[camerax] Implement onCameraClosing (#3878)

### Overview

Continuation of #3419.

Implements onCameraClosing that will send an event anytime the camera closes, as detected by observing the LiveData of the CameraState of the current camera being used in the plugin.

Fixes flutter/flutter#121162.

### Highlights of what has changed since the latest reviews of the [last PR](#3419):

- Wrapped `LiveData#getValue` ([docs](https://developer.android.com/reference/androidx/lifecycle/LiveData#getValue())) for the purposes of retrieving current value `LiveData<ZoomState>` to properly implement retrieving zoom information
- Modified Dart Host API and FlutterAPI implementations' documentation on their `binaryMessenger` and `instanceManager` documentation to be clearer as per suggestion from comments on the original PR
- Changed `binaryMessenger` and `instanceManager` fields to be private in Flutter API implementations
- Removed `cast` method and added enum `LiveDataSupportedType` to pigeon file to use for safely casting the `LiveData` generic when received on the Dart or native side.
- Moved `CameraStateError` code decoding to Dart side as this was written by me and not directly provided by CameraX.
- Added tests for the conversion of objects.
- The following issues were filed to capture feedback given but not addressed in this PR: flutter/flutter#125926, flutter/flutter#125928.

Author: camsim99

packages/camera/camera_android_camerax/CHANGELOG.md

@@ -23,3 +23,5 @@
 * Implements retrieval of camera information.
 * Updates README.md with plugin overview and adds contribution guide to CONTRIBUTING.md.
 * Implements video capture.
+* Implements onCameraClosing callback method for indicating the camera is closing and bumps CameraX version to 1.3.0-alpha05.
+

packages/camera/camera_android_camerax/android/build.gradle

@@ -62,7 +62,7 @@ android {
 
 dependencies {
     // CameraX core library using the camera2 implementation must use same version number.
-    def camerax_version = "1.3.0-alpha04"
+    def camerax_version = "1.3.0-alpha05"
     implementation "androidx.camera:camera-core:${camerax_version}"
     implementation "androidx.camera:camera-camera2:${camerax_version}"
     implementation "androidx.camera:camera-lifecycle:${camerax_version}"

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

@@ -26,7 +26,10 @@ public final class CameraAndroidCameraxPlugin implements FlutterPlugin, Activity
   private ImageCaptureHostApiImpl imageCaptureHostApiImpl;
   public SystemServicesHostApiImpl systemServicesHostApiImpl;
 
-  @VisibleForTesting ProcessCameraProviderHostApiImpl processCameraProviderHostApiImpl;
+  @VisibleForTesting @NonNull
+  public ProcessCameraProviderHostApiImpl processCameraProviderHostApiImpl;
+
+  @VisibleForTesting @NonNull public LiveDataHostApiImpl liveDataHostApiImpl;
 
   /**
    * Initialize this within the {@code #configureFlutterEngine} of a Flutter activity or fragment.
@@ -71,6 +74,12 @@ public void setUp(
     imageCaptureHostApiImpl =
         new ImageCaptureHostApiImpl(binaryMessenger, instanceManager, context);
     GeneratedCameraXLibrary.ImageCaptureHostApi.setup(binaryMessenger, imageCaptureHostApiImpl);
+    GeneratedCameraXLibrary.CameraHostApi.setup(
+        binaryMessenger, new CameraHostApiImpl(binaryMessenger, instanceManager));
+    liveDataHostApiImpl = new LiveDataHostApiImpl(binaryMessenger, instanceManager);
+    GeneratedCameraXLibrary.LiveDataHostApi.setup(binaryMessenger, liveDataHostApiImpl);
+    GeneratedCameraXLibrary.ObserverHostApi.setup(
+        binaryMessenger, new ObserverHostApiImpl(binaryMessenger, instanceManager));
     imageAnalysisHostApiImpl = new ImageAnalysisHostApiImpl(binaryMessenger, instanceManager);
     GeneratedCameraXLibrary.ImageAnalysisHostApi.setup(binaryMessenger, imageAnalysisHostApiImpl);
     GeneratedCameraXLibrary.AnalyzerHostApi.setup(
@@ -105,19 +114,18 @@ public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
 
   @Override
   public void onAttachedToActivity(@NonNull ActivityPluginBinding activityPluginBinding) {
-    setUp(
-        pluginBinding.getBinaryMessenger(),
-        pluginBinding.getApplicationContext(),
-        pluginBinding.getTextureRegistry());
-    updateContext(pluginBinding.getApplicationContext());
-
     Activity activity = activityPluginBinding.getActivity();
 
