add feature to enable streaming image with torch on

packages/camera/android/src/main/java/io/flutter/plugins/camera/Camera.java

@@ -60,6 +60,7 @@ public class Camera {
   private boolean recordingVideo;
   private CamcorderProfile recordingProfile;
   private int currentOrientation = ORIENTATION_UNKNOWN;
+  private boolean isTorchOn = false;
 
   // Mirrors camera.dart
   public enum ResolutionPreset {
@@ -278,8 +279,7 @@ public void onCaptureFailed(
     }
   }
 
-  private void createCaptureSession(int templateType, Surface... surfaces)
-      throws CameraAccessException {
+  private void createCaptureSession(int templateType, Surface... surfaces) throws CameraAccessException {
     createCaptureSession(templateType, null, surfaces);
   }
 
@@ -318,8 +318,10 @@ public void onConfigured(@NonNull CameraCaptureSession session) {
                 return;
               }
               cameraCaptureSession = session;
-              captureRequestBuilder.set(
-                  CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
+              captureRequestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
+              if(isTorchOn){
+                captureRequestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_TORCH);
+              }
               cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
               if (onSuccessCallback != null) {
                 onSuccessCallback.run();
@@ -421,11 +423,13 @@ public void resumeVideoRecording(@NonNull final Result result) {
   }
 
   public void startPreview() throws CameraAccessException {
+    isTorchOn = false;
     createCaptureSession(CameraDevice.TEMPLATE_PREVIEW, pictureImageReader.getSurface());
   }
 
-  public void startPreviewWithImageStream(EventChannel imageStreamChannel)
+  public void startPreviewWithImageStream(EventChannel imageStreamChannel, boolean useTorch)
       throws CameraAccessException {
+    isTorchOn = useTorch;
     createCaptureSession(CameraDevice.TEMPLATE_RECORD, imageStreamReader.getSurface());
 
     imageStreamChannel.setStreamHandler(

packages/camera/android/src/main/java/io/flutter/plugins/camera/MethodCallHandlerImpl.java

@@ -106,7 +106,17 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull final Result result)
       case "startImageStream":
         {
           try {
-            camera.startPreviewWithImageStream(imageStreamChannel);
+            camera.startPreviewWithImageStream(imageStreamChannel, false);
+            result.success(null);
+          } catch (Exception e) {
+            handleException(e, result);
+          }
+          break;
+        }
+      case "startImageStreamWithTorch":
+        {
+          try {
+            camera.startPreviewWithImageStream(imageStreamChannel, true);
             result.success(null);
           } catch (Exception e) {
             handleException(e, result);

packages/camera/example/lib/main.dart

@@ -110,6 +110,10 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
               children: <Widget>[
                 _cameraTogglesRowWidget(),
                 _thumbnailWidget(),
+                FlatButton(
+                  onPressed: () => controller.startImageStreamWithTorch((image) => print(imagePath)),
+                  child: Text('Stream with Torch'),
+                )
               ],
             ),
           ),

packages/camera/lib/camera.dart

@@ -414,6 +414,55 @@ class CameraController extends ValueNotifier<CameraValue> {
     );
   }
 
+  /// Start streaming images from platform camera with torch on.
+  ///
+  /// Settings for capturing images on iOS and Android is set to always use the
+  /// latest image available from the camera and will drop all other images.
+  ///
+  /// When running continuously with [CameraPreview] widget, this function runs
+  /// best with [ResolutionPreset.low]. Running on [ResolutionPreset.high] can
+  /// have significant frame rate drops for [CameraPreview] on lower end
+  /// devices.
+  ///
+  /// Throws a [CameraException] if image streaming or video recording has
+  /// already started.
+  // TODO(bmparr): Add settings for resolution and fps.
+  Future<void> startImageStreamWithTorch(onLatestImageAvailable onAvailable) async {
+    if (!value.isInitialized || _isDisposed) {
+      throw CameraException(
+        'Uninitialized CameraController',
+        'startImageStream was called on uninitialized CameraController.',
+      );
+    }
+    if (value.isRecordingVideo) {
+      throw CameraException(
+        'A video recording is already started.',
+        'startImageStream was called while a video is being recorded.',
+      );
+    }
+    if (value.isStreamingImages) {
+      throw CameraException(
+        'A camera has started streaming images.',
+        'startImageStream was called while a camera was streaming images.',
+      );
+    }
+
+    try {
+      await _channel.invokeMethod<void>('startImageStreamWithTorch');
+      value = value.copyWith(isStreamingImages: true);
+    } on PlatformException catch (e) {
+      throw CameraException(e.code, e.message);
+    }
+    const EventChannel cameraEventChannel =
+    EventChannel('plugins.flutter.io/camera/imageStream');
+    _imageStreamSubscription =
+        cameraEventChannel.receiveBroadcastStream().listen(
+              (dynamic imageData) {
+            onAvailable(CameraImage._fromPlatformData(imageData));
+          },
+        );
+  }
+
   /// Stop streaming images from platform camera.
   ///
   /// Throws a [CameraException] if image streaming was not started or video