Android Embedding Refactor PR34: Fill in missing nullability annotations. (#9384)

shell/platform/android/io/flutter/embedding/android/AndroidKeyProcessor.java

@@ -13,7 +13,9 @@ import io.flutter.embedding.engine.systemchannels.KeyEventChannel;
 import io.flutter.plugin.editing.TextInputPlugin;
 
 public class AndroidKeyProcessor {
+  @NonNull
   private final KeyEventChannel keyEventChannel;
+  @NonNull
   private final TextInputPlugin textInputPlugin;
   private int combiningCharacter;
 

shell/platform/android/io/flutter/embedding/android/AndroidTouchProcessor.java

@@ -89,7 +89,7 @@ public class AndroidTouchProcessor {
    * Sends the given {@link MotionEvent} data to Flutter in a format that
    * Flutter understands.
    */
-  public boolean onTouchEvent(MotionEvent event) {
+  public boolean onTouchEvent(@NonNull MotionEvent event) {
     int pointerCount = event.getPointerCount();
 
     // Prepare a data packet of the appropriate size and order.
@@ -145,7 +145,7 @@ public class AndroidTouchProcessor {
    * Generic motion events include joystick movement, mouse hover, track pad touches, scroll wheel
    * movements, etc.
    */
-  public boolean onGenericMotionEvent(MotionEvent event) {
+  public boolean onGenericMotionEvent(@NonNull MotionEvent event) {
     // Method isFromSource is only available in API 18+ (Jelly Bean MR2)
     // Mouse hover support is not implemented for API < 18.
     boolean isPointerEvent = Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2

shell/platform/android/io/flutter/embedding/android/FlutterActivity.java

@@ -87,16 +87,19 @@ public class FlutterActivity extends FragmentActivity implements OnFirstFrameRen
   private static final String TAG_FLUTTER_FRAGMENT = "flutter_fragment";
   // TODO(mattcarroll): replace ID with R.id when build system supports R.java
   private static final int FRAGMENT_CONTAINER_ID = 609893468; // random number
+  @Nullable
   private FlutterFragment flutterFragment;
 
   // Used to cover the Activity until the 1st frame is rendered so as to
   // avoid a brief black flicker from a SurfaceView version of FlutterView.
+  @Nullable
   private View coverView;
 
   /**
    * Creates an {@link Intent} that launches a {@code FlutterActivity}, which executes
    * a {@code main()} Dart entrypoint, and displays the "/" route as Flutter's initial route.
    */
+  @NonNull
   public static Intent createDefaultIntent(@NonNull Context launchContext) {
     return createBuilder().build(launchContext);
   }
@@ -105,6 +108,7 @@ public class FlutterActivity extends FragmentActivity implements OnFirstFrameRen
    * Creates an {@link IntentBuilder}, which can be used to configure an {@link Intent} to
    * launch a {@code FlutterActivity}.
    */
+  @NonNull
   public static IntentBuilder createBuilder() {
     return new IntentBuilder(FlutterActivity.class);
   }
@@ -178,7 +182,7 @@ public class FlutterActivity extends FragmentActivity implements OnFirstFrameRen
   }
 
   @Override
-  protected void onCreate(Bundle savedInstanceState) {
+  protected void onCreate(@Nullable Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     configureWindowForTransparency();
     setContentView(createFragmentContainer());
@@ -368,7 +372,7 @@ public class FlutterActivity extends FragmentActivity implements OnFirstFrameRen
   }
 
   @Override
-  protected void onNewIntent(Intent intent) {
+  protected void onNewIntent(@NonNull Intent intent) {
     // Forward Intents to our FlutterFragment in case it cares.
     flutterFragment.onNewIntent(intent);
   }

shell/platform/android/io/flutter/embedding/android/FlutterFragment.java

@@ -331,7 +331,7 @@ public class FlutterFragment extends Fragment {
   }
 
   @Override
-  public void onAttach(Context context) {
+  public void onAttach(@NonNull Context context) {
     super.onAttach(context);
 
     initializeFlutter(getContextCompat());
@@ -438,7 +438,7 @@ public class FlutterFragment extends Fragment {
 
   @Nullable
   @Override
-  public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
+  public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
     Log.v(TAG, "Creating FlutterView.");
     flutterView = new FlutterView(getContext(), getRenderMode(), getTransparencyMode());
     flutterView.addOnFirstFrameRenderedListener(onFirstFrameRenderedListener);

shell/platform/android/io/flutter/embedding/android/FlutterSurfaceView.java

@@ -50,7 +50,7 @@ public class FlutterSurfaceView extends SurfaceView implements FlutterRenderer.R
   // FlutterRenderer, and then on to the JNI bridge over to native Flutter code.
   private final SurfaceHolder.Callback surfaceCallback = new SurfaceHolder.Callback() {
     @Override
-    public void surfaceCreated(SurfaceHolder holder) {
+    public void surfaceCreated(@NonNull SurfaceHolder holder) {
       Log.v(TAG, "SurfaceHolder.Callback.surfaceCreated()");
       isSurfaceAvailableForRendering = true;
 
@@ -60,7 +60,7 @@ public class FlutterSurfaceView extends SurfaceView implements FlutterRenderer.R
     }
 
     @Override
-    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
+    public void surfaceChanged(@NonNull SurfaceHolder holder, int format, int width, int height) {
       Log.v(TAG, "SurfaceHolder.Callback.surfaceChanged()");
       if (isAttachedToFlutterRenderer) {
         changeSurfaceSize(width, height);
@@ -68,7 +68,7 @@ public class FlutterSurfaceView extends SurfaceView implements FlutterRenderer.R
     }
 
     @Override
-    public void surfaceDestroyed(SurfaceHolder holder) {
+    public void surfaceDestroyed(@NonNull SurfaceHolder holder) {
       Log.v(TAG, "SurfaceHolder.Callback.surfaceDestroyed()");
       isSurfaceAvailableForRendering = false;
 

shell/platform/android/io/flutter/embedding/android/FlutterTextureView.java

@@ -61,7 +61,7 @@ public class FlutterTextureView extends TextureView implements FlutterRenderer.R
     }
 
     @Override
-    public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
+    public void onSurfaceTextureSizeChanged(@NonNull SurfaceTexture surface, int width, int height) {
       Log.v(TAG, "SurfaceTextureListener.onSurfaceTextureSizeChanged()");
       if (isAttachedToFlutterRenderer) {
         changeSurfaceSize(width, height);
@@ -69,12 +69,12 @@ public class FlutterTextureView extends TextureView implements FlutterRenderer.R
     }
 
     @Override
-    public void onSurfaceTextureUpdated(SurfaceTexture surface) {
+    public void onSurfaceTextureUpdated(@NonNull SurfaceTexture surface) {
       // Invoked every time a new frame is available. We don't care.
     }
 
