Use Looper.getMainLooper() in Handler constructors in ExoPlayer when needed.

Looper.myLooper(), the default looper, may be null in background threads. This adds a fallback to use the main app looper.

This will allow ExoPlayer instances to be built in background threads in Photos.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=154845446

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java

@@ -15,6 +15,7 @@
  */
 package com.google.android.exoplayer2;
 
+import android.os.Looper;
 import android.support.annotation.IntDef;
 import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.audio.MediaCodecAudioRenderer;
@@ -91,7 +92,9 @@ import java.lang.annotation.RetentionPolicy;
  * thread. The application's main thread is ideal. Accessing an instance from multiple threads is
  * discouraged, however if an application does wish to do this then it may do so provided that it
  * ensures accesses are synchronized.</li>
- * <li>Registered listeners are called on the thread that created the ExoPlayer instance.</li>
+ * <li>Registered listeners are called on the thread that created the ExoPlayer instance, unless
+ * the thread that created the ExoPlayer instance does not have a {@link Looper}. In that case,
+ * registered listeners will be called on the application's main thread.</li>
  * <li>An internal playback thread is responsible for playback. Injected player components such as
  * Renderers, MediaSources, TrackSelectors and LoadControls are called by the player on this
  * thread.</li>
@@ -267,7 +270,8 @@ public interface ExoPlayer {
 
   /**
    * Register a listener to receive events from the player. The listener's methods will be called on
-   * the thread that was used to construct the player.
+   * the thread that was used to construct the player. However, if the thread used to construct the
+   * player does not have a {@link Looper}, then the listener will be called on the main thread.
    *
    * @param listener The listener to register.
    */

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java

@@ -16,7 +16,6 @@
 package com.google.android.exoplayer2;
 
 import android.content.Context;
-import android.os.Looper;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.drm.FrameworkMediaCrypto;
 import com.google.android.exoplayer2.trackselection.TrackSelector;
@@ -29,8 +28,7 @@ public final class ExoPlayerFactory {
   private ExoPlayerFactory() {}
 
   /**
-   * Creates a {@link SimpleExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates a {@link SimpleExoPlayer} instance.
    *
    * @param context A {@link Context}.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -45,8 +43,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates a {@link SimpleExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}. Available extension renderers are not used.
+   * Creates a {@link SimpleExoPlayer} instance. Available extension renderers are not used.
    *
    * @param context A {@link Context}.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -63,8 +60,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates a {@link SimpleExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates a {@link SimpleExoPlayer} instance.
    *
    * @param context A {@link Context}.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -86,8 +82,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates a {@link SimpleExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates a {@link SimpleExoPlayer} instance.
    *
    * @param context A {@link Context}.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -112,8 +107,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates a {@link SimpleExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates a {@link SimpleExoPlayer} instance.
    *
    * @param context A {@link Context}.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -123,8 +117,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates a {@link SimpleExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates a {@link SimpleExoPlayer} instance.
    *
    * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -135,8 +128,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates a {@link SimpleExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates a {@link SimpleExoPlayer} instance.
    *
    * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -148,8 +140,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates an {@link ExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates an {@link ExoPlayer} instance.
    *
    * @param renderers The {@link Renderer}s that will be used by the instance.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
@@ -159,8 +150,7 @@ public final class ExoPlayerFactory {
   }
 
   /**
-   * Creates an {@link ExoPlayer} instance. Must be called from a thread that has an associated
-   * {@link Looper}.
+   * Creates an {@link ExoPlayer} instance.
    *
    * @param renderers The {@link Renderer}s that will be used by the instance.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java

@@ -92,7 +92,8 @@ import java.util.concurrent.CopyOnWriteArraySet;
     trackGroups = TrackGroupArray.EMPTY;
     trackSelections = emptyTrackSelections;
     playbackParameters = PlaybackParameters.DEFAULT;
-    eventHandler = new Handler() {
+    Looper eventLooper = Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper();
+    eventHandler = new Handler(eventLooper) {
       @Override
       public void handleMessage(Message msg) {
         ExoPlayerImpl.this.handleEvent(msg);

library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java

@@ -20,6 +20,7 @@ import android.graphics.SurfaceTexture;
 import android.media.MediaCodec;
 import android.media.PlaybackParams;
 import android.os.Handler;
+import android.os.Looper;
 import android.support.annotation.Nullable;
 import android.util.Log;
 import android.view.Surface;
@@ -111,8 +112,10 @@ public class SimpleExoPlayer implements ExoPlayer {
   protected SimpleExoPlayer(RenderersFactory renderersFactory, TrackSelector trackSelector,
       LoadControl loadControl) {
     componentListener = new ComponentListener();
-    renderers = renderersFactory.createRenderers(new Handler(), componentListener,
-        componentListener, componentListener, componentListener);
+    Looper eventLooper = Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper();
+    Handler eventHandler = new Handler(eventLooper);
+    renderers = renderersFactory.createRenderers(eventHandler, componentListener, componentListener,
+        componentListener, componentListener);
 
     // Obtain counts of video and audio renderers.
     int videoRendererCount = 0;