Factor out Handler creation in construtor to prevent warning suppression.

Using new Handler(this) in a constructor potentially leaks an uninitialized
object. This is mostly not a problem because we don't use the Handler within
the constructor. Added a Util method to keep the warning suppression local.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=199605377

library/core/src/main/java/com/google/android/exoplayer2/metadata/MetadataRenderer.java

@@ -19,12 +19,14 @@ import android.os.Handler;
 import android.os.Handler.Callback;
 import android.os.Looper;
 import android.os.Message;
+import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.BaseRenderer;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.ExoPlaybackException;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.FormatHolder;
 import com.google.android.exoplayer2.util.Assertions;
+import com.google.android.exoplayer2.util.Util;
 import java.util.Arrays;
 
 /**
@@ -46,7 +48,7 @@ public final class MetadataRenderer extends BaseRenderer implements Callback {
 
   private final MetadataDecoderFactory decoderFactory;
   private final MetadataOutput output;
-  private final Handler outputHandler;
+  private final @Nullable Handler outputHandler;
   private final FormatHolder formatHolder;
   private final MetadataInputBuffer buffer;
   private final Metadata[] pendingMetadata;
@@ -61,11 +63,11 @@ public final class MetadataRenderer extends BaseRenderer implements Callback {
    * @param output The output.
    * @param outputLooper The looper associated with the thread on which the output should be called.
    *     If the output makes use of standard Android UI components, then this should normally be the
-   *     looper associated with the application's main thread, which can be obtained using
-   *     {@link android.app.Activity#getMainLooper()}. Null may be passed if the output should be
-   *     called directly on the player's internal rendering thread.
+   *     looper associated with the application's main thread, which can be obtained using {@link
+   *     android.app.Activity#getMainLooper()}. Null may be passed if the output should be called
+   *     directly on the player's internal rendering thread.
    */
-  public MetadataRenderer(MetadataOutput output, Looper outputLooper) {
+  public MetadataRenderer(MetadataOutput output, @Nullable Looper outputLooper) {
     this(output, outputLooper, MetadataDecoderFactory.DEFAULT);
   }
 
@@ -73,16 +75,17 @@ public final class MetadataRenderer extends BaseRenderer implements Callback {
    * @param output The output.
    * @param outputLooper The looper associated with the thread on which the output should be called.
    *     If the output makes use of standard Android UI components, then this should normally be the
-   *     looper associated with the application's main thread, which can be obtained using
-   *     {@link android.app.Activity#getMainLooper()}. Null may be passed if the output should be
-   *     called directly on the player's internal rendering thread.
+   *     looper associated with the application's main thread, which can be obtained using {@link
+   *     android.app.Activity#getMainLooper()}. Null may be passed if the output should be called
+   *     directly on the player's internal rendering thread.
    * @param decoderFactory A factory from which to obtain {@link MetadataDecoder} instances.
    */
-  public MetadataRenderer(MetadataOutput output, Looper outputLooper,
-      MetadataDecoderFactory decoderFactory) {
+  public MetadataRenderer(
+      MetadataOutput output, @Nullable Looper outputLooper, MetadataDecoderFactory decoderFactory) {
     super(C.TRACK_TYPE_METADATA);
     this.output = Assertions.checkNotNull(output);
-    this.outputHandler = outputLooper == null ? null : new Handler(outputLooper, this);
+    this.outputHandler =
+        outputLooper == null ? null : Util.createHandler(outputLooper, /* callback= */ this);
     this.decoderFactory = Assertions.checkNotNull(decoderFactory);
     formatHolder = new FormatHolder();
     buffer = new MetadataInputBuffer();

library/core/src/main/java/com/google/android/exoplayer2/text/TextRenderer.java

@@ -20,6 +20,7 @@ import android.os.Handler.Callback;
 import android.os.Looper;
 import android.os.Message;
 import android.support.annotation.IntDef;
+import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.BaseRenderer;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.ExoPlaybackException;
@@ -27,6 +28,7 @@ import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.FormatHolder;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.MimeTypes;
+import com.google.android.exoplayer2.util.Util;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.util.Collections;
@@ -70,7 +72,7 @@ public final class TextRenderer extends BaseRenderer implements Callback {
 
   private static final int MSG_UPDATE_OUTPUT = 0;
 
