[image_picker] Add desktop support - platform interface (#4161)

Platform interface portion of #3882

Adds CameraDelegatingImagePickerPlatform and ImagePickerCameraDelegate, and supportsImageSource

Part of flutter/flutter#102115
Part of flutter/flutter#102320
Part of flutter/flutter#85100

Author: stuartmorgan-g

packages/image_picker/image_picker_platform_interface/CHANGELOG.md

@@ -1,3 +1,11 @@
+## 2.7.0
+
+* Adds `CameraDelegatingImagePickerPlatform` as a base class for platform
+  implementations that don't support `ImageSource.camera`, but allow for an-
+  implementation to be provided at the application level via implementation
+  of `CameraDelegatingImagePickerPlatform`.
+* Adds `supportsImageSource` to check source support at runtime.
+
 ## 2.6.4
 
 * Adds compatibility with `http` 1.0.
@@ -32,7 +40,7 @@
     * Adds `requestFullMetadata` option that allows disabling extra permission requests
       on certain platforms.
     * Moves optional image picking parameters to `ImagePickerOptions` class.
-* Minor fixes for new analysis options. 
+* Minor fixes for new analysis options.
 
 ## 2.4.4
 

packages/image_picker/image_picker_platform_interface/lib/src/platform_interface/image_picker_platform.dart

@@ -32,8 +32,6 @@ abstract class ImagePickerPlatform extends PlatformInterface {
 
   /// Platform-specific plugins should set this with their own platform-specific
   /// class that extends [ImagePickerPlatform] when they register themselves.
-  // TODO(amirh): Extract common platform interface logic.
-  // https://github.com/flutter/flutter/issues/43368
   static set instance(ImagePickerPlatform instance) {
     PlatformInterface.verify(instance, _token);
     _instance = instance;
@@ -305,4 +303,75 @@ abstract class ImagePickerPlatform extends PlatformInterface {
     );
     return pickedImages ?? <XFile>[];
   }
+
+  /// Returns true if the implementation supports [source].
+  ///
+  /// Defaults to true for the original image sources, `gallery` and `camera`,
+  /// for backwards compatibility.
+  bool supportsImageSource(ImageSource source) {
+    return source == ImageSource.gallery || source == ImageSource.camera;
+  }
+}
+
+/// A base class for an [ImagePickerPlatform] implementation that does not
+/// directly support [ImageSource.camera], but supports delegating to a
+/// provided [ImagePickerCameraDelegate].
+abstract class CameraDelegatingImagePickerPlatform extends ImagePickerPlatform {
+  /// A delegate to respond to calls that use [ImageSource.camera].
+  ///
+  /// When it is null, attempting to use [ImageSource.camera] will throw a
+  /// [StateError].
+  ImagePickerCameraDelegate? cameraDelegate;
+
+  @override
+  bool supportsImageSource(ImageSource source) {
+    if (source == ImageSource.camera) {
+      return cameraDelegate != null;
+    }
+    return super.supportsImageSource(source);
+  }
+
+  @override
+  Future<XFile?> getImageFromSource({
+    required ImageSource source,
+    ImagePickerOptions options = const ImagePickerOptions(),
+  }) async {
+    if (source == ImageSource.camera) {
+      final ImagePickerCameraDelegate? delegate = cameraDelegate;
+      if (delegate == null) {
+        throw StateError(
+            'This implementation of ImagePickerPlatform requires a '
+            '"cameraDelegate" in order to use ImageSource.camera');
+      }
+      return delegate.takePhoto(
+          options: ImagePickerCameraDelegateOptions(
+        preferredCameraDevice: options.preferredCameraDevice,
+      ));
+    }
+    return super.getImageFromSource(source: source, options: options);
+  }
+
+  @override
+  Future<XFile?> getVideo({
+    required ImageSource source,
+    CameraDevice preferredCameraDevice = CameraDevice.rear,
+    Duration? maxDuration,
+  }) async {
+    if (source == ImageSource.camera) {
+      final ImagePickerCameraDelegate? delegate = cameraDelegate;
+      if (delegate == null) {
+        throw StateError(
+            'This implementation of ImagePickerPlatform requires a '
+            '"cameraDelegate" in order to use ImageSource.camera');
+      }
+      return delegate.takeVideo(
+          options: ImagePickerCameraDelegateOptions(
+              preferredCameraDevice: preferredCameraDevice,
+              maxVideoDuration: maxDuration));
+    }
+    return super.getVideo(
+        source: source,
+        preferredCameraDevice: preferredCameraDevice,
+        maxDuration: maxDuration);
+  }
 }

packages/image_picker/image_picker_platform_interface/lib/src/types/camera_delegate.dart