+    setUp(pluginBinding.getBinaryMessenger(), activity, pluginBinding.getTextureRegistry());
+    updateContext(activity);
+
     if (activity instanceof LifecycleOwner) {
       processCameraProviderHostApiImpl.setLifecycleOwner((LifecycleOwner) activity);
+      liveDataHostApiImpl.setLifecycleOwner((LifecycleOwner) activity);
     } else {
       ProxyLifecycleProvider proxyLifecycleProvider = new ProxyLifecycleProvider(activity);
       processCameraProviderHostApiImpl.setLifecycleOwner(proxyLifecycleProvider);
+      liveDataHostApiImpl.setLifecycleOwner(proxyLifecycleProvider);
     }
 
     systemServicesHostApiImpl.setActivity(activity);

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

@@ -31,10 +31,11 @@ public Long getCameraInfo(@NonNull Long identifier) {
     Camera camera = (Camera) Objects.requireNonNull(instanceManager.getInstance(identifier));
     CameraInfo cameraInfo = camera.getCameraInfo();
 
-    CameraInfoFlutterApiImpl cameraInfoFlutterApiImpl =
-        new CameraInfoFlutterApiImpl(binaryMessenger, instanceManager);
-    cameraInfoFlutterApiImpl.create(cameraInfo, reply -> {});
-
+    if (!instanceManager.containsInstance(cameraInfo)) {
+      CameraInfoFlutterApiImpl cameraInfoFlutterApiImpl =
+          new CameraInfoFlutterApiImpl(binaryMessenger, instanceManager);
+      cameraInfoFlutterApiImpl.create(cameraInfo, reply -> {});
+    }
     return instanceManager.getIdentifierForStrongReference(cameraInfo);
   }
 }

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

@@ -17,6 +17,9 @@ public CameraInfoFlutterApiImpl(
     this.instanceManager = instanceManager;
   }
 
+  /**
+   * Creates a {@link CameraInfo} instance in Dart. {@code reply} is not used so it can be empty.
+   */
   void create(CameraInfo cameraInfo, Reply<Void> reply) {
     if (!instanceManager.containsInstance(cameraInfo)) {
       create(instanceManager.addHostCreatedInstance(cameraInfo), reply);

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

@@ -5,24 +5,35 @@
 package io.flutter.plugins.camerax;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
 import androidx.camera.core.CameraInfo;
+import androidx.camera.core.CameraState;
 import androidx.camera.core.ExposureState;
 import androidx.camera.core.ZoomState;
+import androidx.lifecycle.LiveData;
 import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugins.camerax.GeneratedCameraXLibrary.CameraInfoHostApi;
+import io.flutter.plugins.camerax.GeneratedCameraXLibrary.LiveDataSupportedType;
 import java.util.Objects;
 
 public class CameraInfoHostApiImpl implements CameraInfoHostApi {
   private final BinaryMessenger binaryMessenger;
   private final InstanceManager instanceManager;
 
+  @VisibleForTesting public LiveDataFlutterApiWrapper liveDataFlutterApiWrapper;
+
   public CameraInfoHostApiImpl(
       @NonNull BinaryMessenger binaryMessenger, @NonNull InstanceManager instanceManager) {
     this.binaryMessenger = binaryMessenger;
     this.instanceManager = instanceManager;
+    this.liveDataFlutterApiWrapper =
+        new LiveDataFlutterApiWrapper(binaryMessenger, instanceManager);
   }
 
-  /** Retrieves the sensor rotation in degrees, relative to the device's default orientation. */
+  /**
+   * Retrieves the sensor rotation degrees of the {@link androidx.camera.core.Camera} that is
+   * represented by the {@link CameraInfo} with the specified identifier.
+   */
   @Override
   @NonNull
   public Long getSensorRotationDegrees(@NonNull Long identifier) {
@@ -31,6 +42,22 @@ public Long getSensorRotationDegrees(@NonNull Long identifier) {
     return Long.valueOf(cameraInfo.getSensorRotationDegrees());
   }
 
+  /**
+   * Retrieves the {@link LiveData} of the {@link CameraState} that is tied to the {@link
+   * androidx.camera.core.Camera} that is represented by the {@link CameraInfo} with the specified
+   * identifier.
+   */
+  @Override
+  @NonNull
+  public Long getCameraState(@NonNull Long identifier) {
+    CameraInfo cameraInfo =
+        (CameraInfo) Objects.requireNonNull(instanceManager.getInstance(identifier));
+    LiveData<CameraState> liveCameraState = cameraInfo.getCameraState();
+    liveDataFlutterApiWrapper.create(
+        liveCameraState, LiveDataSupportedType.CAMERA_STATE, reply -> {});
+    return instanceManager.getIdentifierForStrongReference(liveCameraState);
+  }
+
   /**
    * Retrieves the {@link ExposureState} of the {@link CameraInfo} with the specified identifier.
    */
@@ -49,20 +76,19 @@ public Long getExposureState(@NonNull Long identifier) {
   }
 
