[camerax] Change buildPreview to return Texture versus `FutureBui…

…lder` (#6021)

Changes the `buildPreview` implementation to return a `Texture` versus a `FutureBuilder` that would ultimately return that same `Texture`.

The `FutureBuilder` depended on checking a condition that should be true by default assuming `createCamera` was called prior. This seems to be an assumption made consistently across other platform implementations (including `camera_android`-- see [source](https://github.com/flutter/packages/blob/7b1ae1f4cceea02f330716e701c6dcd9f0ca3f7e/packages/camera/camera_android/lib/src/android_camera.dart#L520)), so this PR is achieving consistency with them.

Fixes flutter/flutter#140567. Thanks to @davidmartos96 for the push to investigate deeper on that issue!

packages/camera/camera_android_camerax/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 0.5.0+29
+
+* Modifies `buildPreview` to return `Texture` that maps to camera preview, building in the assumption
+  that `createCamera` should have been called before building the preview. Fixes
+  https://github.com/flutter/flutter/issues/140567.
+
 ## 0.5.0+28
 
 * Wraps CameraX classes needed to implement setting focus and exposure points and exposure offset.

packages/camera/camera_android_camerax/lib/src/android_camera_camerax.dart

@@ -98,6 +98,11 @@ class AndroidCameraCameraX extends CameraPlatform {
   @visibleForTesting
   String? videoOutputPath;
 
+  /// Whether or not [preview] has been bound to the lifecycle of the camera by
+  /// [createCamera].
+  @visibleForTesting
+  bool previewInitiallyBound = false;
+
   bool _previewIsPaused = false;
 
   /// The prefix used to create the filename for video recording files.
@@ -284,6 +289,7 @@ class AndroidCameraCameraX extends CameraPlatform {
     camera = await processCameraProvider!.bindToLifecycle(
         cameraSelector!, <UseCase>[preview!, imageCapture!, imageAnalysis!]);
     await _updateCameraInfoAndLiveCameraState(flutterSurfaceTextureId);
+    previewInitiallyBound = true;
     _previewIsPaused = false;
 
     return flutterSurfaceTextureId;
@@ -520,21 +526,20 @@ class AndroidCameraCameraX extends CameraPlatform {
   }
 
   /// Returns a widget showing a live camera preview.
+  ///
+  /// [createCamera] must be called before attempting to build this preview.
   @override
   Widget buildPreview(int cameraId) {
-    return FutureBuilder<void>(
-        future: _bindPreviewToLifecycle(cameraId),
-        builder: (BuildContext context, AsyncSnapshot<void> snapshot) {
-          switch (snapshot.connectionState) {
-            case ConnectionState.none:
-            case ConnectionState.waiting:
-            case ConnectionState.active:
-              // Do nothing while waiting for preview to be bound to lifecyle.
-              return const SizedBox.shrink();
-            case ConnectionState.done:
-              return Texture(textureId: cameraId);
-          }
-        });
+    if (!previewInitiallyBound) {
+      // No camera has been created, and thus, the preview UseCase has not been
+      // bound to the camera lifecycle, restricting this preview from being
+      // built.
+      throw CameraException(
+        'cameraNotFound',
+        "Camera not found. Please call the 'create' method before calling 'buildPreview'",
+      );
+    }
+    return Texture(textureId: cameraId);
   }
 
   /// Captures an image and returns the file where it was saved.

packages/camera/camera_android_camerax/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera_android_camerax
 description: Android implementation of the camera plugin using the CameraX library.
 repository: https://github.com/flutter/packages/tree/main/packages/camera/camera_android_camerax
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.5.0+28
+version: 0.5.0+29
 
 environment:
   sdk: ">=3.0.0 <4.0.0"

packages/camera/camera_android_camerax/test/android_camera_camerax_test.dart

@@ -388,6 +388,10 @@ void main() {
 
     // Verify the camera's CameraInfo instance got updated.
     expect(camera.cameraInfo, equals(mockCameraInfo));
+
+    // Verify preview has been marked as bound to the camera lifecycle by
+    // createCamera.
+    expect(camera.previewInitiallyBound, isTrue);
   });
 
   test(
@@ -971,83 +975,33 @@ void main() {
   });
 
