Allow choosing camera on Xamarin form using Android Camera2 API

Emgu.CV.Example/XamarinForms/Core/Android/AndroidCameraManager.cs

@@ -21,6 +21,7 @@ using Android.Runtime;
 using Android.Util;
 using Android.Views;
 using Android.Widget;
+using Java.Security;
 using Paint = Android.Graphics.Paint;
 using Java.Util.Concurrent;
 using Xamarin.Forms.Platform.Android;
@@ -32,9 +33,16 @@ namespace Emgu.CV.XamarinForms
 {
     public class AndroidCameraManager
     {
+        public static String[] GetAvailableCameraIds()
+        {
+            CameraManager manager =
+                (CameraManager)Android.App.Application.Context.GetSystemService(Context.CameraService);
+            return manager.GetCameraIdList();
+        }
+        
         public EventHandler<Mat> OnImageCaptured;
 
-        public AndroidCameraManager(int? preferredPreviewSize = null)
+        public AndroidCameraManager(int? preferredPreviewSize = null, String preferedCameraId = null)
         {
             if (!SetUpCameraOutputs(preferredPreviewSize))
                 return;
@@ -54,11 +62,26 @@ namespace Emgu.CV.XamarinForms
 
                 var list = manager.GetCameraIdList();
                 var cameraId = list[0];
+                if (preferedCameraId != null)
+                {
+                    if (list.Contains(preferedCameraId))
+                    {
+                        cameraId = preferedCameraId;
+                    }
+                    else
+                    {
+                        throw new InvalidParameterException(
+                            String.Format("Camera ID '{0}' is not one of the available camera ids.", preferedCameraId));
+                    }
+                }
+                
                 backgroundHandler = _backgroundHandler;
 
                 // Attempt to open the camera. mStateCallback will be called on the background handler's
                 // thread when this succeeds or fails.
                 manager.OpenCamera(cameraId, _stateCallback, backgroundHandler);
+
+                _cameraId = cameraId;
             }
             catch (CameraAccessException e)
             {
@@ -133,7 +156,18 @@ namespace Emgu.CV.XamarinForms
         /// <summary>
         /// ID of the current {@link CameraDevice}.
         /// </summary>
-        string _cameraId;
+        private string _cameraId;
+
+        /// <summary>
+        /// Get the ID of the current {@link CameraDevice}.
+        /// </summary>
+        public String CurrentCameraId
+        {
+            get
+            {
+                return _cameraId;
+            }
+        }
 
         /// <summary>
         /// Return true if the given array contains the given integer.

Emgu.CV.Example/XamarinForms/Core/Android/AndroidCameraPage.cs

@@ -38,7 +38,7 @@ namespace Emgu.CV.XamarinForms
             
         }
 
-        public void StartCapture(EventHandler<Mat> matHandler, int preferredPreviewImageSize = -1)
+        public void StartCapture(EventHandler<Mat> matHandler, int preferredPreviewImageSize = -1, String preferedCameraId = null)
         {
             if (_cameraManager == null)
             {
@@ -49,7 +49,7 @@ namespace Emgu.CV.XamarinForms
                     preferredPreviewImageSize = Math.Max(preferredPreviewImageSize, 480 * 600);
                 }
 
-                _cameraManager = new AndroidCameraManager( preferredPreviewImageSize );
+                _cameraManager = new AndroidCameraManager( preferredPreviewImageSize, preferedCameraId );
                 _cameraManager.OnImageCaptured += matHandler;
                 _cameraManager.StartBackgroundThread();
             }

Emgu.CV.Example/XamarinForms/Core/Android/OnYuvImageAvailableListener.cs

@@ -45,10 +45,10 @@ namespace Emgu.CV.XamarinForms
                 using (GMat inYuvMat = new GMat())
                 using (GMat rgbMat = GapiInvoke.I4202BGR(inYuvMat))
                     //The following two step will rotate the image 90 degrees
-                using (GMat transposeMat = GapiInvoke.Transpose(rgbMat))
-                using (GMat rotatedMat = GapiInvoke.Flip(transposeMat, FlipType.Horizontal))
+                using (GMat tMat = GapiInvoke.Transpose(rgbMat))
+                using (GMat rMat = GapiInvoke.Flip(tMat, FlipType.Horizontal))
                 {
-                    _gComputation = new GComputation(inYuvMat, rotatedMat);
+                    _gComputation = new GComputation(inYuvMat, rMat);
                 }
             }
             else

