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Android 无障碍服务 performAction 调用过程分析_Android

作者：自动化BUG制造器更新时间： 2022-08-07 编程语言

ACTION_FOCUS // 获取焦点
ACTION_CLEAR_FOCUS // 清除焦点
ACTION_SELECT // 选中
ACTION_CLEAR_SELECTION // 清除选中状态
ACTION_ACCESSIBILITY_FOCUS // 无障碍焦点
ACTION_CLEAR_ACCESSIBILITY_FOCUS // 清除无障碍焦点
ACTION_CLICK // 点击
ACTION_LONG_CLICK // 长按
ACTION_NEXT_AT_MOVEMENT_GRANULARITY // 下一步移动
ACTION_PREVIOUS_AT_MOVEMENT_GRANULARITY // 上一步移动
ACTION_NEXT_HTML_ELEMENT // 下一个 html 元素
ACTION_PREVIOUS_HTML_ELEMENT // 上一个 html 元素
ACTION_SCROLL_FORWARD // 向前滑动
ACTION_SCROLL_BACKWARD // 向后滑动

他们都可以通过performAction方法进行处理：

// in AccessibilityNodeInfo
public boolean performAction(int action) {
    enforceSealed();
    if (!canPerformRequestOverConnection(mConnectionId, mWindowId, mSourceNodeId)) {
        return false;
    }
    AccessibilityInteractionClient client = AccessibilityInteractionClient.getInstance();
    return client.performAccessibilityAction(mConnectionId, mWindowId, mSourceNodeId,
            action, null);
}

在这个方法中，第一步是检查 perform 是否可以通过 connection 请求，这里 connection 检查是根据通过 binder 通信传递过来的 id 检查连接是否正常。然后通过AccessibilityInteractionClient对象，调用它的performAccessibilityAction方法去进行实际操作的。

AccessibilityInteractionClient

这个类是一个执行可访问性交互的单例，它可以根据 View 的快照查询远程的 View 层次结构，以及通过 View 层次结构，来请求对 View 执行某项操作。

基本原理：内容检索 API 从客户端的角度来看是同步的，但在内部它们是异步的。客户端线程调用系统请求操作并提供回调以接收结果，然后等待该结果的超时。系统强制执行安全性并将请求委托给给定的视图层次结构，在该视图层次结构中发布消息（来自 Binder 线程），描述 UI 线程要执行的内容，其结果是通过上述回调传递的。但是，被阻塞的客户端线程和目标视图层次结构的主 UI 线程可以是同一个线程，例如无障碍服务和 Activity 在同一个进程中运行，因此它们在同一个主线程上执行。在这种情况下，检索将会失败，因为 UI 线程在等待检索结果，会导致阻塞。为了避免在进行调用时出现这种情况，客户端还会传递其进程和线程 ID，以便访问的视图层次结构可以检测发出请求的客户端是否正在其主 UI 线程中运行。在这种情况下，视图层次结构，特别是对它执行 IPC 的绑定线程，不会发布要在 UI 线程上运行的消息，而是将其传递给单例交互客户端，通过该客户端发生所有交互，后者负责执行开始等待通过回调传递的异步结果之前的消息。在这种情况下，已经收到预期的结果，因此不执行等待。

上面是官方备注的描述，大概意思最好不要在主线程执行检索操作。

继续跟进它的performAccessibilityAction方法：

    public boolean performAccessibilityAction(int connectionId, int accessibilityWindowId,
            long accessibilityNodeId, int action, Bundle arguments) {
        try {
            IAccessibilityServiceConnection connection = getConnection(connectionId);
            if (connection != null) {
                final int interactionId = mInteractionIdCounter.getAndIncrement();
                final long identityToken = Binder.clearCallingIdentity();
                final boolean success;
                try {
                    success = connection.performAccessibilityAction(
                            accessibilityWindowId, accessibilityNodeId, action, arguments,
                            interactionId, this, Thread.currentThread().getId()); // 【*】
                } finally {
                    Binder.restoreCallingIdentity(identityToken);
                }
                if (success) {
                    return getPerformAccessibilityActionResultAndClear(interactionId);
                }
            }
        } catch (RemoteException re) {
            Log.w(LOG_TAG, "Error while calling remote performAccessibilityAction", re);
        }
        return false;
    }

这里通过 getConnection(connectionId) 获取了一个 IAccessibilityServiceConnection 。

public static IAccessibilityServiceConnection getConnection(int connectionId) {
    synchronized (sConnectionCache) {
        return sConnectionCache.get(connectionId);
    }
}