-  private final Handler outputHandler;
+  private final @Nullable Handler outputHandler;
   private final TextOutput output;
   private final SubtitleDecoderFactory decoderFactory;
   private final FormatHolder formatHolder;
@@ -87,30 +89,31 @@ public final class TextRenderer extends BaseRenderer implements Callback {
 
   /**
    * @param output The output.
-   * @param outputLooper The looper associated with the thread on which the output should be
-   *     called. If the output makes use of standard Android UI components, then this should
-   *     normally be the looper associated with the application's main thread, which can be obtained
-   *     using {@link android.app.Activity#getMainLooper()}. Null may be passed if the output
-   *     should be called directly on the player's internal rendering thread.
+   * @param outputLooper The looper associated with the thread on which the output should be called.
+   *     If the output makes use of standard Android UI components, then this should normally be the
+   *     looper associated with the application's main thread, which can be obtained using {@link
+   *     android.app.Activity#getMainLooper()}. Null may be passed if the output should be called
+   *     directly on the player's internal rendering thread.
    */
-  public TextRenderer(TextOutput output, Looper outputLooper) {
+  public TextRenderer(TextOutput output, @Nullable Looper outputLooper) {
     this(output, outputLooper, SubtitleDecoderFactory.DEFAULT);
   }
 
   /**
    * @param output The output.
-   * @param outputLooper The looper associated with the thread on which the output should be
-   *     called. If the output makes use of standard Android UI components, then this should
-   *     normally be the looper associated with the application's main thread, which can be obtained
-   *     using {@link android.app.Activity#getMainLooper()}. Null may be passed if the output
-   *     should be called directly on the player's internal rendering thread.
+   * @param outputLooper The looper associated with the thread on which the output should be called.
+   *     If the output makes use of standard Android UI components, then this should normally be the
+   *     looper associated with the application's main thread, which can be obtained using {@link
+   *     android.app.Activity#getMainLooper()}. Null may be passed if the output should be called
+   *     directly on the player's internal rendering thread.
    * @param decoderFactory A factory from which to obtain {@link SubtitleDecoder} instances.
    */
-  public TextRenderer(TextOutput output, Looper outputLooper,
-      SubtitleDecoderFactory decoderFactory) {
+  public TextRenderer(
+      TextOutput output, @Nullable Looper outputLooper, SubtitleDecoderFactory decoderFactory) {
     super(C.TRACK_TYPE_TEXT);
     this.output = Assertions.checkNotNull(output);
-    this.outputHandler = outputLooper == null ? null : new Handler(outputLooper, this);
+    this.outputHandler =
+        outputLooper == null ? null : Util.createHandler(outputLooper, /* callback= */ this);
     this.decoderFactory = decoderFactory;
     formatHolder = new FormatHolder();
   }

library/core/src/main/java/com/google/android/exoplayer2/util/Util.java

@@ -29,6 +29,8 @@ import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 import android.net.Uri;
 import android.os.Build;
+import android.os.Handler;
+import android.os.Looper;
 import android.os.Parcel;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
@@ -66,6 +68,7 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadFactory;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import org.checkerframework.checker.initialization.qual.UnknownInitialization;
 import org.checkerframework.checker.nullness.qual.PolyNull;
 