Emgu.CV.Example/XamarinForms/Core/ButtonTextImagePage.cs

@@ -177,6 +177,10 @@ namespace Emgu.CV.XamarinForms
 
         public bool HasCameraOption { get; set; }
 
+#if __ANDROID__ && __USE_ANDROID_CAMERA2__
+        protected String _preferredCameraId = null;
+#endif
+
         public virtual async Task<Mat[]> LoadImages(String[] imageNames, String[] labels = null)
         {
             Mat[] mats = new Mat[imageNames.Length];
@@ -216,7 +220,16 @@ namespace Emgu.CV.XamarinForms
                         || Device.RuntimePlatform == Device.UWP)
                     {
                         if (captureSupported)
+                        {
+#if __ANDROID__ && __USE_ANDROID_CAMERA2__
+                            foreach (String cameraId in AndroidCameraManager.GetAvailableCameraIds())
+                            {
+                                options.Add(String.Format("Camera {0}", cameraId));
+                            }
+#else
                             options.Add("Camera");
+#endif
+                        }
                     }
                     else if (Device.RuntimePlatform == Device.WPF
                           || Device.RuntimePlatform == Device.macOS)
@@ -224,7 +237,9 @@ namespace Emgu.CV.XamarinForms
                         var openCVConfigDict = CvInvoke.ConfigDict;
                         bool haveVideoio = (openCVConfigDict["HAVE_OPENCV_VIDEOIO"] != 0);
                         if (haveVideoio)
+                        {
                             options.Add("Camera");
+                        }
                     }
                 }
 
@@ -287,9 +302,21 @@ namespace Emgu.CV.XamarinForms
                     using (Stream stream = await takePhotoResult.OpenReadAsync())
                         mats[i] = await ReadStream(stream);
                 }
-                else if (action.Equals("Camera"))
+                else if (action.StartsWith("Camera"))
                 {
                     mats = Array.Empty<Mat>();
+                    
+#if __ANDROID__ && __USE_ANDROID_CAMERA2__
+                    String cameraIdCandidate = action.Replace("Camera ", "");
+                    if (AndroidCameraManager.GetAvailableCameraIds().Contains(cameraIdCandidate))
+                    {
+                        _preferredCameraId = cameraIdCandidate;
+                    }
+                    else
+                    {
+                        _preferredCameraId = null;
+                    }
+#endif
                 }
             }
 

Emgu.CV.Example/XamarinForms/Core/ProcessAndRenderPage.cs

@@ -291,36 +291,40 @@ namespace Emgu.CV.XamarinForms
             {
 #if __ANDROID__ && __USE_ANDROID_CAMERA2__
                
-                StartCapture(async delegate (Object captureSender, Mat m)
-                {
-                    //Skip the frame if busy, 
-                    //Otherwise too many frames arriving and will eventually saturated the memory.
-                    if (!_isBusy)
+                StartCapture(
+                    async delegate (Object captureSender, Mat m)
                     {
-                        _isBusy = true;
-                        try
+                        //Skip the frame if busy, 
+                        //Otherwise too many frames arriving and will eventually saturated the memory.
+                        if (!_isBusy)
                         {
-                            String message = String.Empty;
-                            await Task.Run(() => 
+                            _isBusy = true;
+                            try
                             {
-                                if (_renderMat == null)
-                                    _renderMat = new Mat();
-                                using (InputArray iaImage = m.GetInputArray())
+                                String message = String.Empty;
+                                await Task.Run(() => 
                                 {
-                                    iaImage.CopyTo(_renderMat);
-                                }
-                                message = _model.ProcessAndRender(m, _renderMat);
-                            });
-                            SetImage(_renderMat);
-                            SetMessage(message);
-
-                        }
-                        finally
-                        {
-                            _isBusy = false;
+                                    if (_renderMat == null)
+                                        _renderMat = new Mat();
+                                    using (InputArray iaImage = m.GetInputArray())
+                                    {
+                                        iaImage.CopyTo(_renderMat);
+                                    }
+                                    message = _model.ProcessAndRender(m, _renderMat);
+                                });
+                                SetImage(_renderMat);
+                                SetMessage(message);
+
+                            }
+                            finally
+                            {
+                                _isBusy = false;
+                            }
                         }
-                    }
-                });
+                    },
+                    -1,
+                    this._preferredCameraId
+                    );
 #elif __IOS__
                 CheckVideoPermissionAndStart ();
 #else