这里的 sConnectionCache 通过 AccessibilityInteractionClient 的addConnection添加数据的，addConnection在 AccessbilityService 创建初始化时调用的：

case DO_INIT: {
    mConnectionId = message.arg1;
    SomeArgs args = (SomeArgs) message.obj;
    IAccessibilityServiceConnection connection = (IAccessibilityServiceConnection) args.arg1;
    IBinder windowToken = (IBinder) args.arg2;
    args.recycle();
    if (connection != null) {
        AccessibilityInteractionClient.getInstance(mContext).addConnection(mConnectionId, connection);
        mCallback.init(mConnectionId, windowToken);
        mCallback.onServiceConnected();
    } else {
        AccessibilityInteractionClient.getInstance(mContext).removeConnection(mConnectionId);
        mConnectionId = AccessibilityInteractionClient.NO_ID;
        AccessibilityInteractionClient.getInstance(mContext).clearCache();
        mCallback.init(AccessibilityInteractionClient.NO_ID, null);
    }
    return;
}

也就是说，在 AccessbilityService 创建时，会将一个表示连接的对象存到 AccessibilityInteractionClient 的连接缓存中。

IAccessibilityServiceConnection

它是 AccessibilityManagerService 向 AccessbilityService 暴露的 AIDL 接口，提供给 AccessbilityService 调用AccessibilityManagerService 的能力。上面的 performAction 流程中，调用到了 connection 的performAccessibilityAction方法。而 IAccessibilityServiceConnection 有两个实现类，AccessibilityServiceConnectionImpl和AbstractAccessibilityServiceConnection，前者都是空实现，显然不是我们要调用到的地方，后者的performAccessibilityAction：

@Override
public boolean performAccessibilityAction(int accessibilityWindowId,
        long accessibilityNodeId, int action, Bundle arguments, int interactionId,
        IAccessibilityInteractionConnectionCallback callback, long interrogatingTid)
        throws RemoteException {
    final int resolvedWindowId;
    synchronized (mLock) {
        if (!hasRightsToCurrentUserLocked()) {
            return false;
        }
        resolvedWindowId = resolveAccessibilityWindowIdLocked(accessibilityWindowId);
        if (!mSecurityPolicy.canGetAccessibilityNodeInfoLocked(
                mSystemSupport.getCurrentUserIdLocked(), this, resolvedWindowId)) {
            return false;
        }
    }
    if (!mSecurityPolicy.checkAccessibilityAccess(this)) {
        return false;
    }
    return performAccessibilityActionInternal(
            mSystemSupport.getCurrentUserIdLocked(), resolvedWindowId, accessibilityNodeId,
            action, arguments, interactionId, callback, mFetchFlags, interrogatingTid);
}

最后的一行调用：

    private boolean performAccessibilityActionInternal(int userId, int resolvedWindowId, long accessibilityNodeId, int action, Bundle arguments, int interactionId, IAccessibilityInteractionConnectionCallback callback, int fetchFlags, long interrogatingTid) {
        RemoteAccessibilityConnection connection;
        IBinder activityToken = null;
        // 同步获取 connection
        synchronized (mLock) {
            connection = mA11yWindowManager.getConnectionLocked(userId, resolvedWindowId);
            if (connection == null)  {
                return false;
            }
            final boolean isA11yFocusAction = (action == ACTION_ACCESSIBILITY_FOCUS) || (action == ACTION_CLEAR_ACCESSIBILITY_FOCUS);
            if (!isA11yFocusAction) {
                final WindowInfo windowInfo = mA11yWindowManager.findWindowInfoByIdLocked(resolvedWindowId);
                if (windowInfo != null) activityToken = windowInfo.activityToken;
            }
            final AccessibilityWindowInfo a11yWindowInfo = mA11yWindowManager.findA11yWindowInfoByIdLocked(resolvedWindowId);
            if (a11yWindowInfo != null && a11yWindowInfo.isInPictureInPictureMode() && mA11yWindowManager.getPictureInPictureActionReplacingConnection() != null && !isA11yFocusAction) {
                connection = mA11yWindowManager.getPictureInPictureActionReplacingConnection();
            }
        }
        // 通过 connection 调用到远程服务的performAccessibilityAction
        final int interrogatingPid = Binder.getCallingPid();
        final long identityToken = Binder.clearCallingIdentity();
        try {
            // 无论操作是否成功，它都是由用户操作的无障碍服务生成的，因此请注意用户Activity。
            mPowerManager.userActivity(SystemClock.uptimeMillis(), PowerManager.USER_ACTIVITY_EVENT_ACCESSIBILITY, 0);

