Input系统学习----AccessibilityService 的dispatchGesture注入点击方法的调用流程（InputFilter）

AccessibilityService 的dispatchGesture方法可以注入触控事件来进行模拟操作，

Github上有个不错的例子，通过识别面部移动来注入点击事件，https://github.com/cmauri/eva_facial_mouse

dispatchGesture的处理流程是怎样的呢，这里粗略查看一下，


664    public final boolean dispatchGesture(@NonNull GestureDescription gesture,

665            @Nullable GestureResultCallback callback,

666            @Nullable Handler handler) {



686                connection.sendGesture(mGestureStatusCallbackSequence,
687                        new ParceledListSlice<>(steps));

frameworks/base/services/accessibility/java/com/android/server/accessibility/AccessibilityServiceConnection.java


353    public void sendGesture(int sequence, ParceledListSlice gestureSteps) {
354        synchronized (mLock) {
355            if (mSecurityPolicy.canPerformGestures(this)) {
356                MotionEventInjector motionEventInjector =
357                        mSystemSupport.getMotionEventInjectorLocked();
358                if (motionEventInjector != null) {
359                    motionEventInjector.injectEvents(
360                            gestureSteps.getList(), mServiceInterface, sequence);
361                } else {
362                    try {
363                        mServiceInterface.onPerformGestureResult(sequence, false);
364                    } catch (RemoteException re) {
365                        Slog.e(LOG_TAG, "Error sending motion event injection failure to "
366                                + mServiceInterface, re);
367                    }
368                }

frameworks/base/services/accessibility/java/com/android/server/accessibility/MotionEventInjector.java

这个注释值得注意，injectEvents调用会cancel之前的手势

94    /**
95     * Schedule a gesture for injection. The gesture is defined by a set of {@code GestureStep}s,
96     * from which {@code MotionEvent}s will be derived. All gestures currently in progress will be
97     * cancelled.
98     *
99     * @param gestureSteps The gesture steps to inject.
100     * @param serviceInterface The interface to call back with a result when the gesture is
101     * either complete or cancelled.
102     */


103    public void injectEvents(List<GestureStep> gestureSteps,
104            IAccessibilityServiceClient serviceInterface, int sequence) {
105        SomeArgs args = SomeArgs.obtain();
106        args.arg1 = gestureSteps;
107        args.arg2 = serviceInterface;
108        args.argi1 = sequence;
109        mHandler.sendMessage(mHandler.obtainMessage(MESSAGE_INJECT_EVENTS, args));
110    }

调用到

136    public boolean handleMessage(Message message) {
137        if (message.what == MESSAGE_INJECT_EVENTS) {
138            SomeArgs args = (SomeArgs) message.obj;
139            injectEventsMainThread((List<GestureStep>) args.arg1,
140                    (IAccessibilityServiceClient) args.arg2, args.argi1);
141            args.recycle();
142            return true;
143        }




158    private void injectEventsMainThread(List<GestureStep> gestureSteps,
159            IAccessibilityServiceClient serviceInterface, int sequence) {


201        for (int i = 0; i < events.size(); i++) {
202            MotionEvent event = events.get(i);
203            int isEndOfSequence = (i == events.size() - 1) ? 1 : 0;
204            Message message = mHandler.obtainMessage(
205                    MESSAGE_SEND_MOTION_EVENT, isEndOfSequence, 0, event);
206            mLastScheduledEventTime = event.getEventTime();
207            mHandler.sendMessageDelayed(message, Math.max(0, event.getEventTime() - currentTime));
208        }

查看MESSAGE_SEND_MOTION_EVENT

的处理

136    public boolean handleMessage(Message message) {

137        if (message.what == MESSAGE_INJECT_EVENTS) {

138            SomeArgs args = (SomeArgs) message.obj;

139            injectEventsMainThread((List<GestureStep>) args.arg1,

140                    (IAccessibilityServiceClient) args.arg2, args.argi1);

141            args.recycle();

142            return true;

143        }

144        if (message.what != MESSAGE_SEND_MOTION_EVENT) {

145            Slog.e(LOG_TAG, "Unknown message: " + message.what);

146            return false;

147        }

148        MotionEvent motionEvent = (MotionEvent) message.obj;

149        sendMotionEventToNext(motionEvent, motionEvent, WindowManagerPolicy.FLAG_PASS_TO_USER);

150        boolean isEndOfSequence = message.arg1 != 0;

151        if (isEndOfSequence) {

152            notifyService(mServiceInterfaceForCurrentGesture, mSequencesInProgress.get(0), true);

153            mSequencesInProgress.remove(0);

154        }

155        return true;

156    }

280    private void sendMotionEventToNext(MotionEvent event, MotionEvent rawEvent,

281            int policyFlags) {

282        if (getNext() != null) {

283            super.onMotionEvent(event, rawEvent, policyFlags);

284            if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {

285                mOpenGesturesInProgress.put(event.getSource(), true);

286            }

287            if ((event.getActionMasked() == MotionEvent.ACTION_UP)

288                    || (event.getActionMasked() == MotionEvent.ACTION_CANCEL)) {

289                mOpenGesturesInProgress.put(event.getSource(), false);