     @Override
-    public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
+    public boolean onSurfaceTextureDestroyed(@NonNull SurfaceTexture surface) {
       Log.v(TAG, "SurfaceTextureListener.onSurfaceTextureDestroyed()");
       isSurfaceAvailableForRendering = false;
 
@@ -93,14 +93,14 @@ public class FlutterTextureView extends TextureView implements FlutterRenderer.R
   /**
    * Constructs a {@code FlutterTextureView} programmatically, without any XML attributes.
    */
-  public FlutterTextureView(Context context) {
+  public FlutterTextureView(@NonNull Context context) {
     this(context, null);
   }
 
   /**
    * Constructs a {@code FlutterTextureView} in an XML-inflation-compliant manner.
    */
-  public FlutterTextureView(Context context, AttributeSet attrs) {
+  public FlutterTextureView(@NonNull Context context, @Nullable AttributeSet attrs) {
     super(context, attrs);
     init();
   }

shell/platform/android/io/flutter/embedding/android/FlutterView.java

@@ -238,7 +238,7 @@ public class FlutterView extends FrameLayout {
    * change, device language change, device text scale factor change, etc.
    */
   @Override
-  protected void onConfigurationChanged(Configuration newConfig) {
+  protected void onConfigurationChanged(@NonNull Configuration newConfig) {
     super.onConfigurationChanged(newConfig);
     Log.v(TAG, "Configuration changed. Sending locales and user settings to Flutter.");
     sendLocalesToFlutter(newConfig);
@@ -280,7 +280,8 @@ public class FlutterView extends FrameLayout {
   @Override
   @TargetApi(20)
   @RequiresApi(20)
-  public final WindowInsets onApplyWindowInsets(WindowInsets insets) {
+  @NonNull
+  public final WindowInsets onApplyWindowInsets(@NonNull WindowInsets insets) {
     WindowInsets newInsets = super.onApplyWindowInsets(insets);
 
     // Status bar (top) and left/right system insets should partially obscure the content (padding).
@@ -315,7 +316,7 @@ public class FlutterView extends FrameLayout {
    */
   @Override
   @SuppressWarnings("deprecation")
-  protected boolean fitSystemWindows(Rect insets) {
+  protected boolean fitSystemWindows(@NonNull Rect insets) {
     if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT) {
       // Status bar, left/right system insets partially obscure content (padding).
       viewportMetrics.paddingTop = insets.top;
@@ -358,7 +359,8 @@ public class FlutterView extends FrameLayout {
    * rather than spread that logic throughout this {@code FlutterView}.
    */
   @Override
-  public InputConnection onCreateInputConnection(EditorInfo outAttrs) {
+  @Nullable
+  public InputConnection onCreateInputConnection(@NonNull EditorInfo outAttrs) {
     if (!isAttachedToFlutterEngine()) {
       return super.onCreateInputConnection(outAttrs);
     }
@@ -380,7 +382,7 @@ public class FlutterView extends FrameLayout {
    * character.
    */
   @Override
-  public boolean onKeyUp(int keyCode, KeyEvent event) {
+  public boolean onKeyUp(int keyCode, @NonNull KeyEvent event) {
     if (!isAttachedToFlutterEngine()) {
       return super.onKeyUp(keyCode, event);
     }
@@ -403,7 +405,7 @@ public class FlutterView extends FrameLayout {
    * character.
    */
   @Override
-  public boolean onKeyDown(int keyCode, KeyEvent event) {
+  public boolean onKeyDown(int keyCode, @NonNull KeyEvent event) {
     if (!isAttachedToFlutterEngine()) {
       return super.onKeyDown(keyCode, event);
     }
@@ -419,7 +421,7 @@ public class FlutterView extends FrameLayout {
    * method forwards all {@link MotionEvent} data from Android to Flutter.
    */
   @Override
-  public boolean onTouchEvent(MotionEvent event) {
+  public boolean onTouchEvent(@NonNull MotionEvent event) {
     if (!isAttachedToFlutterEngine()) {
       return super.onTouchEvent(event);
     }
@@ -444,7 +446,7 @@ public class FlutterView extends FrameLayout {
    * method forwards all {@link MotionEvent} data from Android to Flutter.
    */
   @Override
-  public boolean onGenericMotionEvent(MotionEvent event) {
+  public boolean onGenericMotionEvent(@NonNull MotionEvent event) {
     boolean handled = isAttachedToFlutterEngine() && androidTouchProcessor.onGenericMotionEvent(event);
     return handled ? true : super.onGenericMotionEvent(event);
   }
@@ -461,7 +463,7 @@ public class FlutterView extends FrameLayout {
    * processed here for accessibility purposes.
    */
   @Override
-  public boolean onHoverEvent(MotionEvent event) {
+  public boolean onHoverEvent(@NonNull MotionEvent event) {
     if (!isAttachedToFlutterEngine()) {
       return super.onHoverEvent(event);
     }
@@ -477,6 +479,7 @@ public class FlutterView extends FrameLayout {
 
   //-------- Start: Accessibility -------
   @Override
+  @Nullable
   public AccessibilityNodeProvider getAccessibilityNodeProvider() {
     if (accessibilityBridge != null && accessibilityBridge.isAccessibilityEnabled()) {
       return accessibilityBridge;
@@ -661,7 +664,7 @@ public class FlutterView extends FrameLayout {
    * FlutterEngine must be non-null when this method is invoked.
    */
   @SuppressWarnings("deprecation")
-  private void sendLocalesToFlutter(Configuration config) {
+  private void sendLocalesToFlutter(@NonNull Configuration config) {
     List<Locale> locales = new ArrayList<>();
     if (Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {
       LocaleList localeList = config.getLocales();

shell/platform/android/io/flutter/embedding/engine/FlutterEngine.java

@@ -88,7 +88,9 @@ public class FlutterEngine implements LifecycleOwner {
   @NonNull
   private final TextInputChannel textInputChannel;
 
+  @NonNull
   private final Set<EngineLifecycleListener> engineLifecycleListeners = new HashSet<>();
+  @NonNull
   private final EngineLifecycleListener engineLifecycleListener = new EngineLifecycleListener() {
     @SuppressWarnings("unused")
     public void onPreEngineRestart() {

shell/platform/android/io/flutter/embedding/engine/FlutterEngineAndroidLifecycle.java

@@ -40,6 +40,7 @@ final class FlutterEngineAndroidLifecycle extends LifecycleRegistry {
   private Lifecycle backingLifecycle;
   private boolean isDestroyed = false;
 