            if (action == ACTION_CLICK || action == ACTION_LONG_CLICK) {
                mA11yWindowManager.notifyOutsideTouch(userId, resolvedWindowId);
            }
            if (activityToken != null) {
                LocalServices.getService(ActivityTaskManagerInternal.class).setFocusedActivity(activityToken);
            }
            connection.getRemote().performAccessibilityAction(accessibilityNodeId, action, arguments, interactionId, callback, fetchFlags, interrogatingPid, interrogatingTid);
        } catch (RemoteException re) {
            if (DEBUG) {
                Slog.e(LOG_TAG, "Error calling performAccessibilityAction: " + re);
            }
            return false;
        } finally {
            Binder.restoreCallingIdentity(identityToken);
        }
        return true;
    }

在这个方法中，通过 connection 调用到了远端的 performAccessibilityAction 方法。

关键的一行是：

connection.getRemote().performAccessibilityAction(accessibilityNodeId, action, arguments, interactionId, callback, fetchFlags, interrogatingPid, interrogatingTid);

这里的 connection 类型定义成了RemoteAccessibilityConnection。

RemoteAccessibilityConnection

RemoteAccessibilityConnection 是AccessibilityWindowManager的内部类，它的getRemote()返回类型是IAccessibilityInteractionConnection。

AccessibilityWindowManager

此类为 AccessibilityManagerService 提供 API 来管理 AccessibilityWindowInfo 和 WindowInfos。

IAccessibilityInteractionConnection

这是一个 AIDL 中定义的接口，用来进行给定 window 中 AccessibilityManagerService 和 ViewRoot 之间交互的接口。

也就是说getRemote(). performAccessibilityAction(...)最终来到了 ViewRootImpl 中。

AccessibilityInteractionConnection

ViewRootImpl 中存在一个内部类AccessibilityInteractionConnection，它是这个 ViewAncestor 提供给 AccessibilityManagerService 的一个接口，后者可以与这个 ViewAncestor 中的视图层次结构进行交互。

它的performAccessibilityAction实现是：

@Override
public void performAccessibilityAction(long accessibilityNodeId, int action, Bundle arguments, int interactionId, IAccessibilityInteractionConnectionCallback callback, int flags, int interrogatingPid, long interrogatingTid) {
    ViewRootImpl viewRootImpl = mViewRootImpl.get();
    if (viewRootImpl != null && viewRootImpl.mView != null) {
        viewRootImpl.getAccessibilityInteractionController().performAccessibilityActionClientThread(accessibilityNodeId, action, arguments,
                    interactionId, callback, flags, interrogatingPid, interrogatingTid);
    } else {
        // We cannot make the call and notify the caller so it does not wait.
        try {
            callback.setPerformAccessibilityActionResult(false, interactionId);
        } catch (RemoteException re) {
            /* best effort - ignore */
        }
    }
}

内部又是通过代理调用，ViewRootImpl 的 getAccessibilityInteractionController() 返回了一个 AccessibilityInteractionController 对象。

AccessibilityInteractionController

它的 performAccessibilityActionClientThread :

public void performAccessibilityActionClientThread(long accessibilityNodeId, int action,
        Bundle arguments, int interactionId,
        IAccessibilityInteractionConnectionCallback callback, int flags, int interrogatingPid,
        long interrogatingTid) {
    Message message = mHandler.obtainMessage();
    message.what = PrivateHandler.MSG_PERFORM_ACCESSIBILITY_ACTION;
    message.arg1 = flags;
    message.arg2 = AccessibilityNodeInfo.getAccessibilityViewId(accessibilityNodeId);
    SomeArgs args = SomeArgs.obtain();
    args.argi1 = AccessibilityNodeInfo.getVirtualDescendantId(accessibilityNodeId);
    args.argi2 = action;
    args.argi3 = interactionId;
    args.arg1 = callback;
    args.arg2 = arguments;
    message.obj = args;
    scheduleMessage(message, interrogatingPid, interrogatingTid, CONSIDER_REQUEST_PREPARERS);
}

组装了一个 message ，并通过 scheduleMessage 方法去执行：

private void scheduleMessage(Message message, int interrogatingPid, long interrogatingTid, boolean ignoreRequestPreparers) {
    if (ignoreRequestPreparers || !holdOffMessageIfNeeded(message, interrogatingPid, interrogatingTid)) {
        if (interrogatingPid == mMyProcessId && interrogatingTid == mMyLooperThreadId
                && mHandler.hasAccessibilityCallback(message)) {
            AccessibilityInteractionClient.getInstanceForThread(
                    interrogatingTid).setSameThreadMessage(message);
        } else {

            if (!mHandler.hasAccessibilityCallback(message) && Thread.currentThread().getId() == mMyLooperThreadId) {
                mHandler.handleMessage(message);
            } else {
                mHandler.sendMessage(message);
            }
        }
    }
}

