一、本文需要解決的問題
之前本人做了一個專案，需要用到AccessibilityService這個系統提供的擴充服務。這個服務本意是作為Android系統的一個輔助功能，去幫助殘疾人更好地使用手機。但是由於它的一些特性，給很多專案的實現提供了一個新的思路，例如之前大名鼎鼎的微信搶紅包外掛，本質上就是使用了這個服務。我研究AccessibilityService的目的是解決以下幾個我在使用過程中所思考的問題：
- AccessibilityService這個Service跟一般的Service有什麼區別？
- AccessibilityService是如何做到監控並捕捉使用者行為的？
- AccessibilityService是如何做到查詢控制元件，執行點選等操作的？
二、初步分析
本文基於Android 7.1的原始碼對AccessibilityService進行分析。 為了更好地理解和分析程式碼，我寫了一個demo，如果想學習具體的使用方法，可以參考Google官方文件AccessibilityService。本文不做AccessibilityService的具體使用教程。
建立AccessibilityService
public class MyAccessibilityService extends AccessibilityService {
private static final String TAG = "MyAccessibilityService";
@Override
public void onCreate() {
super.onCreate();
Log.i(TAG, "onCreate");
}
@Override
public void onAccessibilityEvent(AccessibilityEvent event) {
int eventType = event.getEventType();
switch (eventType) {
case AccessibilityEvent.TYPE_VIEW_CLICKED:
// 捕獲到點選事件
Log.i(TAG, "capture click event!");
AccessibilityNodeInfo nodeInfo = getRootInActiveWindow();
if (nodeInfo != null) {
// 查詢text為Test!的控制元件
List<AccessibilityNodeInfo> button = nodeInfo.findAccessibilityNodeInfosByText("Test!");
nodeInfo.recycle();
for (AccessibilityNodeInfo item : button) {
Log.i(TAG, "long-click button!");
// 執行長按操作
item.performAction(AccessibilityNodeInfo.ACTION_LONG_CLICK);
}
}
break;
default:
break;
}
}
@Override
public void onInterrupt() {
Log.i(TAG, "onInterrupt");
}
}
複製程式碼AccessibilityService配置
res/xml/accessibility_service_config.xml
<?xml version="1.0" encoding="utf-8"?>
<accessibility-service xmlns:android="http://schemas.android.com/apk/res/android"
android:accessibilityEventTypes="typeAllMask"
android:accessibilityFeedbackType="feedbackSpoken"
android:accessibilityFlags="flagRetrieveInteractiveWindows|flagRequestFilterKeyEvents"
android:canRequestFilterKeyEvents="true"
android:canRetrieveWindowContent="true"
android:description="@string/app_name"
android:notificationTimeout="100"
android:packageNames="com.xu.accessibilitydemo" />
複製程式碼在manifest中進行註冊
<service
android:name=".MyAccessibilityService"
android:enabled="true"
android:exported="true"
android:permission="android.permission.BIND_ACCESSIBILITY_SERVICE">
<intent-filter>
<action android:name="android.accessibilityservice.AccessibilityService"/>
</intent-filter>
<meta-data
android:name="android.accessibilityservice"
android:resource="@xml/accessibility_service_config"/>
</service>
複製程式碼建立一個text為Test!的button控制元件，設定監聽方法
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = findViewById(R.id.button);
button.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
Log.i(TAG, "onLongClick");
return false;
}
});
}
}
複製程式碼開啟AccessibilityService
AccessibilityService服務具體開啟位置在設定--無障礙中。
執行應用，點選text為Test!的按鈕
會出現以下的日誌：
具體解釋： 點選按鈕即產生TYPE_VIEW_CLICKED事件 --> 被AcceesibilityService捕獲 --> 捕獲後執行長按按鈕操作 --> 執行長按回撥方法。
為什麼AcceesibilityService能捕獲並執行其他操作呢，接下來我將對原始碼進行解析~
三、原始碼解析
AccessibilityService內部邏輯
AccessibilityService.java
public abstract class AccessibilityService extends Service {
// 省略程式碼
public abstract void onAccessibilityEvent(AccessibilityEvent event);
public abstract void onInterrupt();
@Override
public final IBinder onBind(Intent intent) {
return new IAccessibilityServiceClientWrapper(this, getMainLooper(), new Callbacks() {
@Override
public void onServiceConnected() {
AccessibilityService.this.dispatchServiceConnected();
}
@Override
public void onInterrupt() {
AccessibilityService.this.onInterrupt();
}
@Override
public void onAccessibilityEvent(AccessibilityEvent event) {
AccessibilityService.this.onAccessibilityEvent(event);
}
@Override
public void init(int connectionId, IBinder windowToken) {
mConnectionId = connectionId;
mWindowToken = windowToken;
// The client may have already obtained the window manager, so
// update the default token on whatever manager we gave them.