@@ -0,0 +1,53 @@
+// 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.
+
+import 'package:cross_file/cross_file.dart';
+import 'package:flutter/foundation.dart' show immutable;
+
+import 'camera_device.dart';
+
+/// Options for [ImagePickerCameraDelegate] methods.
+///
+/// New options may be added in the future.
+@immutable
+class ImagePickerCameraDelegateOptions {
+  /// Creates a new set of options for taking an image or video.
+  const ImagePickerCameraDelegateOptions({
+    this.preferredCameraDevice = CameraDevice.rear,
+    this.maxVideoDuration,
+  });
+
+  /// The camera device to default to, if available.
+  ///
+  /// Defaults to [CameraDevice.rear].
+  final CameraDevice preferredCameraDevice;
+
+  /// The maximum duration to allow when recording a video.
+  ///
+  /// Defaults to null, meaning no maximum duration.
+  final Duration? maxVideoDuration;
+}
+
+/// A delegate for `ImagePickerPlatform` implementations that do not provide
+/// a camera implementation, or that have a default but allow substituting an
+/// alternate implementation.
+abstract class ImagePickerCameraDelegate {
+  /// Takes a photo with the given [options] and returns an [XFile] to the
+  /// resulting image file.
+  ///
+  /// Returns null if the photo could not be taken, or the user cancelled.
+  Future<XFile?> takePhoto({
+    ImagePickerCameraDelegateOptions options =
+        const ImagePickerCameraDelegateOptions(),
+  });
+
+  /// Records a video with the given [options] and returns an [XFile] to the
+  /// resulting video file.
+  ///
+  /// Returns null if the video could not be recorded, or the user cancelled.
+  Future<XFile?> takeVideo({
+    ImagePickerCameraDelegateOptions options =
+        const ImagePickerCameraDelegateOptions(),
+  });
+}

packages/image_picker/image_picker_platform_interface/lib/src/types/types.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+export 'camera_delegate.dart';
 export 'camera_device.dart';
 export 'image_options.dart';
 export 'image_picker_options.dart';

packages/image_picker/image_picker_platform_interface/pubspec.yaml

@@ -4,7 +4,7 @@ repository: https://github.com/flutter/packages/tree/main/packages/image_picker/
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+image_picker%22
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 2.6.4
+version: 2.7.0
 
 environment:
   sdk: ">=2.18.0 <4.0.0"

packages/image_picker/image_picker_platform_interface/test/image_picker_platform_test.dart

@@ -0,0 +1,104 @@
+// 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.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:image_picker_platform_interface/image_picker_platform_interface.dart';
+
+void main() {
+  group('ImagePickerPlatform', () {
+    test('supportsImageSource defaults to true for original values', () async {
+      final ImagePickerPlatform implementation = FakeImagePickerPlatform();
+
+      expect(implementation.supportsImageSource(ImageSource.camera), true);
+      expect(implementation.supportsImageSource(ImageSource.gallery), true);
+    });
+  });
+
+  group('CameraDelegatingImagePickerPlatform', () {
+    test(
+        'supportsImageSource returns false for camera when there is no delegate',
+        () async {
+      final FakeCameraDelegatingImagePickerPlatform implementation =
+          FakeCameraDelegatingImagePickerPlatform();
+
+      expect(implementation.supportsImageSource(ImageSource.camera), false);
+    });
+
+    test('supportsImageSource returns true for camera when there is a delegate',
+        () async {
+      final FakeCameraDelegatingImagePickerPlatform implementation =
+          FakeCameraDelegatingImagePickerPlatform();
+      implementation.cameraDelegate = FakeCameraDelegate();
+
+      expect(implementation.supportsImageSource(ImageSource.camera), true);
+    });
+
+    test('getImageFromSource for camera throws if delegate is not set',
+        () async {
+      final FakeCameraDelegatingImagePickerPlatform implementation =
+          FakeCameraDelegatingImagePickerPlatform();
+
+      await expectLater(
+          implementation.getImageFromSource(source: ImageSource.camera),
+          throwsStateError);
+    });
+
+    test('getVideo for camera throws if delegate is not set', () async {
+      final FakeCameraDelegatingImagePickerPlatform implementation =
+          FakeCameraDelegatingImagePickerPlatform();
+
+      await expectLater(implementation.getVideo(source: ImageSource.camera),
+          throwsStateError);
+    });
+
+    test('getImageFromSource for camera calls delegate if set', () async {
+      const String fakePath = '/tmp/foo';
+      final FakeCameraDelegatingImagePickerPlatform implementation =
+          FakeCameraDelegatingImagePickerPlatform();
+      implementation.cameraDelegate =
+          FakeCameraDelegate(result: XFile(fakePath));
+
+      expect(
+          (await implementation.getImageFromSource(source: ImageSource.camera))!
+              .path,
+          fakePath);
+    });
+
+    test('getVideo for camera calls delegate if set', () async {
+      const String fakePath = '/tmp/foo';
+      final FakeCameraDelegatingImagePickerPlatform implementation =
+          FakeCameraDelegatingImagePickerPlatform();
+      implementation.cameraDelegate =
+          FakeCameraDelegate(result: XFile(fakePath));
+
+      expect((await implementation.getVideo(source: ImageSource.camera))!.path,
+          fakePath);
+    });
+  });
+}
+
+class FakeImagePickerPlatform extends ImagePickerPlatform {}
+
+class FakeCameraDelegatingImagePickerPlatform
+    extends CameraDelegatingImagePickerPlatform {}
+
+class FakeCameraDelegate extends ImagePickerCameraDelegate {
+  FakeCameraDelegate({this.result});
+
+  XFile? result;
+
+  @override
+  Future<XFile?> takePhoto(
+      {ImagePickerCameraDelegateOptions options =
+          const ImagePickerCameraDelegateOptions()}) async {
+    return result;
+  }
+
+  @override
+  Future<XFile?> takeVideo(
+      {ImagePickerCameraDelegateOptions options =
+          const ImagePickerCameraDelegateOptions()}) async {
+    return result;
+  }
+}