Use CastContextWrapper in MediaRouteButtonFactory

Migrate the MediaRouteButtonFactory to use the CastContextWrapper
class. Due to the async initialization of the CastContext, the
MediaRouteButtonFactory registers listeners to the CastContextWrapper
for monitoring the initialization of the Cast Context.

PiperOrigin-RevId: 846794943

Author: Googler

libraries/cast/src/main/java/androidx/media3/cast/CastContextWrapper.java

@@ -15,24 +15,28 @@
  */
 package androidx.media3.cast;
 
+import static androidx.media3.cast.CastUtils.verifyMainThread;
+import static com.google.common.base.Preconditions.checkNotNull;
+
 import android.annotation.SuppressLint;
 import android.content.Context;
-import android.os.Looper;
 import androidx.annotation.MainThread;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
-import androidx.core.util.Preconditions;
 import androidx.media3.common.util.BackgroundExecutor;
 import androidx.media3.common.util.Log;
 import androidx.media3.common.util.UnstableApi;
+import androidx.mediarouter.media.MediaRouteSelector;
 import com.google.android.gms.cast.framework.CastContext;
 import com.google.android.gms.cast.framework.CastSession;
 import com.google.android.gms.cast.framework.SessionManager;
 import com.google.android.gms.cast.framework.SessionManagerListener;
 import com.google.android.gms.tasks.Task;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
 /**
@@ -54,14 +58,17 @@ public class CastContextWrapper {
   @Nullable
   private static CastContextWrapper singletonInstance;
 
-  @Nullable private CastContext castContext;
   private final List<SessionManagerListener<CastSession>> pendingListeners;
+
+  private final Set<MediaRouteSelectorListener> pendingMediaRouteSelectorListeners;
+
+  @Nullable private CastContext castContext;
   private @MonotonicNonNull Throwable castContextLoadFailure;
   private boolean isInitOngoing;
 
   /** Returns a singleton instance of {@link CastContextWrapper}. */
   public static CastContextWrapper getSingletonInstance() {
-    checkRunningOnMainThread();
+    verifyMainThread();
     if (singletonInstance == null) {
       singletonInstance = new CastContextWrapper();
     }
@@ -76,8 +83,8 @@ public static CastContextWrapper getSingletonInstance() {
    */
   @CanIgnoreReturnValue
   public CastContextWrapper initWithContext(CastContext castContext) {
-    checkRunningOnMainThread();
-    Preconditions.checkNotNull(castContext);
+    verifyMainThread();
+    checkNotNull(castContext);
     if (needsInitialization()) {
       setCastContext(castContext);
     }
@@ -99,7 +106,7 @@ public void asyncInit(Context context) {
 
   @VisibleForTesting
   /* package */ void asyncInit(CastContextInitializer castContextInitializer) {
-    checkRunningOnMainThread();
+    verifyMainThread();
     if (!needsInitialization()) {
       Log.w(TAG, "Tried to initialize an already initialized CastContextWrapper.");
       return;
@@ -147,7 +154,7 @@ public Throwable getCastContextLoadFailure() {
    * @param listener The listener to register.
    */
   public void addSessionManagerListener(SessionManagerListener<CastSession> listener) {
-    checkRunningOnMainThread();
+    verifyMainThread();
     if (castContext != null) {
       castContext.getSessionManager().addSessionManagerListener(listener, CastSession.class);
     } else {
@@ -157,21 +164,40 @@ public void addSessionManagerListener(SessionManagerListener<CastSession> listen
 
   /** Unregisters the given session manager listener. */
   public void removeSessionManagerListener(SessionManagerListener<CastSession> listener) {
-    checkRunningOnMainThread();
+    verifyMainThread();
     if (castContext != null) {
       castContext.getSessionManager().removeSessionManagerListener(listener, CastSession.class);
     } else {
       pendingListeners.remove(listener);
     }
   }
 