final WindowManagerImpl wm = (WindowManagerImpl) getSystemService(WINDOW_SERVICE);
wm.setDefaultToken(windowToken);
}
@Override
public boolean onGesture(int gestureId) {
return AccessibilityService.this.onGesture(gestureId);
}
@Override
public boolean onKeyEvent(KeyEvent event) {
return AccessibilityService.this.onKeyEvent(event);
}
@Override
public void onMagnificationChanged(@NonNull Region region,
float scale, float centerX, float centerY) {
AccessibilityService.this.onMagnificationChanged(region, scale, centerX, centerY);
}
@Override
public void onSoftKeyboardShowModeChanged(int showMode) {
AccessibilityService.this.onSoftKeyboardShowModeChanged(showMode);
}
@Override
public void onPerformGestureResult(int sequence, boolean completedSuccessfully) {
AccessibilityService.this.onPerformGestureResult(sequence, completedSuccessfully);
}
});
}
}
複製程式碼分析：
- AccessibilityService是一個抽象類，繼承於Service，提供兩個抽象方法 onAccessibilityEvent() 和 onInterrupt()；
- 雖然是抽象類，但是實現了最重要的 onBind() 方法，在其中建立了一個IAccessibilityServiceClientWrapper物件，實現Callbacks介面中的抽象方法。
IAccessibilityServiceClientWrapper
// 以分析onAccessibilityEvent為例，省略部分程式碼
public static class IAccessibilityServiceClientWrapper extends IAccessibilityServiceClient.Stub
implements HandlerCaller.Callback {
private final HandlerCaller mCaller;
private final Callbacks mCallback;
private int mConnectionId;
public IAccessibilityServiceClientWrapper(Context context, Looper looper,
Callbacks callback) {
mCallback = callback;
mCaller = new HandlerCaller(context, looper, this, true /*asyncHandler*/);
}
public void init(IAccessibilityServiceConnection connection, int connectionId,
IBinder windowToken) {
Message message = mCaller.obtainMessageIOO(DO_INIT, connectionId,
connection, windowToken);
mCaller.sendMessage(message);
}
// 省略部分程式碼
public void onAccessibilityEvent(AccessibilityEvent event) {
Message message = mCaller.obtainMessageO(DO_ON_ACCESSIBILITY_EVENT, event);
mCaller.sendMessage(message);
}
@Override
public void executeMessage(Message message) {
switch (message.what) {
case DO_ON_ACCESSIBILITY_EVENT: {
AccessibilityEvent event = (AccessibilityEvent) message.obj;
if (event != null) {
AccessibilityInteractionClient.getInstance().onAccessibilityEvent(event);
mCallback.onAccessibilityEvent(event);
// Make sure the event is recycled.
try {
event.recycle();
} catch (IllegalStateException ise) {
/* ignore - best effort */
}
}
} return;
// ...