+  @NonNull
   private final LifecycleObserver forwardingObserver = new DefaultLifecycleObserver() {
     @Override
     public void onCreate(@NonNull LifecycleOwner owner) {

shell/platform/android/io/flutter/embedding/engine/FlutterEnginePluginRegistry.java

@@ -43,31 +43,46 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
   private static final String TAG = "EnginePluginRegistry";
 
   // PluginRegistry
+  @NonNull
   private final Map<Class<? extends FlutterPlugin>, FlutterPlugin> plugins = new HashMap<>();
 
   // Standard FlutterPlugin
+  @NonNull
   private final FlutterPlugin.FlutterPluginBinding pluginBinding;
+  @NonNull
   private final FlutterEngineAndroidLifecycle flutterEngineAndroidLifecycle;
 
   // ActivityAware
+  @NonNull
   private final Map<Class<? extends FlutterPlugin>, ActivityAware> activityAwarePlugins = new HashMap<>();
+  @Nullable
   private Activity activity;
+  @Nullable
   private FlutterEngineActivityPluginBinding activityPluginBinding;
   private boolean isWaitingForActivityReattachment = false;
 
   // ServiceAware
+  @NonNull
   private final Map<Class<? extends FlutterPlugin>, ServiceAware> serviceAwarePlugins = new HashMap<>();
+  @Nullable
   private Service service;
+  @Nullable
   private FlutterEngineServicePluginBinding servicePluginBinding;
 
   // BroadcastReceiver
+  @NonNull
   private final Map<Class<? extends FlutterPlugin>, BroadcastReceiverAware> broadcastReceiverAwarePlugins = new HashMap<>();
+  @Nullable
   private BroadcastReceiver broadcastReceiver;
+  @Nullable
   private FlutterEngineBroadcastReceiverPluginBinding broadcastReceiverPluginBinding;
 
   // ContentProvider
+  @NonNull
   private final Map<Class<? extends FlutterPlugin>, ContentProviderAware> contentProviderAwarePlugins = new HashMap<>();
+  @Nullable
   private ContentProvider contentProvider;
+  @Nullable
   private FlutterEngineContentProviderPluginBinding contentProviderPluginBinding;
 
   FlutterEnginePluginRegistry(
@@ -329,7 +344,7 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
   }
 
   @Override
-  public boolean onActivityResult(int requestCode, int resultCode, @NonNull Intent data) {
+  public boolean onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
     Log.v(TAG, "Forwarding onActivityResult() to plugins.");
     if (isAttachedToActivity()) {
       return activityPluginBinding.onActivityResult(requestCode, resultCode, data);
@@ -486,10 +501,15 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
   //----- End ContentProviderControlSurface -----
 
   private static class FlutterEngineActivityPluginBinding implements ActivityPluginBinding {
+    @NonNull
     private final Activity activity;
+    @NonNull
     private final Set<io.flutter.plugin.common.PluginRegistry.RequestPermissionsResultListener> onRequestPermissionsResultListeners = new HashSet<>();
+    @NonNull
     private final Set<io.flutter.plugin.common.PluginRegistry.ActivityResultListener> onActivityResultListeners = new HashSet<>();
+    @NonNull
     private final Set<io.flutter.plugin.common.PluginRegistry.NewIntentListener> onNewIntentListeners = new HashSet<>();
+    @NonNull
     private final Set<io.flutter.plugin.common.PluginRegistry.UserLeaveHintListener> onUserLeaveHintListeners = new HashSet<>();
 
     public FlutterEngineActivityPluginBinding(@NonNull Activity activity) {
@@ -556,7 +576,7 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
      * Invoked by the {@link FlutterEngine} that owns this {@code ActivityPluginBinding} when its
      * associated {@link Activity} has its {@code onActivityResult(...)} method invoked.
      */
-    boolean onActivityResult(int requestCode, int resultCode, @NonNull Intent data) {
+    boolean onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
       boolean didConsumeResult = false;
       for (io.flutter.plugin.common.PluginRegistry.ActivityResultListener listener : onActivityResultListeners) {
         didConsumeResult = listener.onActivityResult(requestCode, resultCode, data) || didConsumeResult;
@@ -620,15 +640,17 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
   }
 
   private static class FlutterEngineServicePluginBinding implements ServicePluginBinding {
+    @NonNull
     private final Service service;
+    @NonNull
     private final Set<ServiceAware.OnModeChangeListener> onModeChangeListeners = new HashSet<>();
 
     FlutterEngineServicePluginBinding(@NonNull Service service) {
       this.service = service;
     }
 
-    @NonNull
     @Override
+    @NonNull
     public Service getService() {
       return service;
     }
@@ -657,6 +679,7 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
   }
 
   private static class FlutterEngineBroadcastReceiverPluginBinding implements BroadcastReceiverPluginBinding {
+    @NonNull
     private final BroadcastReceiver broadcastReceiver;
 
     FlutterEngineBroadcastReceiverPluginBinding(@NonNull BroadcastReceiver broadcastReceiver) {
@@ -671,6 +694,7 @@ class FlutterEnginePluginRegistry implements PluginRegistry,
   }
 
   private static class FlutterEngineContentProviderPluginBinding implements ContentProviderPluginBinding {
+    @NonNull
     private final ContentProvider contentProvider;
 
     FlutterEngineContentProviderPluginBinding(@NonNull ContentProvider contentProvider) {

shell/platform/android/io/flutter/embedding/engine/FlutterJNI.java

@@ -94,21 +94,30 @@ public class FlutterJNI {
   private static final String TAG = "FlutterJNI";
 
   // This is set from native code via JNI.
+  @Nullable
   private static String observatoryUri;
 
   @UiThread
   public static native boolean nativeGetIsSoftwareRenderingEnabled();
 
+  @Nullable
   public static String getObservatoryUri() {
     return observatoryUri;
   }
 
+  @Nullable
   private Long nativePlatformViewId;
+  @Nullable
   private FlutterRenderer.RenderSurface renderSurface;
+  @Nullable
   private AccessibilityDelegate accessibilityDelegate;
+  @Nullable
   private PlatformMessageHandler platformMessageHandler;
+  @NonNull
   private final Set<EngineLifecycleListener> engineLifecycleListeners = new HashSet<>();
+  @NonNull
   private final Set<OnFirstFrameRenderedListener> firstFrameListeners = new HashSet<>();
+  @NonNull
   private final Looper mainLooper; // cached to avoid synchronization on repeat access.
 
   public FlutterJNI() {
@@ -139,7 +148,7 @@ public class FlutterJNI {
     nativePlatformViewId = nativeAttach(this, isBackgroundView);
   }
 
-  private native long nativeAttach(FlutterJNI flutterJNI, boolean isBackgroundView);
+  private native long nativeAttach(@NonNull FlutterJNI flutterJNI, boolean isBackgroundView);
 