 /**
@@ -237,13 +240,42 @@ public final class Util {
    * @param length The output array length. Must be less or equal to the length of the input array.
    * @return The copied array.
    */
-  @SuppressWarnings("nullness:assignment.type.incompatible")
+  @SuppressWarnings({"nullness:argument.type.incompatible", "nullness:return.type.incompatible"})
   public static <T> T[] nullSafeArrayCopy(T[] input, int length) {
     Assertions.checkArgument(length <= input.length);
     return Arrays.copyOf(input, length);
   }
 
   /**
+   * Creates a {@link Handler} with the specified {@link Handler.Callback} on the current {@link
+   * Looper} thread. The method accepts partially initialized objects as callback under the
+   * assumption that the Handler won't be used to send messages until the callback is fully
+   * initialized.
+   *
+   * @param callback A {@link Handler.Callback}. May be a partially initialized class.
+   * @return A {@link Handler} with the specified callback on the current {@link Looper} thread.
+   */
+  public static Handler createHandler(Handler.@UnknownInitialization Callback callback) {
+    return createHandler(Looper.myLooper(), callback);
+  }
+
+  /**
+   * Creates a {@link Handler} with the specified {@link Handler.Callback} on the specified {@link
+   * Looper} thread. The method accepts partially initialized objects as callback under the
+   * assumption that the Handler won't be used to send messages until the callback is fully
+   * initialized.
+   *
+   * @param looper A {@link Looper} to run the callback on.
+   * @param callback A {@link Handler.Callback}. May be a partially initialized class.
+   * @return A {@link Handler} with the specified callback on the current {@link Looper} thread.
+   */
+  @SuppressWarnings({"nullness:argument.type.incompatible", "nullness:return.type.incompatible"})
+  public static Handler createHandler(
+      Looper looper, Handler.@UnknownInitialization Callback callback) {
+    return new Handler(looper, callback);
+  }
+
+  /**
    * Instantiates a new single threaded executor whose thread has the specified name.
    *
    * @param threadName The name of the thread.

library/core/src/main/java/com/google/android/exoplayer2/video/VideoFrameReleaseTimeHelper.java

@@ -291,7 +291,7 @@ public final class VideoFrameReleaseTimeHelper {
       sampledVsyncTimeNs = C.TIME_UNSET;
       choreographerOwnerThread = new HandlerThread("ChoreographerOwner:Handler");
       choreographerOwnerThread.start();
-      handler = new Handler(choreographerOwnerThread.getLooper(), this);
+      handler = Util.createHandler(choreographerOwnerThread.getLooper(), /* callback= */ this);
       handler.sendEmptyMessage(CREATE_CHOREOGRAPHER);
     }
 

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/PlayerEmsgHandler.java

@@ -35,6 +35,7 @@ import com.google.android.exoplayer2.source.chunk.Chunk;
 import com.google.android.exoplayer2.source.dash.manifest.DashManifest;
 import com.google.android.exoplayer2.upstream.Allocator;
 import com.google.android.exoplayer2.util.ParsableByteArray;
+import com.google.android.exoplayer2.util.Util;
 import java.io.IOException;
 import java.util.Iterator;
 import java.util.Map;
@@ -100,7 +101,6 @@ public final class PlayerEmsgHandler implements Handler.Callback {
    *     messages that generate DASH media source events.
    * @param allocator An {@link Allocator} from which allocations can be obtained.
    */
-  @SuppressWarnings("nullness")
   public PlayerEmsgHandler(
       DashManifest manifest, PlayerEmsgCallback playerEmsgCallback, Allocator allocator) {
     this.manifest = manifest;
@@ -108,7 +108,7 @@ public final class PlayerEmsgHandler implements Handler.Callback {
     this.allocator = allocator;
 
     manifestPublishTimeToExpiryTimeUs = new TreeMap<>();
-    handler = new Handler(this);
+    handler = Util.createHandler(/* callback= */ this);
     decoder = new EventMessageDecoder();
     lastLoadedChunkEndTimeUs = C.TIME_UNSET;
     lastLoadedChunkEndTimeBeforeRefreshUs = C.TIME_UNSET;