}
}
}
複製程式碼分析：
- IAccessibilityServiceClientWrapper繼承於IAccessibilityServiceClient類，它是一個aidl介面，同時注意到它是繼承於IAccessibilityServiceClient.Stub類，可以大概猜測到，AccessibilityService為一個遠端Service，使用到跨程式通訊技術，後面我還會繼續分析這個；
- IAccessibilityServiceClientWrapper的類構造方法中，有兩個比較重要的引數，一個是looper，另一個是Callbacks callback。Looper不用說，而Callbacks介面定義了很多方法，程式碼如下：
public interface Callbacks {
public void onAccessibilityEvent(AccessibilityEvent event);
public void onInterrupt();
public void onServiceConnected();
public void init(int connectionId, IBinder windowToken);
public boolean onGesture(int gestureId);
public boolean onKeyEvent(KeyEvent event);
public void onMagnificationChanged(@NonNull Region region,
float scale, float centerX, float centerY);
public void onSoftKeyboardShowModeChanged(int showMode);
public void onPerformGestureResult(int sequence, boolean completedSuccessfully);
}
複製程式碼- IAccessibilityServiceClientWrapper同時也實現了HandlerCaller.Callback介面，HandlerCaller類通過命名也可以知道，它內部含有一個Handler例項，所以可以把它當做一個Handler，而處理資訊的方法就是HandlerCaller.Callback#executeMessage(msg)方法
- 程式碼有點繞，故簡單總結一下流程： AccessibilityEvent產生 -> Binder驅動 -> IAccessibilityServiceClientWrapper#onAccessibilityEvent(AccessibilityEvent) -> HandlerCaller#sendMessage(message); // message中包括AccessibilityEvent -> IAccessibilityServiceClientWrapper#executeMessage(); -> Callbacks#onAccessibilityEvent(event); -> AccessibilityService.this.onAccessibilityEvent(event);
到這裡解決了我們的第一個問題：AccessibilityService同樣繼承於Service類，它屬於遠端服務類，是Android系統提供的一種服務，可以繫結此服務，用於捕捉介面的一些特定事件。
AccessibilityService外部邏輯
前面分析了接收到AccessibilityEvent之後的程式碼邏輯，那麼，這些AccessibilityEvent是怎樣產生的呢，而且，在回撥執行之後是怎麼做到點選等操作的（如demo所示）？我們接下來繼續分析相關的原始碼~
我們從demo作為例子開始入手，首先我們知道，一個點選事件的產生，實際程式碼邏輯是在View#onTouchEvent() -> View#performClick()中：
public boolean performClick() {
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);
return result;
}
複製程式碼這裡找到一個重點方法sendAccessibilityEvent()，繼續跟進去，最後走到View#sendAccessibilityEventUncheckedInternal()方法：
public void sendAccessibilityEventUncheckedInternal(AccessibilityEvent event) {
if (!isShown()) {
return;
}
onInitializeAccessibilityEvent(event);
// Only a subset of accessibility events populates text content.
if ((event.getEventType() & POPULATING_ACCESSIBILITY_EVENT_TYPES) != 0) {
dispatchPopulateAccessibilityEvent(event);
}
// In the beginning we called #isShown(), so we know that getParent() is not null.
getParent().requestSendAccessibilityEvent(this, event);
}
複製程式碼這裡的getParent()會返回一個實現ViewParent介面的物件。 我們可以簡單理解為，它會讓View的父類執行requestSendAccessibilityEvent()方法，而View的父類一般為ViewGroup，我們檢視ViewGroup#requestSendAccessibilityEvent()方法
@Override
public boolean requestSendAccessibilityEvent(View child, AccessibilityEvent event) {
ViewParent parent = mParent;
if (parent == null) {
return false;
}
final boolean propagate = onRequestSendAccessibilityEvent(child, event);
if (!propagate) {
return false;
}
return parent.requestSendAccessibilityEvent(this, event);
}
複製程式碼這裡涉及到一個變數mParent，我們要找到這個mParent變數是在哪裡被賦值的。 首先我們在View類中找到一個相關的方法View#assignParent()：
void assignParent(ViewParent parent) {
if (mParent == null) {
mParent = parent;
} else if (parent == null) {
mParent = null;
} else {
throw new RuntimeException("view " + this + " being added, but" + " it already has a parent");
}
}
複製程式碼但是View類中並沒有呼叫此方法，猜測是View的父類進行呼叫。 通過對原始碼進行搜尋，發現最後是在ViewRootImpl#setView()中進行呼叫，賦值的是this即ViewRootImpl本身。 直接跳到ViewRootImpl#requestSendAccessibilityEvent()方法：
@Override
public boolean requestSendAccessibilityEvent(View child, AccessibilityEvent event) {
if (mView == null || mStopped || mPausedForTransition) {
return false;
}
// Intercept accessibility focus events fired by virtual nodes to keep
// track of accessibility focus position in such nodes.