   /**
    * Detaches this {@code FlutterJNI} instance from Flutter's native engine, which precludes
@@ -246,7 +255,7 @@ public class FlutterJNI {
     nativeSurfaceCreated(nativePlatformViewId, surface);
   }
 
-  private native void nativeSurfaceCreated(long nativePlatformViewId, Surface surface);
+  private native void nativeSurfaceCreated(long nativePlatformViewId, @NonNull Surface surface);
 
   /**
    * Call this method when the {@link Surface} changes that was previously registered with
@@ -341,14 +350,14 @@ public class FlutterJNI {
    * Sends a packet of pointer data to Flutter's engine.
    */
   @UiThread
-  public void dispatchPointerDataPacket(ByteBuffer buffer, int position) {
+  public void dispatchPointerDataPacket(@NonNull ByteBuffer buffer, int position) {
     ensureRunningOnMainThread();
     ensureAttachedToNative();
     nativeDispatchPointerDataPacket(nativePlatformViewId, buffer, position);
   }
 
   private native void nativeDispatchPointerDataPacket(long nativePlatformViewId,
-                                                      ByteBuffer buffer,
+                                                      @NonNull ByteBuffer buffer,
                                                       int position);
   //------ End Touch Interaction Support ---
 
@@ -377,7 +386,7 @@ public class FlutterJNI {
    */
   @SuppressWarnings("unused")
   @UiThread
-  private void updateSemantics(ByteBuffer buffer, String[] strings) {
+  private void updateSemantics(@NonNull ByteBuffer buffer, @NonNull String[] strings) {
     ensureRunningOnMainThread();
     if (accessibilityDelegate != null) {
       accessibilityDelegate.updateSemantics(buffer, strings);
@@ -395,7 +404,7 @@ public class FlutterJNI {
    */
   @SuppressWarnings("unused")
   @UiThread
-  private void updateCustomAccessibilityActions(ByteBuffer buffer, String[] strings) {
+  private void updateCustomAccessibilityActions(@NonNull ByteBuffer buffer, @NonNull String[] strings) {
     ensureRunningOnMainThread();
     if (accessibilityDelegate != null) {
       accessibilityDelegate.updateCustomAccessibilityActions(buffer, strings);
@@ -434,7 +443,7 @@ public class FlutterJNI {
    * {@link #dispatchSemanticsAction(int, AccessibilityBridge.Action, Object)}.
    */
   @UiThread
-  public void dispatchSemanticsAction(int id, int action, ByteBuffer args, int argsPosition) {
+  public void dispatchSemanticsAction(int id, int action, @Nullable ByteBuffer args, int argsPosition) {
     ensureRunningOnMainThread();
     ensureAttachedToNative();
     nativeDispatchSemanticsAction(nativePlatformViewId, id, action, args, argsPosition);
@@ -444,7 +453,7 @@ public class FlutterJNI {
       long nativePlatformViewId,
       int id,
       int action,
-      ByteBuffer args,
+      @Nullable ByteBuffer args,
       int argsPosition
   );
 
@@ -478,13 +487,13 @@ public class FlutterJNI {
    * texture within Flutter's UI.
    */
   @UiThread
-  public void registerTexture(long textureId, SurfaceTexture surfaceTexture) {
+  public void registerTexture(long textureId, @NonNull SurfaceTexture surfaceTexture) {
     ensureRunningOnMainThread();
     ensureAttachedToNative();
     nativeRegisterTexture(nativePlatformViewId, textureId, surfaceTexture);
   }
 
-  private native void nativeRegisterTexture(long nativePlatformViewId, long textureId, SurfaceTexture surfaceTexture);
+  private native void nativeRegisterTexture(long nativePlatformViewId, long textureId, @NonNull SurfaceTexture surfaceTexture);
 
   /**
    * Call this method to inform Flutter that a texture previously registered with
@@ -580,8 +589,9 @@ public class FlutterJNI {
   }
 
   // Called by native.
+  // TODO(mattcarroll): determine if message is nonull or nullable
   @SuppressWarnings("unused")
-  private void handlePlatformMessage(final String channel, byte[] message, final int replyId) {
+  private void handlePlatformMessage(@NonNull final String channel, byte[] message, final int replyId) {
     if (platformMessageHandler != null) {
       platformMessageHandler.handleMessageFromDart(channel, message, replyId);
     }
@@ -589,6 +599,7 @@ public class FlutterJNI {
   }
 
   // Called by native to respond to a platform message that we sent.
+  // TODO(mattcarroll): determine if reply is nonull or nullable
   @SuppressWarnings("unused")
   private void handlePlatformMessageResponse(int replyId, byte[] reply) {
     if (platformMessageHandler != null) {
@@ -602,7 +613,7 @@ public class FlutterJNI {
    * {@code channel}.
    */
   @UiThread
-  public void dispatchEmptyPlatformMessage(String channel, int responseId) {
+  public void dispatchEmptyPlatformMessage(@NonNull String channel, int responseId) {
     ensureRunningOnMainThread();
     if (isAttached()) {
       nativeDispatchEmptyPlatformMessage(nativePlatformViewId, channel, responseId);
@@ -614,7 +625,7 @@ public class FlutterJNI {
   // Send an empty platform message to Dart.
   private native void nativeDispatchEmptyPlatformMessage(
       long nativePlatformViewId,
-      String channel,
+      @NonNull String channel,
       int responseId
   );
 
@@ -622,7 +633,7 @@ public class FlutterJNI {
    * Sends a reply {@code message} from Android to Flutter over the given {@code channel}.
    */
   @UiThread
-  public void dispatchPlatformMessage(String channel, ByteBuffer message, int position, int responseId) {
+  public void dispatchPlatformMessage(@NonNull String channel, @Nullable ByteBuffer message, int position, int responseId) {
     ensureRunningOnMainThread();
     if (isAttached()) {
       nativeDispatchPlatformMessage(
@@ -640,8 +651,8 @@ public class FlutterJNI {
   // Send a data-carrying platform message to Dart.
   private native void nativeDispatchPlatformMessage(
       long nativePlatformViewId,
-      String channel,
-      ByteBuffer message,
+      @NonNull String channel,
+      @Nullable ByteBuffer message,
       int position,
       int responseId
   );
@@ -665,7 +676,7 @@ public class FlutterJNI {
 
