迹球指针捕获事件(特别老式的轨迹球设备)，在processTrackballEvent方法里
• mView.dispatchTrackballEvent(event)　分发轨迹球事件，在processTrackballEvent方法里
• mView.dispatchCapturedPointerEvent(event)  分发鼠标指针捕获事件，在processGenericMotionEvent方法里
• mView.dispatchGenericMotionEvent(event)  分发鼠标事件，在processGenericMotionEvent方法里

这里是继续向DecorView分发按键事件的代码片段

 

继续分发到View层

如下经过了DecorView -> Activity -> PhoneWindow -> DecorView -> ViewGroup -> View.

另外插一句，可以举一反三其实触控事件分发也是这个顺序。

第一步，DecorView中的按键分发：

@Override
public boolean dispatchKeyEvent(KeyEvent event) {
    final int keyCode = event.getKeyCode();
    final int action = event.getAction();
    final boolean isDown = action == KeyEvent.ACTION_DOWN;

    if (isDown && (event.getRepeatCount() == 0)) {
        // First handle chording of panel key: if a panel key is held
        // but not released, try to execute a shortcut in it.
        if ((mWindow.mPanelChordingKey > 0) && (mWindow.mPanelChordingKey != keyCode)) {
            boolean handled = dispatchKeyShortcutEvent(event);
            if (handled) {
                return true;
            }
        }

        // If a panel is open, perform a shortcut on it without the
        // chorded panel key
        if ((mWindow.mPreparedPanel != null) && mWindow.mPreparedPanel.isOpen) {
            if (mWindow.performPanelShortcut(mWindow.mPreparedPanel, keyCode, event, 0)) {
                return true;
            }
        }
    }

    if (!mWindow.isDestroyed()) {
        //cb其实就是对应的Activity/Dialog，这里分发给了Activity
        final Window.Callback cb = mWindow.getCallback();
        final boolean handled = cb != null && mFeatureId < 0 ? cb.dispatchKeyEvent(event)
                : super.dispatchKeyEvent(event);
        if (handled) {
            return true;
        }
    }

    return isDown ? mWindow.onKeyDown(mFeatureId, event.getKeyCode(), event)
            : mWindow.onKeyUp(mFeatureId, event.getKeyCode(), event);
}

第二步，Activity的按键分发

    /**
     * Called to process key events.  You can override this to intercept all
     * key events before they are dispatched to the window.  Be sure to call
     * this implementation for key events that should be handled normally.
     *
     * @param event The key event.
     *
     * @return boolean Return true if this event was consumed.
     */
    public boolean dispatchKeyEvent(KeyEvent event) {
        onUserInteraction();

        // Let action bars open menus in response to the menu key prioritized over
        // the window handling it
        final int keyCode = event.getKeyCode();
        if (keyCode == KeyEvent.KEYCODE_MENU &&
                mActionBar != null && mActionBar.onMenuKeyEvent(event)) {
            return true;
        }

        Window win = getWindow();
        if (win.superDispatchKeyEvent(event)) { //这里分发给了PhoneWindow
            return true;
        }
        View decor = mDecor;
        if (decor == null) decor = win.getDecorView();
        return event.dispatch(this, decor != null
                ? decor.getKeyDispatcherState() : null, this);
    }

第三步，PhoneWindow的按键分发

    @Override
    public boolean superDispatchKeyEvent(KeyEvent event) {
        return mDecor.superDispatchKeyEvent(event); //这里继续分发给了DecorView
    }

第四步，DecorView的按键再分发，这里回头分发给DecorView，是为了DecorView与Activity的解耦，因为Activity只持有Window。 另外你可以看到上面Window的分发代码就是转个手而已

    public boolean superDispatchKeyEvent(KeyEvent event) {
        // Give priority to closing action modes if applicable.
        if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) { //如果是back键这里会直接消费掉
            final int action = event.getAction();
            // Back cancels action modes first.
            if (mPrimaryActionMode != null) {
                if (action == KeyEvent.ACTION_UP) {
                    mPrimaryActionMode.finish();
                }
                return true;
            }
        }

        if (super.dispatchKeyEvent(event)) {  //这里继续分发给ViewGroup
            return true;
        }

        return (getViewRootImpl() != null) && getViewRootImpl().dispatchUnhandledKeyEvent(event);
    }

第五步，ViewGroup的按键分发

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onKeyEvent(event, 1);
        }

        if ((mPrivateFlags & (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS))
                == (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS)) {
            if (super.dispatchKeyEvent(event)) { //这里会继续分发给View
                return true;
            }
        } else if (mFocused != null && (mFocused.mPrivateFlags & PFLAG_HAS_BOUNDS)
                == PFLAG_HAS_BOUNDS) {
            if (mFocused.dispatchKeyEvent(event)) { //这个是分发ViewGroup给有焦点的子View
                return true;
            }
        }

        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(event, 1);
        }
        return false;
    }

第六步，View的按键分发，到终点了

    public boolean dispatchKeyEvent(KeyEvent event) {
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onKeyEvent(event, 0);
        }

        // Give any attached key listener a first crack at the event.
        //noinspection SimplifiableIfStatement
        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnKeyListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
                && li.mOnKeyListener.onKey(this, event.getKeyCode(), event)) { //这里已经回调到mOnKeyListener了，我们应用层就可以接收到按键键值了
            return true;
        }

        if (event.dispatch(this, mAttachInfo != null
                ? mAttachInfo.mKeyDispatchState : null, this)) {
            return true;
        }

        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
        }
        return false;
    }

 

 

 

End