final int eventType = event.getEventType();
switch (eventType) {
case AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUSED:
{
final long sourceNodeId = event.getSourceNodeId();
final int accessibilityViewId = AccessibilityNodeInfo.getAccessibilityViewId(sourceNodeId);
View source = mView.findViewByAccessibilityId(accessibilityViewId);
if (source != null) {
AccessibilityNodeProvider provider = source.getAccessibilityNodeProvider();
if (provider != null) {
final int virtualNodeId = AccessibilityNodeInfo.getVirtualDescendantId(sourceNodeId);
final AccessibilityNodeInfo node;
if (virtualNodeId == AccessibilityNodeInfo.UNDEFINED_ITEM_ID) {
node = provider.createAccessibilityNodeInfo(AccessibilityNodeProvider.HOST_VIEW_ID);
} else {
node = provider.createAccessibilityNodeInfo(virtualNodeId);
}
setAccessibilityFocus(source, node);
}
}
}
break;
// 省略部分程式碼
}
// ！！！
mAccessibilityManager.sendAccessibilityEvent(event);
return true;
}
複製程式碼重點：AccessibilityManager#sendAccessibilityEvent(event)
public void sendAccessibilityEvent(AccessibilityEvent event) {
final IAccessibilityManager service;
final int userId;
synchronized(mLock) {
service = getServiceLocked();
if (service == null) {
return;
}
if (!mIsEnabled) {
Looper myLooper = Looper.myLooper();
if (myLooper == Looper.getMainLooper()) {
throw new IllegalStateException("Accessibility off. Did you forget to check that?");
} else {
// If we're not running on the thread with the main looper, it's possible for
// the state of accessibility to change between checking isEnabled and
// calling this method. So just log the error rather than throwing the
// exception.
Log.e(LOG_TAG, "AccessibilityEvent sent with accessibility disabled");
return;
}
}
userId = mUserId;
}
boolean doRecycle = false;
try {
event.setEventTime(SystemClock.uptimeMillis());
// it is possible that this manager is in the same process as the service but
// client using it is called through Binder from another process. Example: MMS
// app adds a SMS notification and the NotificationManagerService calls this method
long identityToken = Binder.clearCallingIdentity();
// ！！！
doRecycle = service.sendAccessibilityEvent(event, userId);
Binder.restoreCallingIdentity(identityToken);
if (DEBUG) {
Log.i(LOG_TAG, event + " sent");
}
} catch (RemoteException re) {
Log.e(LOG_TAG, "Error during sending " + event + " ", re);
} finally {
if (doRecycle) {
event.recycle();
}
}
}
private IAccessibilityManager getServiceLocked() {
if (mService == null) {
tryConnectToServiceLocked(null);
}
return mService;
}
private void tryConnectToServiceLocked(IAccessibilityManager service) {
if (service == null) {
IBinder iBinder = ServiceManager.getService(Context.ACCESSIBILITY_SERVICE);
if (iBinder == null) {
return;
}
service = IAccessibilityManager.Stub.asInterface(iBinder);
}
try {
final int stateFlags = service.addClient(mClient, mUserId);
setStateLocked(stateFlags);
mService = service;
} catch (RemoteException re) {
Log.e(LOG_TAG, "AccessibilityManagerService is dead", re);
}
}
複製程式碼這裡有使用到Android Binder機制，重點為IAccessibilityManager#sendAccessibilityEvent()方法，這裡呼叫的是代理方法，實際程式碼邏輯在AccessibilityManagerService#sendAccessibilityEvent()：
@Override
public boolean sendAccessibilityEvent(AccessibilityEvent event, int userId) {
synchronized(mLock) {
// We treat calls from a profile as if made by its parent as profiles
// share the accessibility state of the parent. The call below
// performs the current profile parent resolution..
final int resolvedUserId = mSecurityPolicy.resolveCallingUserIdEnforcingPermissionsLocked(userId);
// This method does nothing for a background user.