   // TODO(mattcarroll): differentiate between channel responses and platform responses.
   @UiThread
-  public void invokePlatformMessageResponseCallback(int responseId, ByteBuffer message, int position) {
+  public void invokePlatformMessageResponseCallback(int responseId, @Nullable ByteBuffer message, int position) {
     ensureRunningOnMainThread();
     if (isAttached()) {
       nativeInvokePlatformMessageResponseCallback(
@@ -683,7 +694,7 @@ public class FlutterJNI {
   private native void nativeInvokePlatformMessageResponseCallback(
       long nativePlatformViewId,
       int responseId,
-      ByteBuffer message,
+      @Nullable ByteBuffer message,
       int position
   );
   //------- End Platform Message Support ----
@@ -718,6 +729,7 @@ public class FlutterJNI {
   }
   //----- End Engine Lifecycle Support ----
 
+  // TODO(mattcarroll): determine if this is nonull or nullable
   @UiThread
   public Bitmap getBitmap() {
     ensureRunningOnMainThread();
@@ -725,6 +737,7 @@ public class FlutterJNI {
     return nativeGetBitmap(nativePlatformViewId);
   }
 
+  // TODO(mattcarroll): determine if this is nonull or nullable
   private native Bitmap nativeGetBitmap(long nativePlatformViewId);
 
   private void ensureRunningOnMainThread() {
@@ -749,7 +762,7 @@ public class FlutterJNI {
      * Implementers are expected to maintain an Android-side cache of custom accessibility actions.
      * This method provides new actions to add to that cache.
      */
-    void updateCustomAccessibilityActions(ByteBuffer buffer, String[] strings);
+    void updateCustomAccessibilityActions(@NonNull ByteBuffer buffer, @NonNull String[] strings);
 
     /**
      * Sends new {@code SemanticsNode} information from Flutter to Android.
@@ -757,6 +770,6 @@ public class FlutterJNI {
      * Implementers are expected to maintain an Android-side cache of Flutter's semantics tree.
      * This method provides updates from Flutter for the Android-side semantics tree cache.
      */
-    void updateSemantics(ByteBuffer buffer, String[] strings);
+    void updateSemantics(@NonNull ByteBuffer buffer, @NonNull String[] strings);
   }
 }

shell/platform/android/io/flutter/embedding/engine/FlutterShellArgs.java

@@ -92,6 +92,7 @@ public class FlutterShellArgs {
     return new FlutterShellArgs(args);
   }
 
+  @NonNull
   private Set<String> args;
 
   /**

shell/platform/android/io/flutter/embedding/engine/dart/DartExecutor.java

@@ -45,7 +45,9 @@ public class DartExecutor implements BinaryMessenger {
   @NonNull
   private final DartMessenger messenger;
   private boolean isApplicationRunning = false;
+  @Nullable
   private String isolateServiceId;
+  @Nullable
   private IsolateServiceIdListener isolateServiceIdListener;
 
   private final BinaryMessenger.BinaryMessageHandler isolateChannelMessageHandler =
@@ -206,6 +208,7 @@ public class DartExecutor implements BinaryMessenger {
    * Returns an identifier for this executor's primary isolate.  This identifier can be used
    * in queries to the Dart service protocol.
    */
+  @Nullable
   public String getIsolateServiceId() {
     return isolateServiceId;
   }
@@ -214,14 +217,14 @@ public class DartExecutor implements BinaryMessenger {
    * Callback interface invoked when the isolate identifier becomes available.
    */
   interface IsolateServiceIdListener {
-    void onIsolateServiceIdAvailable(String isolateServiceId);
+    void onIsolateServiceIdAvailable(@NonNull String isolateServiceId);
   }
 
   /**
    * Set a listener that will be notified when an isolate identifier is available for this
    * executor's primary isolate.
    */
-  public void setIsolateServiceIdListener(IsolateServiceIdListener listener) {
+  public void setIsolateServiceIdListener(@Nullable IsolateServiceIdListener listener) {
     isolateServiceIdListener = listener;
     if (isolateServiceIdListener != null && isolateServiceId != null) {
       isolateServiceIdListener.onIsolateServiceIdAvailable(isolateServiceId);

shell/platform/android/io/flutter/embedding/engine/dart/DartMessenger.java

@@ -130,7 +130,7 @@ class DartMessenger implements BinaryMessenger, PlatformMessageHandler {
     }
 
     @Override
-    public void reply(ByteBuffer reply) {
+    public void reply(@Nullable ByteBuffer reply) {
       if (done.getAndSet(true)) {
         throw new IllegalStateException("Reply already submitted");
       }

shell/platform/android/io/flutter/embedding/engine/dart/PlatformMessageHandler.java

@@ -4,12 +4,15 @@
 
 package io.flutter.embedding.engine.dart;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+
 /**
  * WARNING: THIS CLASS IS EXPERIMENTAL. DO NOT SHIP A DEPENDENCY ON THIS CODE.
  * IF YOU USE IT, WE WILL BREAK YOU.
  */
 public interface PlatformMessageHandler {
-  void handleMessageFromDart(final String channel, byte[] message, final int replyId);
+  void handleMessageFromDart(@NonNull final String channel, @Nullable byte[] message, final int replyId);
 
-  void handlePlatformMessageResponse(int replyId, byte[] reply);
+  void handlePlatformMessageResponse(int replyId, @Nullable byte[] reply);
 }

shell/platform/android/io/flutter/embedding/engine/plugins/activity/ActivityControlSurface.java

@@ -8,6 +8,7 @@ import android.app.Activity;
 import android.arch.lifecycle.Lifecycle;
 import android.content.Intent;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 /**
  * Control surface through which an {@link Activity} attaches to a {@link FlutterEngine}.
@@ -82,7 +83,7 @@ public interface ActivityControlSurface {
    * <p>
    * Returns true if one or more plugins utilized this {@link Activity} result.
    */
-  boolean onActivityResult(int requestCode, int resultCode, Intent data);
+  boolean onActivityResult(int requestCode, int resultCode, @Nullable Intent data);
 
   /**
    * Call this method from the {@link Activity} that is attached to this {@code ActivityControlSurface}'s

shell/platform/android/io/flutter/embedding/engine/renderer/FlutterRenderer.java

@@ -105,10 +105,11 @@ public class FlutterRenderer implements TextureRegistry {
 
   final class SurfaceTextureRegistryEntry implements TextureRegistry.SurfaceTextureEntry {
     private final long id;
+    @NonNull
     private final SurfaceTexture surfaceTexture;
     private boolean released;
 
-    SurfaceTextureRegistryEntry(long id, SurfaceTexture surfaceTexture) {
+    SurfaceTextureRegistryEntry(long id, @NonNull SurfaceTexture surfaceTexture) {
       this.id = id;
       this.surfaceTexture = surfaceTexture;
 