   test(
-      'buildPreview returns a FutureBuilder that does not return a Texture until the preview is bound to the lifecycle',
+      'buildPreview throws an exception if the preview is not bound to the lifecycle',
       () async {
     final AndroidCameraCameraX camera = AndroidCameraCameraX();
-    final MockProcessCameraProvider mockProcessCameraProvider =
-        MockProcessCameraProvider();
-    final MockCamera mockCamera = MockCamera();
-    final MockCameraInfo mockCameraInfo = MockCameraInfo();
-    const int textureId = 75;
-
-    // Set directly for test versus calling createCamera.
-    camera.processCameraProvider = mockProcessCameraProvider;
-    camera.cameraSelector = MockCameraSelector();
-    camera.preview = MockPreview();
-
-    // Tell plugin to create a mock Observer<CameraState>, that is created to
-    // track camera state once preview is bound to the lifecycle.
-    camera.proxy =
-        CameraXProxy(createCameraStateObserver: (_) => MockObserver());
-
-    when(mockProcessCameraProvider
-            .bindToLifecycle(camera.cameraSelector, <UseCase>[camera.preview!]))
-        .thenAnswer((_) async => mockCamera);
-    when(mockCamera.getCameraInfo()).thenAnswer((_) async => mockCameraInfo);
-    when(mockCameraInfo.getCameraState())
-        .thenAnswer((_) async => MockLiveCameraState());
+    const int cameraId = 73;
 
-    final FutureBuilder<void> previewWidget =
-        camera.buildPreview(textureId) as FutureBuilder<void>;
+    // Tell camera that createCamera has not been called and thus, preview has
+    // not been bound to the lifecycle of the camera.
+    camera.previewInitiallyBound = false;
 
     expect(
-        previewWidget.builder(
-            MockBuildContext(), const AsyncSnapshot<void>.nothing()),
-        isA<SizedBox>());
-    expect(
-        previewWidget.builder(
-            MockBuildContext(), const AsyncSnapshot<void>.waiting()),
-        isA<SizedBox>());
-    expect(
-        previewWidget.builder(MockBuildContext(),
-            const AsyncSnapshot<void>.withData(ConnectionState.active, null)),
-        isA<SizedBox>());
+        () => camera.buildPreview(cameraId), throwsA(isA<CameraException>()));
   });
 
   test(
-      'buildPreview returns a FutureBuilder that returns a Texture once the preview is bound to the lifecycle',
+      'buildPreview returns a Texture once the preview is bound to the lifecycle',
       () async {
     final AndroidCameraCameraX camera = AndroidCameraCameraX();
-    final MockProcessCameraProvider mockProcessCameraProvider =
-        MockProcessCameraProvider();
-    final MockCamera mockCamera = MockCamera();
-    final MockCameraInfo mockCameraInfo = MockCameraInfo();
-    const int textureId = 75;
-
-    // Set directly for test versus calling createCamera.
-    camera.processCameraProvider = mockProcessCameraProvider;
-    camera.cameraSelector = MockCameraSelector();
-    camera.preview = MockPreview();
-
-    // Tell plugin to create a mock Observer<CameraState>, that is created to
-    // track camera state once preview is bound to the lifecycle.
-    camera.proxy =
-        CameraXProxy(createCameraStateObserver: (_) => MockObserver());
+    const int cameraId = 37;
 
-    when(mockProcessCameraProvider
-            .bindToLifecycle(camera.cameraSelector, <UseCase>[camera.preview!]))
-        .thenAnswer((_) async => mockCamera);
-    when(mockCamera.getCameraInfo()).thenAnswer((_) async => mockCameraInfo);
-    when(mockCameraInfo.getCameraState())
-        .thenAnswer((_) async => MockLiveCameraState());
+    // Tell camera that createCamera has been called and thus, preview has been
+    // bound to the lifecycle of the camera.
+    camera.previewInitiallyBound = true;
 
-    final FutureBuilder<void> previewWidget =
-        camera.buildPreview(textureId) as FutureBuilder<void>;
+    final Widget widget = camera.buildPreview(cameraId);
 
-    final Texture previewTexture = previewWidget.builder(MockBuildContext(),
-            const AsyncSnapshot<void>.withData(ConnectionState.done, null))
-        as Texture;
-    expect(previewTexture.textureId, equals(textureId));
+    expect(widget is Texture, isTrue);
+    expect((widget as Texture).textureId, cameraId);
   });
 
   group('video recording', () {