if (resolvedUserId != mCurrentUserId) {
return true; // yes, recycle the event
}
if (mSecurityPolicy.canDispatchAccessibilityEventLocked(event)) {
mSecurityPolicy.updateActiveAndAccessibilityFocusedWindowLocked(event.getWindowId(), event.getSourceNodeId(), event.getEventType(), event.getAction());
mSecurityPolicy.updateEventSourceLocked(event);
// ！！！
notifyAccessibilityServicesDelayedLocked(event, false);
notifyAccessibilityServicesDelayedLocked(event, true);
}
if (mHasInputFilter && mInputFilter != null) {
mMainHandler.obtainMessage(MainHandler.MSG_SEND_ACCESSIBILITY_EVENT_TO_INPUT_FILTER, AccessibilityEvent.obtain(event)).sendToTarget();
}
event.recycle();
}
return (OWN_PROCESS_ID != Binder.getCallingPid());
}
private void notifyAccessibilityServicesDelayedLocked(AccessibilityEvent event, boolean isDefault) {
try {
UserState state = getCurrentUserStateLocked();
for (int i = 0, count = state.mBoundServices.size(); i < count; i++) {
Service service = state.mBoundServices.get(i);
if (service.mIsDefault == isDefault) {
if (canDispatchEventToServiceLocked(service, event)) {
service.notifyAccessibilityEvent(event);
}
}
}
} catch (IndexOutOfBoundsException oobe) {
// An out of bounds exception can happen if services are going away
// as the for loop is running. If that happens, just bail because
// there are no more services to notify.
}
}
複製程式碼- 在方法中，最後會呼叫notifyAccessibilityServicesDelayedLocked()方法，然後將event進行回收；
- 在notifyAccessibilityServicesDelayedLocked()方法中，會獲得所有Bound即繫結的Service，執行notifyAccessibilityEvent()方法，通過跟蹤程式碼邏輯，最後會呼叫繫結Service的onAccessibilityEvent()方法。繫結的Service是指我們自己實現的繼承於AccessibilityService的Service類，當你在設定-無障礙中開啟服務之後即將服務繫結到AccessibilityManagerService中。
這樣我們解決了第二個問題： AccessibilityService是如何做到監控捕捉使用者行為的：（以點選事件為例） AccessibilityEvent產生： View#performClick() -> View#sendAccessibilityEventUncheckedInternal() -> ViewGroup#requestSendAccessibilityEvent() -> ViewRootImpl#requestSendAccessibilityEvent() -> AccessibilityManager#sendAccessibilityEvent(event) -> AccessibilityManagerService#sendAccessibilityEvent() -> AccessibilityManagerService#notifyAccessibilityServicesDelayedLocked() -> Service#notifyAccessibilityEvent(event)
AccessibilityEvent處理： AccessibilityEvent -> Binder驅動 -> IAccessibilityServiceClientWrapper#onAccessibilityEvent(AccessibilityEvent) -> HandlerCaller#sendMessage(message); // message中包括AccessibilityEvent -> IAccessibilityServiceClientWrapper#executeMessage(); -> Callbacks#onAccessibilityEvent(event); -> AccessibilityService.this.onAccessibilityEvent(event);
AccessibilityService互動之查詢控制元件
在demo中，我們在MyAccessibilityService中呼叫了getRootInActiveWindow()方法獲取被監控的View的所有結點，這些結點都封裝成一個AccessibilityNodeInfo物件中。同時也呼叫AccessibilityNodeInfo#findAccessibilityNodeInfosByText()方法查詢相應的控制元件。 這些方法的本質是呼叫了AccessibilityInteractionClient類的對應方法。 以AccessibilityInteractionClient#findAccessibilityNodeInfosByText()為例：
public List<AccessibilityNodeInfo> findAccessibilityNodeInfosByText(int connectionId, int accessibilityWindowId, long accessibilityNodeId, String text) {
try {
IAccessibilityServiceConnection connection = getConnection(connectionId);
if (connection != null) {
final int interactionId = mInteractionIdCounter.getAndIncrement();
final long identityToken = Binder.clearCallingIdentity();
final boolean success = connection.findAccessibilityNodeInfosByText(accessibilityWindowId, accessibilityNodeId, text, interactionId, this, Thread.currentThread().getId());
Binder.restoreCallingIdentity(identityToken);
if (success) {
