Address rest of review

packages/camera/camera_android_camerax/android/src/main/java/io/flutter/plugins/camerax/LiveDataHostApiImpl.java

@@ -74,25 +74,32 @@ public Long getValue(@NonNull Long identifier, @NonNull LiveDataSupportedTypeDat
     LiveDataSupportedType valueType = type.getValue();
     switch (valueType) {
       case CAMERA_STATE:
-        CameraState cameraState = (CameraState) value;
-        new CameraStateFlutterApiWrapper(binaryMessenger, instanceManager)
-            .create(
-                cameraState,
-                CameraStateFlutterApiWrapper.getCameraStateType(cameraState.getType()),
-                cameraState.getError(),
-                reply -> {});
-        return instanceManager.getIdentifierForStrongReference(cameraState);
+        return createCameraState((CameraState) value);
       case ZOOM_STATE:
-        ZoomState zoomState = (ZoomState) value;
-        new ZoomStateFlutterApiImpl(binaryMessenger, instanceManager)
-            .create(zoomState, reply -> {});
-        return instanceManager.getIdentifierForStrongReference(zoomState);
+        return createZoomState((ZoomState) value);
       default:
         throw new IllegalArgumentException(
             "The type of LiveData whose value was requested is not supported.");
     }
   }
 
+  /** Creates a {@link CameraState} on the Dart side and returns its identifier. */
+  private Long createCameraState(CameraState cameraState) {
+    new CameraStateFlutterApiWrapper(binaryMessenger, instanceManager)
+        .create(
+            cameraState,
+            CameraStateFlutterApiWrapper.getCameraStateType(cameraState.getType()),
+            cameraState.getError(),
+            reply -> {});
+    return instanceManager.getIdentifierForStrongReference(cameraState);
+  }
+
+  /** Creates a {@link ZoomState} on the Dart side and returns its identifiers. */
+  private Long createZoomState(ZoomState zoomState) {
+    new ZoomStateFlutterApiImpl(binaryMessenger, instanceManager).create(zoomState, reply -> {});
+    return instanceManager.getIdentifierForStrongReference(zoomState);
+  }
+
   /** Retrieves the {@link LiveData} instance that has the specified identifier. */
   private LiveData<?> getLiveDataInstance(@NonNull Long identifier) {
     return Objects.requireNonNull(instanceManager.getInstance(identifier));

packages/camera/camera_android_camerax/android/src/main/java/io/flutter/plugins/camerax/ObserverFlutterApiWrapper.java

@@ -49,31 +49,21 @@ public ObserverFlutterApiWrapper(
    * Sends a message to Dart to call {@link Observer.onChanged} on the Dart object representing
    * {@code instance}.
    */
-  public void onChanged(
-      @NonNull Observer<?> instance,
-      @NonNull Object value,
+  public <T> void onChanged(
+      @NonNull Observer<T> instance,
+      @NonNull T value,
       @NonNull ObserverFlutterApi.Reply<Void> callback) {
 
-    // Cast value to type of data that is being observed if supported by this plugin.
+    // Cast value to type of data that is being observed and create it on the Dart side
+    // if supported by this plugin.
+    //
+    // The supported types can be found in GeneratedCameraXLibrary.java as the
+    // LiveDataSupportedType enum. To add a new type, please follow the instructions
+    // found in pigeons/camerax_library.dart in the documentation for LiveDataSupportedType.
     if (value instanceof CameraState) {
-      CameraState state = (CameraState) value;
-
-      if (cameraStateFlutterApiWrapper == null) {
-        cameraStateFlutterApiWrapper =
-            new CameraStateFlutterApiWrapper(binaryMessenger, instanceManager);
-      }
-      cameraStateFlutterApiWrapper.create(
-          state,
-          CameraStateFlutterApiWrapper.getCameraStateType(state.getType()),
-          state.getError(),
-          reply -> {});
+      createCameraState((CameraState) value);
     } else if (value instanceof ZoomState) {
-      ZoomState state = (ZoomState) value;
-
-      if (zoomStateFlutterApiImpl == null) {
-        zoomStateFlutterApiImpl = new ZoomStateFlutterApiImpl(binaryMessenger, instanceManager);
-      }
-      zoomStateFlutterApiImpl.create(state, reply -> {});
+      createZoomState((ZoomState) value);
     } else {
       throw new UnsupportedOperationException(
           "The type of value that was observed is not handled by this plugin.");
@@ -93,6 +83,27 @@ public void onChanged(
         callback);
   }
 
+  /** Creates a {@link CameraState} on the Dart side. */
+  private void createCameraState(CameraState cameraState) {
+    if (cameraStateFlutterApiWrapper == null) {
+      cameraStateFlutterApiWrapper =
+          new CameraStateFlutterApiWrapper(binaryMessenger, instanceManager);
+    }
+    cameraStateFlutterApiWrapper.create(
+        cameraState,
+        CameraStateFlutterApiWrapper.getCameraStateType(cameraState.getType()),
+        cameraState.getError(),
+        reply -> {});
+  }
+
+  /** Creates a {@link ZoomState} on the Dart side. */
+  private void createZoomState(ZoomState zoomState) {
+    if (zoomStateFlutterApiImpl == null) {
+      zoomStateFlutterApiImpl = new ZoomStateFlutterApiImpl(binaryMessenger, instanceManager);
+    }
+    zoomStateFlutterApiImpl.create(zoomState, reply -> {});
+  }
+
   /** Sets the Flutter API used to send messages to Dart. */
   @VisibleForTesting
   void setApi(@NonNull ObserverFlutterApi api) {

packages/camera/camera_android_camerax/android/src/test/java/io/flutter/plugins/camerax/LiveDataTest.java

@@ -124,8 +124,10 @@ public void getValue_returnsExpectedValue() {
               hostApi.getValue(mockLiveZoomStateIdentifier, typeData), mockZoomStateIdentifier);
           break;
         default:
-          // There is a LiveDataSupportedType untested by this method.
-          fail();
+          fail(
+              "The LiveDataSupportedType "
+                  + supportedType.toString()
+                  + "is unhandled by this test.");
       }
     }
   }