   /**
-   * Retrieves the current {@link ZoomState} value of the {@link CameraInfo} with the specified
-   * identifier.
+   * Retrieves the {@link LiveData} of the {@link ZoomState} of the {@link CameraInfo} with the
+   * specified identifier.
    */
   @NonNull
   @Override
   public Long getZoomState(@NonNull Long identifier) {
     CameraInfo cameraInfo =
         (CameraInfo) Objects.requireNonNull(instanceManager.getInstance(identifier));
-    // TODO(camsim99): Create/return LiveData<ZoomState> once https://github.com/flutter/packages/pull/3419 lands.
-    ZoomState zoomState = cameraInfo.getZoomState().getValue();
+    LiveData<ZoomState> zoomState = cameraInfo.getZoomState();
 
-    ZoomStateFlutterApiImpl zoomStateFlutterApiImpl =
-        new ZoomStateFlutterApiImpl(binaryMessenger, instanceManager);
-    zoomStateFlutterApiImpl.create(zoomState, result -> {});
+    LiveDataFlutterApiWrapper liveDataFlutterApiWrapper =
+        new LiveDataFlutterApiWrapper(binaryMessenger, instanceManager);
+    liveDataFlutterApiWrapper.create(zoomState, LiveDataSupportedType.ZOOM_STATE, reply -> {});
 
     return instanceManager.getIdentifierForStrongReference(zoomState);
   }

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

@@ -0,0 +1,57 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugins.camerax;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+import androidx.camera.core.CameraState;
+import io.flutter.plugin.common.BinaryMessenger;
+import io.flutter.plugins.camerax.GeneratedCameraXLibrary.CameraStateErrorFlutterApi;
+
+/**
+ * Flutter API implementation for {@link CameraStateError}.
+ *
+ * <p>This class may handle adding native instances that are attached to a Dart instance or passing
+ * arguments of callbacks methods to a Dart instance.
+ */
+public class CameraStateErrorFlutterApiWrapper {
+  private final BinaryMessenger binaryMessenger;
+  private final InstanceManager instanceManager;
+  private CameraStateErrorFlutterApi cameraStateErrorFlutterApi;
+
+  /**
+   * Constructs a {@link CameraStateErrorFlutterApiWrapper}.
+   *
+   * @param binaryMessenger used to communicate with Dart over asynchronous messages
+   * @param instanceManager maintains instances stored to communicate with attached Dart objects
+   */
+  public CameraStateErrorFlutterApiWrapper(
+      @NonNull BinaryMessenger binaryMessenger, @NonNull InstanceManager instanceManager) {
+    this.binaryMessenger = binaryMessenger;
+    this.instanceManager = instanceManager;
+    cameraStateErrorFlutterApi = new CameraStateErrorFlutterApi(binaryMessenger);
+  }
+
+  /**
+   * Stores the {@link CameraStateError} instance and notifies Dart to create and store a new {@link
+   * CameraStateError} instance that is attached to this one. If {@code instance} has already been
+   * added, this method does nothing.
+   */
+  public void create(
+      @NonNull CameraState.StateError instance,
+      @NonNull Long code,
+      @NonNull CameraStateErrorFlutterApi.Reply<Void> callback) {
+    if (!instanceManager.containsInstance(instance)) {
+      cameraStateErrorFlutterApi.create(
+          instanceManager.addHostCreatedInstance(instance), code, callback);
+    }
+  }
+
+  /** Sets the Flutter API used to send messages to Dart. */
+  @VisibleForTesting
+  void setApi(@NonNull CameraStateErrorFlutterApi api) {
+    this.cameraStateErrorFlutterApi = api;
+  }
+}