这里实际上，如果是在主线程，则处理消息，如果不是，则发送消息到主线程处理。handler 的类型是 PrivateHandler ，在 AccessibilityInteractionController 内部定义。

它的处理消息方法的实现是：

@Override
public void handleMessage(Message message) {
    final int type = message.what;
    switch (type) {
        // ...
        case MSG_PERFORM_ACCESSIBILITY_ACTION: {
            performAccessibilityActionUiThread(message);
        } break;
        // ...
        default:
            throw new IllegalArgumentException("Unknown message type: " + type);
    }
}

执行到了 performAccessibilityActionUiThread(message); :

    private void performAccessibilityActionUiThread(Message message) {
        // ... 
        boolean succeeded = false;
        try {
            // ...
            final View target = findViewByAccessibilityId(accessibilityViewId);
            if (target != null && isShown(target)) {
                mA11yManager.notifyPerformingAction(action);
                if (action == R.id.accessibilityActionClickOnClickableSpan) {
                    // 单独处理这个 hidden action
                    succeeded = handleClickableSpanActionUiThread(target, virtualDescendantId, arguments);
                } else {
                    AccessibilityNodeProvider provider = target.getAccessibilityNodeProvider();
                    if (provider != null) {
                        succeeded = provider.performAction(virtualDescendantId, action, arguments);
                    } else if (virtualDescendantId == AccessibilityNodeProvider.HOST_VIEW_ID) {
                        succeeded = target.performAccessibilityAction(action, arguments);
                    }
                }
                mA11yManager.notifyPerformingAction(0);
            }
        } finally {
            try {
                mViewRootImpl.mAttachInfo.mAccessibilityFetchFlags = 0;
                callback.setPerformAccessibilityActionResult(succeeded, interactionId);
            } catch (RemoteException re) {
                /* ignore - the other side will time out */
            }
        }
    }

在这个流程中，分为三种情况去真正执行 performAction ：

1. action == R.id.accessibilityActionClickOnClickableSpan

private boolean handleClickableSpanActionUiThread(
        View view, int virtualDescendantId, Bundle arguments) {
    Parcelable span = arguments.getParcelable(ACTION_ARGUMENT_ACCESSIBLE_CLICKABLE_SPAN);
    if (!(span instanceof AccessibilityClickableSpan)) {
        return false;
    }
    // Find the original ClickableSpan if it's still on the screen
    AccessibilityNodeInfo infoWithSpan = null;
    AccessibilityNodeProvider provider = view.getAccessibilityNodeProvider();
    if (provider != null) {
        infoWithSpan = provider.createAccessibilityNodeInfo(virtualDescendantId);
    } else if (virtualDescendantId == AccessibilityNodeProvider.HOST_VIEW_ID) {
        infoWithSpan = view.createAccessibilityNodeInfo();
    }
    if (infoWithSpan == null) {
        return false;
    }
    // Click on the corresponding span
    ClickableSpan clickableSpan = ((AccessibilityClickableSpan) span).findClickableSpan(
            infoWithSpan.getOriginalText());
    if (clickableSpan != null) {
        clickableSpan.onClick(view);
        return true;
    }
    return false;
}

2. View. AccessibilityNodeProvider != null

当能够通过 View 获取到 AccessibilityNodeProvider 对象是，通过它的 performAction 方法，去执行真正的调用，它的真正调用在 AccessibilityNodeProviderCompat中，这个 Compat 的实现在ExploreByTouchHelper中的内部类MyNodeProvider中：

@Override
public boolean performAction(int virtualViewId, int action, Bundle arguments) {
    return ExploreByTouchHelper.this.performAction(virtualViewId, action, arguments);
}

在 ExploreByTouchHelper 中继续查看：

boolean performAction(int virtualViewId, int action, Bundle arguments) {
    switch (virtualViewId) {
        case HOST_ID:
            return performActionForHost(action, arguments);
        default:
            return performActionForChild(virtualViewId, action, arguments);
    }
}

private boolean performActionForHost(int action, Bundle arguments) {
    return ViewCompat.performAccessibilityAction(mHost, action, arguments);
}
private boolean performActionForChild(int virtualViewId, int action, Bundle arguments) {
    switch (action) {
        case AccessibilityNodeInfoCompat.ACTION_ACCESSIBILITY_FOCUS:
            return requestAccessibilityFocus(virtualViewId);
        case AccessibilityNodeInfoCompat.ACTION_CLEAR_ACCESSIBILITY_FOCUS:
            return clearAccessibilityFocus(virtualViewId);
        case AccessibilityNodeInfoCompat.ACTION_FOCUS:
            return requestKeyboardFocusForVirtualView(virtualViewId);
        case AccessibilityNodeInfoCompat.ACTION_CLEAR_FOCUS:
            return clearKeyboardFocusForVirtualView(virtualViewId);
        default:
            return onPerformActionForVirtualView(virtualViewId, action, arguments);
    }
}