290            }

291        }

292    }

这里的super.onMotionEvent 调用到AccessibilityInputFilter.java的

onMotionEvent方法，

353    public void onMotionEvent(MotionEvent transformedEvent, MotionEvent rawEvent,

354            int policyFlags) {

355        sendInputEvent(transformedEvent, policyFlags);

356    }

因为AccessibilityInputFilter extends InputFilter，所以其sendInputEvent方法实现了事件的注入。

class AccessibilityInputFilter extends InputFilter implements EventStreamTransformation {

MotionEventInjector的super.onMotionEvent方法为什么调到AccessibilityInputFilter.java的onMotionEvent方法里了呢？

这个过程比较晦涩，super.onMotionEvent方法调用其父类BaseEventStreamTransformation的同名方法，

public class MotionEventInjector extends BaseEventStreamTransformation implements Handler.Callback {

BaseEventStreamTransformation是个抽象类，实现的接口EventStreamTransformation类里有onMotionEvent方法的定义，

19abstract class BaseEventStreamTransformation implements EventStreamTransformation {

20    private EventStreamTransformation mNext;

22    @Override

23    public void setNext(EventStreamTransformation next) {

24        mNext = next;

25    }

27    @Override

28    public EventStreamTransformation getNext() {

29        return mNext;

30    }

31}

frameworks/base/services/accessibility/java/com/android/server/accessibility/EventStreamTransformation.java

68    default void onMotionEvent(MotionEvent event, MotionEvent rawEvent, int policyFlags) {
69        EventStreamTransformation next = getNext();
70        if (next != null) {
71            next.onMotionEvent(event, rawEvent, policyFlags);
72        }
73    }

调用next.onMotionEvent方法，

next是什么呢，回到motionEventInjector定义的地方，

frameworks/base/services/accessibility/java/com/android/server/accessibility/AccessibilityServiceConnection.java


353    public void sendGesture(int sequence, ParceledListSlice gestureSteps) {
354        synchronized (mLock) {
355            if (mSecurityPolicy.canPerformGestures(this)) {
356                MotionEventInjector motionEventInjector =
357                        mSystemSupport.getMotionEventInjectorLocked();

其赋值来自

mSystemSupport.getMotionEventInjectorLocked()

AccessibilityManagerService.java

951    public MotionEventInjector getMotionEventInjectorLocked() {
952        final long endMillis = SystemClock.uptimeMillis() + WAIT_MOTION_INJECTOR_TIMEOUT_MILLIS;
953        while ((mMotionEventInjector == null) && (SystemClock.uptimeMillis() < endMillis)) {
954            try {
955                mLock.wait(endMillis - SystemClock.uptimeMillis());
956            } catch (InterruptedException ie) {
957                /* ignore */
958            }
959        }
960        if (mMotionEventInjector == null) {
961            Slog.e(LOG_TAG, "MotionEventInjector installation timed out");
962        }
963        return mMotionEventInjector;
964    }

这个mMotionEventInjector是在哪里new的呢，在AccessibilityManagerService.java里只有一个赋值的地方，

在AccessibilityManagerService.java里

936    /**
937     * Called by AccessibilityInputFilter when it creates or destroys the motionEventInjector.
938     * Not using a getter because the AccessibilityInputFilter isn't thread-safe
939     *
940     * @param motionEventInjector The new value of the motionEventInjector. May be null.
941     */
942    void setMotionEventInjector(MotionEventInjector motionEventInjector) {
943        synchronized (mLock) {
944            mMotionEventInjector = motionEventInjector;
945            // We may be waiting on this object being set
946            mLock.notifyAll();
947        }
948    }

从注释可以看到，这个方法是在AccessibilityInputFilter里调用的

class AccessibilityInputFilter extends InputFilter implements EventStreamTransformation {

在AccessibilityInputFilter.java的enableFeatures()方法中，有对mMotionEventInjector的关联操作，


415    private void enableFeatures() {


443        if ((mEnabledFeatures & FLAG_FEATURE_INJECT_MOTION_EVENTS) != 0) {
444            mMotionEventInjector = new MotionEventInjector(mContext.getMainLooper());
445            addFirstEventHandler(mMotionEventInjector);
446            mAms.setMotionEventInjector(mMotionEventInjector);
447        }

addFirstEventHandler(mMotionEventInjector);

里面

462    private void addFirstEventHandler(EventStreamTransformation handler) {

463        if (mEventHandler != null) {

464            handler.setNext(mEventHandler);

465        } else {

466            handler.setNext(this);

467        }

468        mEventHandler = handler;

469    }

把this传给mMotionEventInjector的setNext方法。

所以前面MotionEventInjector的super.onMotionEvent方法调用到这里，实现了事件的注入

353    public void onMotionEvent(MotionEvent transformedEvent, MotionEvent rawEvent,
354            int policyFlags) {
355        sendInputEvent(transformedEvent, policyFlags);
356    }

关于sendInputEvent的注入，可以参考

https://zhuanlan.zhihu.com/p/31195334

可以看到，从AccessibilityService到AccessibilityManagerService.java，以及里面使用的AccessibilityInputFilter，在这个流程中串起来了。

Input系统学习----AccessibilityService 的dispatchGesture注入点击方法的调用流程（InputFilter）

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