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

@@ -0,0 +1,102 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugins.camerax;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
+import androidx.camera.core.CameraState;
+import io.flutter.plugin.common.BinaryMessenger;
+import io.flutter.plugins.camerax.GeneratedCameraXLibrary.CameraStateFlutterApi;
+import io.flutter.plugins.camerax.GeneratedCameraXLibrary.CameraStateType;
+import io.flutter.plugins.camerax.GeneratedCameraXLibrary.CameraStateTypeData;
+
+/**
+ * Flutter API implementation for {@link CameraState}.
+ *
+ * <p>This class may handle adding native instances that are attached to a Dart instance or passing
+ * arguments of callbacks methods to a Dart instance.
+ */
+public class CameraStateFlutterApiWrapper {
+  private final BinaryMessenger binaryMessenger;
+  private final InstanceManager instanceManager;
+  private CameraStateFlutterApi cameraStateFlutterApi;
+
+  /**
+   * Constructs a {@link CameraStateFlutterApiWrapper}.
+   *
+   * @param binaryMessenger used to communicate with Dart over asynchronous messages
+   * @param instanceManager maintains instances stored to communicate with attached Dart objects
+   */
+  public CameraStateFlutterApiWrapper(
+      @NonNull BinaryMessenger binaryMessenger, @NonNull InstanceManager instanceManager) {
+    this.binaryMessenger = binaryMessenger;
+    this.instanceManager = instanceManager;
+    cameraStateFlutterApi = new CameraStateFlutterApi(binaryMessenger);
+  }
+
+  /**
+   * Stores the {@link CameraState} instance and notifies Dart to create and store a new {@link
+   * CameraState} instance that is attached to this one. If {@code instance} has already been added,
+   * this method does nothing.
+   */
+  public void create(
+      @NonNull CameraState instance,
+      @NonNull CameraStateType type,
+      @Nullable CameraState.StateError error,
+      @NonNull CameraStateFlutterApi.Reply<Void> callback) {
+    if (instanceManager.containsInstance(instance)) {
+      return;
+    }
+
+    if (error != null) {
+      // if there is a problem with the current camera state, we need to create a CameraStateError
+      // to send to the Dart side.
+      new CameraStateErrorFlutterApiWrapper(binaryMessenger, instanceManager)
+          .create(error, Long.valueOf(error.getCode()), reply -> {});
+    }
+
+    cameraStateFlutterApi.create(
+        instanceManager.addHostCreatedInstance(instance),
+        new CameraStateTypeData.Builder().setValue(type).build(),
+        instanceManager.getIdentifierForStrongReference(error),
+        callback);
+  }
+
+  /** Converts CameraX CameraState.Type to CameraStateType that the Dart side understands. */
+  @NonNull
+  public static CameraStateType getCameraStateType(@NonNull CameraState.Type type) {
+    CameraStateType cameraStateType = null;
+    switch (type) {
+      case CLOSED:
+        cameraStateType = CameraStateType.CLOSED;
+        break;
+      case CLOSING:
+        cameraStateType = CameraStateType.CLOSING;
+        break;
+      case OPEN:
+        cameraStateType = CameraStateType.OPEN;
+        break;
+      case OPENING:
+        cameraStateType = CameraStateType.OPENING;
+        break;
+      case PENDING_OPEN:
+        cameraStateType = CameraStateType.PENDING_OPEN;
+        break;
+    }
+
+    if (cameraStateType == null) {
+      throw new IllegalArgumentException(
+          "The CameraState.Type passed to this method was not recognized.");
+    }
+    return cameraStateType;
+  }
+
+  /** Sets the Flutter API used to send messages to Dart. */
+  @VisibleForTesting
+  void setApi(@NonNull CameraStateFlutterApi api) {
+    this.cameraStateFlutterApi = api;
+  }
+}

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

@@ -32,10 +32,12 @@ public CameraSelector.Builder createCameraSelectorBuilder() {
     return new CameraSelector.Builder();
   }
 
+  /** Creates an instance of {@link CameraPermissionsManager}. */
   public CameraPermissionsManager createCameraPermissionsManager() {
     return new CameraPermissionsManager();
   }
 
+  /** Creates an instance of the {@link DeviceOrientationManager}. */
   public DeviceOrientationManager createDeviceOrientationManager(
       @NonNull Activity activity,
       @NonNull Boolean isFrontFacing,
@@ -44,16 +46,18 @@ public DeviceOrientationManager createDeviceOrientationManager(
     return new DeviceOrientationManager(activity, isFrontFacing, sensorOrientation, callback);
   }
 
+  /** Creates a builder for an instance of the {@link Preview} use case. */
   public Preview.Builder createPreviewBuilder() {
     return new Preview.Builder();
   }
 
+  /** Creates a {@link Surface} instance from the specified {@link SurfaceTexture}. */
   public Surface createSurface(@NonNull SurfaceTexture surfaceTexture) {
     return new Surface(surfaceTexture);
   }
 
   /**
-   * Creates an instance of the {@code SystemServicesFlutterApiImpl}.
+   * Creates an instance of the {@link SystemServicesFlutterApiImpl}.
    *
    * <p>Included in this class to utilize the callback methods it provides, e.g. {@code
    * onCameraError(String)}.
@@ -69,6 +73,7 @@ public Recorder.Builder createRecorderBuilder() {
     return new Recorder.Builder();
   }
 
+  /** Creates a builder for an instance of the {@link ImageCapture} use case. */
   @NonNull
   public ImageCapture.Builder createImageCaptureBuilder() {
     return new ImageCapture.Builder();