前者调用到了 ViewCompat :

public static boolean performAccessibilityAction(@NonNull View view, int action,
        Bundle arguments) {
    if (Build.VERSION.SDK_INT >= 16) {
        return view.performAccessibilityAction(action, arguments);
    }
    return false;
}

然后是 View 的：

public boolean performAccessibilityAction(int action, Bundle arguments) {
  if (mAccessibilityDelegate != null) {
      return mAccessibilityDelegate.performAccessibilityAction(this, action, arguments);
  } else {
      return performAccessibilityActionInternal(action, arguments);
  }
}

mAccessibilityDelegate.performAccessibilityAction的实现是：

public boolean performAccessibilityAction(View host, int action, Bundle args) {
    return host.performAccessibilityActionInternal(action, args);
}

也是调用到了 View 的performAccessibilityActionInternal 。 performAccessibilityActionInternal 的实现是：

// in View.java
public boolean performAccessibilityActionInternal(int action, Bundle arguments) {
    if (isNestedScrollingEnabled()
            && (action == AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD
            || action == AccessibilityNodeInfo.ACTION_SCROLL_FORWARD
            || action == R.id.accessibilityActionScrollUp
            || action == R.id.accessibilityActionScrollLeft
            || action == R.id.accessibilityActionScrollDown
            || action == R.id.accessibilityActionScrollRight)) {
        if (dispatchNestedPrePerformAccessibilityAction(action, arguments)) {
            return true;
        }
    }

    switch (action) {
        case AccessibilityNodeInfo.ACTION_CLICK: {
            if (isClickable()) {
                performClickInternal();
                return true;
            }
        } break;
        case AccessibilityNodeInfo.ACTION_LONG_CLICK: {
            if (isLongClickable()) {
                performLongClick();
                return true;
            }
        } break;
        // ...
    }
    return false;
}

以 AccessibilityNodeInfo.ACTION_CLICK 为例，内部调用是：

private boolean performClickInternal() {
    // Must notify autofill manager before performing the click actions to avoid scenarios where
    // the app has a click listener that changes the state of views the autofill service might
    // be interested on.
    notifyAutofillManagerOnClick();

    return performClick();
}

这样就调用到了 View 的点击事件。

3. View. AccessibilityNodeProvider == null && virtualDescendantId == AccessibilityNodeProvider.HOST_VIEW_ID

target.performAccessibilityAction(action, arguments);

这里 target 是个 View，也是走的 View 的 performAccessibilityAction ，和上面流程一样。

View 的 performClick 方法是同步的还是异步的？

public boolean performClick() {
    // We still need to call this method to handle the cases where performClick() was called
    // externally, instead of through performClickInternal()
    notifyAutofillManagerOnClick();
    final boolean result;
    final ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnClickListener != null) {
        playSoundEffect(SoundEffectConstants.CLICK);
        li.mOnClickListener.onClick(this);
        result = true;
    } else {
        result = false;
    }
    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
    notifyEnterOrExitForAutoFillIfNeeded(true);
    return result;
}

同步的。

总结

原文链接：https://juejin.cn/post/7088275008971079688

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网站首页编程语言正文

Android 无障碍服务 performAction 调用过程分析_Android

目录

AccessibilityInteractionClient

IAccessibilityServiceConnection

RemoteAccessibilityConnection

AccessibilityWindowManager

IAccessibilityInteractionConnection

AccessibilityInteractionConnection

AccessibilityInteractionController

View 的 performClick 方法是同步的还是异步的？

总结

相关推荐

网站首页 编程语言 正文

Android 无障碍服务 performAction 调用过程分析_Android

目录

AccessibilityInteractionClient

IAccessibilityServiceConnection

RemoteAccessibilityConnection

AccessibilityWindowManager

IAccessibilityInteractionConnection

AccessibilityInteractionConnection

AccessibilityInteractionController

View 的 performClick 方法是同步的还是异步的？

总结

相关推荐

网站首页编程语言正文