List<AccessibilityNodeInfo> infos = getFindAccessibilityNodeInfosResultAndClear(interactionId);
if (infos != null) {
finalizeAndCacheAccessibilityNodeInfos(infos, connectionId);
return infos;
}
}
} else {
if (DEBUG) {
Log.w(LOG_TAG, "No connection for connection id: " + connectionId);
}
}
} catch (RemoteException re) {
Log.w(LOG_TAG, "Error while calling remote" + " findAccessibilityNodeInfosByViewText", re);
}
return Collections.emptyList();
}
複製程式碼程式碼邏輯比較簡單，就是直接呼叫IAccessibilityServiceConnection#findAccessibilityNodeInfosByText()方法。 IAccessibilityServiceConnection是一個aidl介面，從註釋看，它是AccessibilitySerivce和AccessibilityManagerService之間溝通的橋樑。 猜想程式碼真正的實現在AccessibilityManagerService中。 AccessibilityManagerService.Service#findAccessibilityNodeInfosByText()：
@Override
public boolean findAccessibilityNodeInfosByText(int accessibilityWindowId, long accessibilityNodeId, String text, int interactionId, IAccessibilityInteractionConnectionCallback callback, long interrogatingTid) throws RemoteException {
final int resolvedWindowId;
IAccessibilityInteractionConnection connection = null;
Region partialInteractiveRegion = Region.obtain();
synchronized(mLock) {
if (!isCalledForCurrentUserLocked()) {
return false;
}
resolvedWindowId = resolveAccessibilityWindowIdLocked(accessibilityWindowId);
final boolean permissionGranted = mSecurityPolicy.canGetAccessibilityNodeInfoLocked(this, resolvedWindowId);
if (!permissionGranted) {
return false;
} else {
connection = getConnectionLocked(resolvedWindowId);
if (connection == null) {
return false;
}
}
if (!mSecurityPolicy.computePartialInteractiveRegionForWindowLocked(resolvedWindowId, partialInteractiveRegion)) {
partialInteractiveRegion.recycle();
partialInteractiveRegion = null;
}
}
final int interrogatingPid = Binder.getCallingPid();
final long identityToken = Binder.clearCallingIdentity();
MagnificationSpec spec = getCompatibleMagnificationSpecLocked(resolvedWindowId);
try {
connection.findAccessibilityNodeInfosByText(accessibilityNodeId, text, partialInteractiveRegion, interactionId, callback, mFetchFlags, interrogatingPid, interrogatingTid, spec);
return true;
} catch (RemoteException re) {
if (DEBUG) {
Slog.e(LOG_TAG, "Error calling findAccessibilityNodeInfosByText()");
}
} finally {
Binder.restoreCallingIdentity(identityToken);
// Recycle if passed to another process.
if (partialInteractiveRegion != null && Binder.isProxy(connection)) {
partialInteractiveRegion.recycle();
}
}
return false;
}
複製程式碼- 此方法在AccessibilityManagerService的內部類Service中實現，這個Service繼承於IAccessibilityServiceConnection.Stub，驗證了我上面的猜想是正確的；
- 程式碼重點是呼叫connection.findAccessibilityNodeInfosByText()，這裡的connection例項與上面不同，它隸屬於IAccessibilityInteractionConnection類。這個類同樣是一個aidl介面，從註釋上看，它又是AccessibilityManagerService與指定視窗的ViewRoot之間溝通的橋樑。 再次猜想，真正的程式碼邏輯在ViewRootImpl中。 檢視ViewRootImpl.AccessibilityInteractionConnection#findAccessibilityNodeInfosByText()：
@Override
public void findAccessibilityNodeInfosByText(long accessibilityNodeId, String text, Region interactiveRegion, int interactionId, IAccessibilityInteractionConnectionCallback callback, int flags, int interrogatingPid, long interrogatingTid, MagnificationSpec spec) {
ViewRootImpl viewRootImpl = mViewRootImpl.get();
if (viewRootImpl != null && viewRootImpl.mView != null) {
viewRootImpl.getAccessibilityInteractionController().findAccessibilityNodeInfosByTextClientThread(accessibilityNodeId, text, interactiveRegion, interactionId, callback, flags, interrogatingPid, interrogatingTid, spec);
} else {
// We cannot make the call and notify the caller so it does not wait.