@@ -127,7 +128,7 @@ public class FlutterRenderer implements TextureRegistry {
 
     private SurfaceTexture.OnFrameAvailableListener onFrameListener = new SurfaceTexture.OnFrameAvailableListener() {
       @Override
-      public void onFrameAvailable(SurfaceTexture texture) {
+      public void onFrameAvailable(@NonNull SurfaceTexture texture) {
         if (released) {
           // Even though we make sure to unregister the callback before releasing, as of Android O
           // SurfaceTexture has a data race when accessing the callback, so the callback may
@@ -139,6 +140,7 @@ public class FlutterRenderer implements TextureRegistry {
     };
 
     @Override
+    @NonNull
     public SurfaceTexture surfaceTexture() {
       return surfaceTexture;
     }
@@ -162,7 +164,7 @@ public class FlutterRenderer implements TextureRegistry {
   //------ END TextureRegistry IMPLEMENTATION ----
 
   // TODO(mattcarroll): describe the native behavior that this invokes
-  public void surfaceCreated(Surface surface) {
+  public void surfaceCreated(@NonNull Surface surface) {
     flutterJNI.onSurfaceCreated(surface);
   }
 
@@ -201,17 +203,18 @@ public class FlutterRenderer implements TextureRegistry {
   }
 
   // TODO(mattcarroll): describe the native behavior that this invokes
+  // TODO(mattcarroll): determine if this is nullable or nonnull
   public Bitmap getBitmap() {
     return flutterJNI.getBitmap();
   }
 
   // TODO(mattcarroll): describe the native behavior that this invokes
-  public void dispatchPointerDataPacket(ByteBuffer buffer, int position) {
+  public void dispatchPointerDataPacket(@NonNull ByteBuffer buffer, int position) {
     flutterJNI.dispatchPointerDataPacket(buffer, position);
   }
 
   // TODO(mattcarroll): describe the native behavior that this invokes
-  private void registerTexture(long textureId, SurfaceTexture surfaceTexture) {
+  private void registerTexture(long textureId, @NonNull SurfaceTexture surfaceTexture) {
     flutterJNI.registerTexture(textureId, surfaceTexture);
   }
 
@@ -243,7 +246,7 @@ public class FlutterRenderer implements TextureRegistry {
   // TODO(mattcarroll): describe the native behavior that this invokes
   public void dispatchSemanticsAction(int id,
                                       int action,
-                                      ByteBuffer args,
+                                      @Nullable ByteBuffer args,
                                       int argsPosition) {
     flutterJNI.dispatchSemanticsAction(
         id,

shell/platform/android/io/flutter/embedding/engine/systemchannels/AccessibilityChannel.java

@@ -30,7 +30,7 @@ public class AccessibilityChannel {
 
   private final BasicMessageChannel.MessageHandler<Object> parsingMessageHandler = new BasicMessageChannel.MessageHandler<Object>() {
     @Override
-    public void onMessage(Object message, BasicMessageChannel.Reply<Object> reply) {
+    public void onMessage(@Nullable Object message, @NonNull BasicMessageChannel.Reply<Object> reply) {
       // If there is no handler to respond to this message then we don't need to
       // parse it. Return.
       if (handler == null) {

shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java

@@ -32,7 +32,7 @@ public class LocalizationChannel {
   /**
    * Send the given {@code locales} to Dart.
    */
-  public void sendLocales(List<Locale> locales) {
+  public void sendLocales(@NonNull List<Locale> locales) {
     Log.v(TAG, "Sending Locales to Flutter.");
     List<String> data = new ArrayList<>();
     for (Locale locale : locales) {

shell/platform/android/io/flutter/embedding/engine/systemchannels/NavigationChannel.java

@@ -25,12 +25,12 @@ public class NavigationChannel {
     this.channel = new MethodChannel(dartExecutor, "flutter/navigation", JSONMethodCodec.INSTANCE);
   }
 
-  public void setInitialRoute(String initialRoute) {
+  public void setInitialRoute(@NonNull String initialRoute) {
     Log.v(TAG, "Sending message to set initial route to '" + initialRoute + "'");
     channel.invokeMethod("setInitialRoute", initialRoute);
   }
 
-  public void pushRoute(String route) {
+  public void pushRoute(@NonNull String route) {
     Log.v(TAG, "Sending message to push route '" + route + "'");
     channel.invokeMethod("pushRoute", route);
   }

shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformChannel.java

@@ -35,7 +35,7 @@ public class PlatformChannel {
 
   private final MethodChannel.MethodCallHandler parsingMethodCallHandler = new MethodChannel.MethodCallHandler() {
     @Override
-    public void onMethodCall(MethodCall call, MethodChannel.Result result) {
+    public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
       if (platformMessageHandler == null) {
         // If no explicit PlatformMessageHandler has been registered then we don't
         // need to forward this call to an API. Return.
@@ -257,6 +257,7 @@ public class PlatformChannel {
     return ActivityInfo.SCREEN_ORIENTATION_PORTRAIT;
   }
 
+  @NonNull
   private AppSwitcherDescription decodeAppSwitcherDescription(@NonNull JSONObject encodedDescription) throws JSONException {
     int color = encodedDescription.getInt("primaryColor");
     if (color != 0) { // 0 means color isn't set, use system default
@@ -272,6 +273,7 @@ public class PlatformChannel {
    * @throws JSONException if {@code encodedSystemUiOverlay} does not contain expected keys and value types.
    * @throws NoSuchFieldException if any of the given encoded overlay names are invalid.
    */
+  @NonNull
   private List<SystemUiOverlay> decodeSystemUiOverlays(@NonNull JSONArray encodedSystemUiOverlay) throws JSONException, NoSuchFieldException {
     List<SystemUiOverlay> overlays = new ArrayList<>();
     for (int i = 0; i < encodedSystemUiOverlay.length(); ++i) {
@@ -295,6 +297,7 @@ public class PlatformChannel {
    * @throws JSONException if {@code encodedStyle} does not contain expected keys and value types.
    * @throws NoSuchFieldException if any provided brightness name is invalid.
    */
+  @NonNull
   private SystemChromeStyle decodeSystemChromeStyle(@NonNull JSONObject encodedStyle) throws JSONException, NoSuchFieldException {
     Brightness systemNavigationBarIconBrightness = null;
     // TODO(mattcarroll): add color annotation
@@ -425,6 +428,7 @@ public class PlatformChannel {
   public enum SoundType {
     CLICK("SystemSoundType.click");
 
+    @NonNull
     static SoundType fromValue(@NonNull String encodedName) throws NoSuchFieldException {
       for (SoundType soundType : SoundType.values()) {
         if (soundType.encodedName.equals(encodedName)) {
@@ -453,6 +457,7 @@ public class PlatformChannel {
     HEAVY_IMPACT("HapticFeedbackType.heavyImpact"),
     SELECTION_CLICK("HapticFeedbackType.selectionClick");
 
