SystemMediaRoute2Provider: Set callback after instantiation is done

A NullPointerException can happen if some callback method is called
before the constructor of SystemMediaRoute2Provider ends.
This CL fixes the issue.

Bug: 158838070
Test: Passes CTS and mediaroutertest
Change-Id: Ibad3c54ad3f7921621628b6147c35605652da29b

services/core/java/com/android/server/media/MediaRouter2ServiceImpl.java

@@ -985,6 +985,7 @@ class MediaRouter2ServiceImpl {
         if (userRecord == null) {
             userRecord = new UserRecord(userId);
             mUserRecords.put(userId, userRecord);
+            userRecord.init();
             if (userId == mCurrentUserId) {
                 userRecord.mHandler.sendMessage(
                         obtainMessage(UserHandler::start, userRecord.mHandler));
@@ -1034,6 +1035,10 @@ class MediaRouter2ServiceImpl {
             mHandler = new UserHandler(MediaRouter2ServiceImpl.this, this);
         }
 
+        void init() {
+            mHandler.init();
+        }
+
         // TODO: This assumes that only one router exists in a package.
         //       Do this in Android S or later.
         RouterRecord findRouterRecordLocked(String packageName) {
@@ -1141,16 +1146,21 @@ class MediaRouter2ServiceImpl {
 
         private boolean mRunning;
 
+        // TODO: (In Android S+) Pull out SystemMediaRoute2Provider out of UserHandler.
         UserHandler(@NonNull MediaRouter2ServiceImpl service, @NonNull UserRecord userRecord) {
             super(Looper.getMainLooper(), null, true);
             mServiceRef = new WeakReference<>(service);
             mUserRecord = userRecord;
-            mSystemProvider = new SystemMediaRoute2Provider(service.mContext, this);
+            mSystemProvider = new SystemMediaRoute2Provider(service.mContext);
             mRouteProviders.add(mSystemProvider);
             mWatcher = new MediaRoute2ProviderWatcher(service.mContext, this,
                     this, mUserRecord.mUserId);
         }
 
+        void init() {
+            mSystemProvider.setCallback(this);
+        }
+
         private void start() {
             if (!mRunning) {
                 mRunning = true;

services/core/java/com/android/server/media/SystemMediaRoute2Provider.java

@@ -98,12 +98,10 @@ class SystemMediaRoute2Provider extends MediaRoute2Provider {
         }
     };
 
-    SystemMediaRoute2Provider(Context context, Callback callback) {
+    SystemMediaRoute2Provider(Context context) {
         super(sComponentName);
-        setCallback(callback);
 
         mIsSystemRouteProvider = true;
-
         mContext = context;
         mHandler = new Handler(Looper.getMainLooper());
 
@@ -142,6 +140,13 @@ class SystemMediaRoute2Provider extends MediaRoute2Provider {
         updateVolume();
     }
 
+    @Override
+    public void setCallback(Callback callback) {
+        super.setCallback(callback);
+        notifyProviderState();
+        notifySessionInfoUpdated();
+    }
+
     @Override
     public void requestCreateSession(long requestId, String packageName, String routeId,
             Bundle sessionHints) {
@@ -354,6 +359,10 @@ class SystemMediaRoute2Provider extends MediaRoute2Provider {
     }
 
     void notifySessionInfoUpdated() {
+        if (mCallback == null) {
+            return;
+        }
+
         RoutingSessionInfo sessionInfo;
         synchronized (mLock) {
             sessionInfo = mSessionInfos.get(0);