+  @Nullable
+  /* package */ MediaRouteSelector registerListenerAndGetCurrentSelector(
+      MediaRouteSelectorListener listener) {
+    checkNotNull(listener);
+    if (castContext != null) {
+      MediaRouteSelector selector = castContext.getMergedSelector();
+      return (selector == null) ? MediaRouteSelector.EMPTY : selector;
+    }
+    if (castContextLoadFailure != null) {
+      return MediaRouteSelector.EMPTY;
+    }
+    pendingMediaRouteSelectorListeners.add(listener);
+    return null;
+  }
+
+  /* package */ void unregisterListener(MediaRouteSelectorListener listener) {
+    pendingMediaRouteSelectorListeners.remove(listener);
+  }
+
   /**
    * Returns the ongoing Cast session, or null if there's no ongoing Cast session, or there's no
    * Cast context available.
    */
   @Nullable
   public CastSession getCurrentCastSession() {
-    checkRunningOnMainThread();
+    verifyMainThread();
     return castContext != null ? castContext.getSessionManager().getCurrentCastSession() : null;
   }
 
@@ -181,14 +207,14 @@ public CastSession getCurrentCastSession() {
    * @param stopCasting Whether to stop the receiver application.
    */
   public void endCurrentSession(boolean stopCasting) {
-    checkRunningOnMainThread();
+    verifyMainThread();
     if (castContext != null) {
       castContext.getSessionManager().endCurrentSession(stopCasting);
     }
   }
 
   private void setCastContext(CastContext castContext) {
-    checkRunningOnMainThread();
+    verifyMainThread();
     isInitOngoing = false;
     this.castContext = castContext;
     SessionManager sessionManager = castContext.getSessionManager();
@@ -205,6 +231,9 @@ private void setCastContext(CastContext castContext) {
       }
     }
     pendingListeners.clear();
+    MediaRouteSelector selector = castContext.getMergedSelector();
+    selector = (selector == null) ? MediaRouteSelector.EMPTY : selector;
+    notifyPendingMediaRouteSelectorListeners(selector);
   }
 
   private void onCastContextLoadFailure(@Nullable Exception exception) {
@@ -214,25 +243,36 @@ private void onCastContextLoadFailure(@Nullable Exception exception) {
             ? exception
             : new UnknownError("Cast context load failed with a null exception.");
     Log.e(TAG, "Failed to load CastContext", castContextLoadFailure);
+    // Cast context load has failed, the selector won't become non-empty. Notifying listeners with
+    // an empty selector ensures that listeners are not left pending forever.
+    notifyPendingMediaRouteSelectorListeners(MediaRouteSelector.EMPTY);
+  }
+
+  private void notifyPendingMediaRouteSelectorListeners(MediaRouteSelector selector) {
+    for (MediaRouteSelectorListener listener : pendingMediaRouteSelectorListeners) {
+      listener.onMediaRouteSelectorChanged(selector);
+    }
+    pendingMediaRouteSelectorListeners.clear();
   }
 
   private CastContextWrapper() {
     pendingListeners = new ArrayList<>();
+    pendingMediaRouteSelectorListeners = new HashSet<>();
   }
 
   @VisibleForTesting
   /* package */ static void reset() {
-    checkRunningOnMainThread();
+    verifyMainThread();
     singletonInstance = null;
   }
 
-  private static void checkRunningOnMainThread() {
-    Preconditions.checkState(Looper.myLooper() == Looper.getMainLooper());
-  }
-
   @VisibleForTesting
   /* package */ interface CastContextInitializer {
 
     Task<CastContext> init();
   }
+
+  /* package */ abstract static class MediaRouteSelectorListener {
+    void onMediaRouteSelectorChanged(MediaRouteSelector selector) {}
+  }
 }

libraries/cast/src/main/java/androidx/media3/cast/CastUtils.java

@@ -15,7 +15,9 @@
  */
 package androidx.media3.cast;
 
+import android.os.Looper;
 import androidx.annotation.Nullable;
+import androidx.core.util.Preconditions;
 import androidx.media3.common.C;
 import androidx.media3.common.C.TrackType;
 import androidx.media3.common.Format;
@@ -29,6 +31,15 @@
 /** Utility methods for Cast integration. */
 /* package */ final class CastUtils {
 
+  /**
+   * Verifies that the current thread is the main thread.
+   *
+   * @throws IllegalStateException if the current thread is not the main thread.
+   */
+  public static void verifyMainThread() {
+    Preconditions.checkState(Looper.myLooper() == Looper.getMainLooper());
+  }
+
   /**
    * Returns the duration in microseconds advertised by a media info, or {@link C#TIME_UNSET} if
    * unknown or not applicable.