+    @NonNull
     static HapticFeedbackType fromValue(@Nullable String encodedName) throws NoSuchFieldException {
       for (HapticFeedbackType feedbackType : HapticFeedbackType.values()) {
         if ((feedbackType.encodedName == null && encodedName == null)
@@ -480,6 +485,7 @@ public class PlatformChannel {
     LANDSCAPE_LEFT("DeviceOrientation.landscapeLeft"),
     LANDSCAPE_RIGHT("DeviceOrientation.landscapeRight");
 
+    @NonNull
     static DeviceOrientation fromValue(@NonNull String encodedName) throws NoSuchFieldException {
       for (DeviceOrientation orientation : DeviceOrientation.values()) {
         if (orientation.encodedName.equals(encodedName)) {
@@ -508,6 +514,7 @@ public class PlatformChannel {
     TOP_OVERLAYS("SystemUiOverlay.top"),
     BOTTOM_OVERLAYS("SystemUiOverlay.bottom");
 
+    @NonNull
     static SystemUiOverlay fromValue(@NonNull String encodedName) throws NoSuchFieldException {
       for (SystemUiOverlay overlay : SystemUiOverlay.values()) {
         if (overlay.encodedName.equals(encodedName)) {
@@ -578,6 +585,7 @@ public class PlatformChannel {
     LIGHT("Brightness.light"),
     DARK("Brightness.dark");
 
+    @NonNull
     static Brightness fromValue(@NonNull String encodedName) throws NoSuchFieldException {
       for (Brightness brightness : Brightness.values()) {
         if (brightness.encodedName.equals(encodedName)) {
@@ -601,7 +609,8 @@ public class PlatformChannel {
   public enum ClipboardContentFormat {
     PLAIN_TEXT("text/plain");
 
-    static ClipboardContentFormat fromValue(String encodedName) throws NoSuchFieldException {
+    @NonNull
+    static ClipboardContentFormat fromValue(@NonNull String encodedName) throws NoSuchFieldException {
       for (ClipboardContentFormat format : ClipboardContentFormat.values()) {
         if (format.encodedName.equals(encodedName)) {
           return format;

shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformViewsChannel.java

@@ -38,7 +38,7 @@ public class PlatformViewsChannel {
 
   private final MethodChannel.MethodCallHandler parsingHandler = new MethodChannel.MethodCallHandler() {
     @Override
-    public void onMethodCall(MethodCall call, MethodChannel.Result result) {
+    public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
       // If there is no handler to respond to this message then we don't need to
       // parse it. Return.
       if (handler == null) {
@@ -70,7 +70,7 @@ public class PlatformViewsChannel {
       }
     }
 
-    private void create(MethodCall call, MethodChannel.Result result) {
+    private void create(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
       Map<String, Object> createArgs = call.arguments();
       PlatformViewCreationRequest request = new PlatformViewCreationRequest(
           (int) createArgs.get("id"),
@@ -187,7 +187,7 @@ public class PlatformViewsChannel {
       }
     }
 
-    private void clearFocus(MethodCall call, MethodChannel.Result result) {
+    private void clearFocus(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
       int viewId = call.arguments();
       try {
         handler.clearFocus(viewId);

shell/platform/android/io/flutter/embedding/engine/systemchannels/SettingsChannel.java

@@ -17,35 +17,42 @@ public class SettingsChannel {
   private static final String TEXT_SCALE_FACTOR = "textScaleFactor";
   private static final String ALWAYS_USE_24_HOUR_FORMAT = "alwaysUse24HourFormat";
   private static final String PLATFORM_BRIGHTNESS = "platformBrightness";
-  
+
+  @NonNull
   public final BasicMessageChannel<Object> channel;
   
   public SettingsChannel(@NonNull DartExecutor dartExecutor) {
     this.channel = new BasicMessageChannel<>(dartExecutor, CHANNEL_NAME, JSONMessageCodec.INSTANCE);
   }
-  
+
+  @NonNull
   public MessageBuilder startMessage() {
     return new MessageBuilder(channel);
   }
   
   public static class MessageBuilder {
+    @NonNull
     private final BasicMessageChannel<Object> channel;
+    @NonNull
     private Map<String, Object> message = new HashMap<>();
     
     MessageBuilder(@NonNull BasicMessageChannel<Object> channel) {
       this.channel = channel;
     }
-    
+
+    @NonNull
     public MessageBuilder setTextScaleFactor(float textScaleFactor) {
       message.put(TEXT_SCALE_FACTOR, textScaleFactor);
       return this;
     }
-    
+
+    @NonNull
     public MessageBuilder setUse24HourFormat(boolean use24HourFormat) {
       message.put(ALWAYS_USE_24_HOUR_FORMAT, use24HourFormat);
       return this;
     }
-    
+
+    @NonNull
     public MessageBuilder setPlatformBrightness(@NonNull PlatformBrightness brightness) {
       message.put(PLATFORM_BRIGHTNESS, brightness.name);
       return this;
@@ -69,7 +76,8 @@ public class SettingsChannel {
   public enum PlatformBrightness {
     light("light"),
     dark("dark");
-    
+
+    @NonNull
     public String name;
     
     PlatformBrightness(@NonNull String name) {

shell/platform/android/io/flutter/embedding/engine/systemchannels/TextInputChannel.java

@@ -41,7 +41,7 @@ public class TextInputChannel {
 
   private final MethodChannel.MethodCallHandler parsingMethodHandler = new MethodChannel.MethodCallHandler() {
     @Override
-    public void onMethodCall(MethodCall call, MethodChannel.Result result) {
+    public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
       if (textInputMethodHandler == null) {
         // If no explicit TextInputMethodHandler has been registered then we don't
         // need to forward this call to an API. Return.
@@ -278,6 +278,7 @@ public class TextInputChannel {
       );
     }
 
+    @NonNull
     private static Integer inputActionFromTextInputAction(@NonNull String inputAction) {
       switch (inputAction) {
         case "TextInputAction.newline":

shell/platform/android/io/flutter/plugin/common/BasicMessageChannel.java

@@ -4,6 +4,8 @@
 
 package io.flutter.plugin.common;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.annotation.UiThread;
 import android.util.Log;
 import java.nio.ByteBuffer;
@@ -28,8 +30,11 @@ import io.flutter.plugin.common.BinaryMessenger.BinaryMessageHandler;
 public final class BasicMessageChannel<T> {
     private static final String TAG = "BasicMessageChannel#";
 
+    @NonNull
     private final BinaryMessenger messenger;
+    @NonNull
     private final String name;
+    @NonNull
     private final MessageCodec<T> codec;
 