try {
callback.setFindAccessibilityNodeInfosResult(null, interactionId);
} catch (RemoteException re) {
/* best effort - ignore */
}
}
}
複製程式碼- 同樣的，此方法在ViewRootImpl的內部類AccessibilityInteractionConnection中實現，這個內部類繼承於IAccessibilityServiceConnection.Stub，驗證了我的猜想；
- 查詢控制元件等操作，ViewRootImpl並不是直接處理，而是交給AccessibilityInteractionController類去查詢，查詢到的結果會儲存到一個callback中，這個callback為IAccessibilityInteractionConnectionCallback型別，它也是一個aidl介面，而AccessibilityInteractionClient類繼承了IAccessibilityInteractionConnectionCallback.Stub，即最後查詢後的結果會回撥到AccessibilityInteractionClient類中，如上面AccessibilityInteractionClient#findAccessibilityNodeInfosByText()方法，最後會呼叫getFindAccessibilityNodeInfosResultAndClear()方法獲取結果。具體如何尋找指定控制元件則不再分析程式碼。
AccessibilityService互動之執行控制元件操作
類似的，與上面的流程基本相同，只是回撥的時候，返回的是執行操作的返回值（True or False）。
到這裡，我們解決了最後一個問題： AccessibilityService是如何做到查詢控制元件，執行點選等操作的？ 總結： 尋找指定控制元件/執行操作 -> 交給AccessibilityInteractionClient類處理 -> Binder -> AccessibilityManagerService類進行查詢/執行操作 -> Binder -> 指定視窗的ViewRoot（ViewRootImpl）進行查詢/執行操作 <- Binder <- 結果回撥到AccessibilityInteractionClient類
四、有用程式碼記錄
- HandlerCaller類：結合Handler類和自定義的介面類（Caller.java），利用Handler的訊息迴圈機制來分發訊息，將最終的處理函式交給Caller#executeMessage()：
// HandlerCaller.java
public class HandlerCaller {
final Looper mMainLooper;
final Handler mH;
final Callback mCallback;
class MyHandler extends Handler {
MyHandler(Looper looper, boolean async) {
super(looper, null, async);
}
@Override
public void handleMessage(Message msg) {
mCallback.executeMessage(msg);
}
}
public interface Callback {
public void executeMessage(Message msg);
}
public HandlerCaller(Context context, Looper looper, Callback callback,
boolean asyncHandler) {
mMainLooper = looper != null ? looper : context.getMainLooper();
mH = new MyHandler(mMainLooper, asyncHandler);
mCallback = callback;
}
public Handler getHandler() {
return mH;
}
public void executeOrSendMessage(Message msg) {
// If we are calling this from the main thread, then we can call
// right through. Otherwise, we need to send the message to the
// main thread.
if (Looper.myLooper() == mMainLooper) {
mCallback.executeMessage(msg);
msg.recycle();
return;
}
mH.sendMessage(msg);
}
public void sendMessageDelayed(Message msg, long delayMillis) {
mH.sendMessageDelayed(msg, delayMillis);
}
public boolean hasMessages(int what) {
return mH.hasMessages(what);
}
public void removeMessages(int what) {
mH.removeMessages(what);
}
public void removeMessages(int what, Object obj) {
mH.removeMessages(what, obj);
}
public void sendMessage(Message msg) {
mH.sendMessage(msg);
}
public SomeArgs sendMessageAndWait(Message msg) {
if (Looper.myLooper() == mH.getLooper()) {
throw new IllegalStateException("Can't wait on same thread as looper");
}
SomeArgs args = (SomeArgs)msg.obj;
args.mWaitState = SomeArgs.WAIT_WAITING;
mH.sendMessage(msg);
synchronized (args) {
while (args.mWaitState == SomeArgs.WAIT_WAITING) {
try {
args.wait();
} catch (InterruptedException e) {
return null;
}
}
}
args.mWaitState = SomeArgs.WAIT_NONE;
return args;
}
public Message obtainMessage(int what) {
return mH.obtainMessage(what);
}
// 省略部分程式碼
}
複製程式碼- HandlerCaller#sendMessageAndWait()：
public SomeArgs sendMessageAndWait(Message msg) {
if (Looper.myLooper() == mH.getLooper()) {
throw new IllegalStateException("Can't wait on same thread as looper");
}
SomeArgs args = (SomeArgs) msg.obj;
args.mWaitState = SomeArgs.WAIT_WAITING;
mH.sendMessage(msg);
synchronized(args) {
while (args.mWaitState == SomeArgs.WAIT_WAITING) {
try {
args.wait();
} catch (InterruptedException e) {
return null;
}
}
}
args.mWaitState = SomeArgs.WAIT_NONE;
return args;
}
複製程式碼這篇文章會同步到我的個人日誌，如有問題，請大家踴躍提出，謝謝大家！