Use a library Google Vision. When I open the text reading window, I can't turn on the flash at all to improve the quality of the image in the dark.

What is the method used to turn on the flash when reading texts??

i read this but nothing

https://stackoverflow.com/questions/35811411/accessing-autofocus-flash-with-google-vision-barcode-reader

all code //

  protected override void OnCreate(Bundle savedInstanceState)
            base.OnCreate(savedInstanceState);
            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);
            cameraView = FindViewById<SurfaceView>(Resource.Id.surface_view);
            txtView = FindViewById<TextView>(Resource.Id.txtview);
            TextRecognizer txtRecognizer = new TextRecognizer.Builder(ApplicationContext).Build();
            if (!txtRecognizer.IsOperational)
                Log.Error("Main Activity", "Detector dependencies are not yet available");
                cameraSource = new CameraSource.Builder(ApplicationContext, txtRecognizer)
                    .SetFacing(CameraFacing.Back)
                    .SetRequestedPreviewSize(1280, 1024)
                    .SetRequestedFps(2.0f)
                    .SetAutoFocusEnabled(true)
                    .Build();
                cameraView.Holder.AddCallback(this);
                txtRecognizer.SetProcessor(this);
        public void SurfaceChanged(ISurfaceHolder holder, [GeneratedEnum] Format format, int width, int height)
        public void SurfaceCreated(ISurfaceHolder holder)
            if (ActivityCompat.CheckSelfPermission(ApplicationContext, Manifest.Permission.Camera) != Android.Content.PM.Permission.Granted)
                //Request permission
                ActivityCompat.RequestPermissions(this, new string[] {
                    Android.Manifest.Permission.Camera
                }, RequestCameraPermissionID);
                return;
            cameraSource.Start(cameraView.Holder);
        public void SurfaceDestroyed(ISurfaceHolder holder)
            cameraSource.Stop();
						
Hello,​    
Welcome to our Microsoft Q&A platform!    
Flashlight is not include in the Xamarin.GooglePlayServices.Vision API, Google implemented those features (CameraSource.Builder) in native android CameraSource.Builder setFlashMode.    
This feature request is opened like this thread: Support getCamera() instance in CameraSource.    
Here is two ways to enable the flash mode.    
 Download this native android library from Google, binding this library. Here's a good article on how to get started: Binding a Java Library.    
  Using Reflection. You can get the Camera Object from CameraSouce and add the flash parameter then set the updated parameters to the camera.           private void Button1_Click(object sender, System.EventArgs e)  

                 //call it to open the Flash   

                   setFlash(true);  

      public Android.Hardware.Camera getCameraObject(CameraSource _camSource)  
          Field[] cFields = _camSource.Class.GetDeclaredFields();  
          Android.Hardware.Camera _cam = null;  
              foreach (Field item in cFields)  
                  if (item.Type.CanonicalName == "android.hardware.Camera")  
                      Console.WriteLine("Camera");  
                      item.Accessible = true;  
                          _cam = (Android.Hardware.Camera)item.Get(_camSource);  
                      catch (Exception e)  
          catch (Exception e)  
          return _cam;  
      bool isTorch;  
      public void setFlash(bool isEnable)  
              isTorch = !isEnable;  
              Android.Hardware.Camera _cam = getCameraObject(mCameraSource);  
              if (_cam == null) return;  
              var _pareMeters = _cam.GetParameters();  
              var _listOfSuppo = _cam.GetParameters().SupportedFlashModes;  
              _pareMeters.FlashMode = isTorch ? _listOfSuppo[0] : _listOfSuppo[3];  
              _cam.SetParameters(_pareMeters);  
          catch (Exception e)  
And do not forget to add android.permission.FLASHLIGHT permission in the AndroidManifest.xml.    
Best Regards,    
Leon Lu    
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