     /**
@@ -40,7 +45,7 @@ public final class BasicMessageChannel<T> {
      * @param name a channel name String.
      * @param codec a {@link MessageCodec}.
      */
-    public BasicMessageChannel(BinaryMessenger messenger, String name, MessageCodec<T> codec) {
+    public BasicMessageChannel(@NonNull BinaryMessenger messenger, @NonNull String name, @NonNull MessageCodec<T> codec) {
         if (BuildConfig.DEBUG) {
             if (messenger == null) {
                 Log.e(TAG, "Parameter messenger must not be null.");
@@ -62,7 +67,7 @@ public final class BasicMessageChannel<T> {
      *
      * @param message the message, possibly null.
      */
-    public void send(T message) {
+    public void send(@Nullable T message) {
         send(message, null);
     }
 
@@ -75,7 +80,7 @@ public final class BasicMessageChannel<T> {
      * @param callback a {@link Reply} callback, possibly null.
      */
     @UiThread
-    public void send(T message, final Reply<T> callback) {
+    public void send(@Nullable T message, @Nullable final Reply<T> callback) {
         messenger.send(name, codec.encodeMessage(message),
             callback == null ? null : new IncomingReplyHandler(callback));
     }
@@ -92,7 +97,7 @@ public final class BasicMessageChannel<T> {
      * @param handler a {@link MessageHandler}, or null to deregister.
      */
     @UiThread
-    public void setMessageHandler(final MessageHandler<T> handler) {
+    public void setMessageHandler(@Nullable final MessageHandler<T> handler) {
         messenger.setMessageHandler(name,
             handler == null ? null : new IncomingMessageHandler(handler));
     }
@@ -119,7 +124,7 @@ public final class BasicMessageChannel<T> {
          * @param message the message, possibly null.
          * @param reply a {@link Reply} for sending a single message reply back to Flutter.
          */
-        void onMessage(T message, Reply<T> reply);
+        void onMessage(@Nullable T message, @NonNull Reply<T> reply);
     }
 
     /**
@@ -133,18 +138,18 @@ public final class BasicMessageChannel<T> {
          *
          * @param reply the reply, possibly null.
          */
-        void reply(T reply);
+        void reply(@Nullable T reply);
     }
 
     private final class IncomingReplyHandler implements BinaryReply {
         private final Reply<T> callback;
 
-        private IncomingReplyHandler(Reply<T> callback) {
+        private IncomingReplyHandler(@NonNull Reply<T> callback) {
             this.callback = callback;
         }
 
         @Override
-        public void reply(ByteBuffer reply) {
+        public void reply(@Nullable ByteBuffer reply) {
             try {
                 callback.reply(codec.decodeMessage(reply));
             } catch (RuntimeException e) {
@@ -156,12 +161,12 @@ public final class BasicMessageChannel<T> {
     private final class IncomingMessageHandler implements BinaryMessageHandler {
         private final MessageHandler<T> handler;
 
-        private IncomingMessageHandler(MessageHandler<T> handler) {
+        private IncomingMessageHandler(@NonNull MessageHandler<T> handler) {
             this.handler = handler;
         }
 
         @Override
-        public void onMessage(ByteBuffer message, final BinaryReply callback) {
+        public void onMessage(@Nullable ByteBuffer message, @NonNull final BinaryReply callback) {
             try {
                 handler.onMessage(codec.decodeMessage(message), new Reply<T>() {
                     @Override

shell/platform/android/io/flutter/plugin/common/BinaryMessenger.java

@@ -4,6 +4,8 @@
 
 package io.flutter.plugin.common;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.annotation.UiThread;
 
 import java.nio.ByteBuffer;
@@ -32,7 +34,7 @@ public interface BinaryMessenger {
      * between position zero and current position, or null.
      */
     @UiThread
-    void send(String channel, ByteBuffer message);
+    void send(@NonNull String channel, @Nullable ByteBuffer message);
 
     /**
      * Sends a binary message to the Flutter application, optionally expecting a reply.
@@ -46,7 +48,7 @@ public interface BinaryMessenger {
      * message, possibly null.
      */
     @UiThread
-    void send(String channel, ByteBuffer message, BinaryReply callback);
+    void send(@NonNull String channel, @Nullable ByteBuffer message, @Nullable BinaryReply callback);
 
     /**
      * Registers a handler to be invoked when the Flutter application sends a message
@@ -62,7 +64,7 @@ public interface BinaryMessenger {
      * @param handler a {@link BinaryMessageHandler} to be invoked on incoming messages, or null.
      */
     @UiThread
-    void setMessageHandler(String channel, BinaryMessageHandler handler);
+    void setMessageHandler(@NonNull String channel, @Nullable BinaryMessageHandler handler);
 
     /**
      * Handler for incoming binary messages from Flutter.
@@ -82,7 +84,7 @@ public interface BinaryMessenger {
          * @param reply A {@link BinaryReply} used for submitting a reply back to Flutter.
          */
         @UiThread
-        void onMessage(ByteBuffer message, BinaryReply reply);
+        void onMessage(@Nullable ByteBuffer message, @NonNull BinaryReply reply);
     }
 
     /**
@@ -99,6 +101,6 @@ public interface BinaryMessenger {
          * Reply receivers can read from the buffer directly.
          */
         @UiThread
-        void reply(ByteBuffer reply);
+        void reply(@Nullable ByteBuffer reply);
     }
 }

shell/platform/android/io/flutter/plugin/common/MessageCodec.java

@@ -4,6 +4,8 @@
 
 package io.flutter.plugin.common;
 
+import android.support.annotation.Nullable;
+
 import java.nio.ByteBuffer;
 
 /**
@@ -19,7 +21,8 @@ public interface MessageCodec<T> {
      * @return a ByteBuffer containing the encoding between position 0 and
      * the current position, or null, if message is null.
      */
-    ByteBuffer encodeMessage(T message);
+    @Nullable
+    ByteBuffer encodeMessage(@Nullable T message);
 
     /**
      * Decodes the specified message from binary.
@@ -28,5 +31,6 @@ public interface MessageCodec<T> {
      * @return a T value representation of the bytes between the given buffer's current
      * position and its limit, or null, if message is null.
      */
-    T decodeMessage(ByteBuffer message);
+    @Nullable
+    T decodeMessage(@Nullable ByteBuffer message);
 }

shell/platform/android/io/flutter/plugin/common/MethodChannel.java

@@ -142,7 +142,7 @@ public final class MethodChannel {
          * @param result A {@link Result} used for submitting the result of the call.
          */
         @UiThread
-        void onMethodCall(MethodCall call, Result result);
+        void onMethodCall(@NonNull MethodCall call, @NonNull Result result);
     }
 
     /**