void UseFaceDetectionModel() { var faceDetector = vision.GetFaceDetector(); var image = new VisionImage(ImgSample.Image); faceDetector.ProcessImage(image, HandleVisionFaceDetectionCallback); void HandleVisionFaceDetectionCallback(VisionFace [] faces, NSError error) { if (error != null) { TxtData.Text = error.Description; return; } if (faces == null || faces.Length == 0) { TxtData.Text = "No faces were found."; return; } var imageSize = ImgSample.Image.Size; UIGraphics.BeginImageContextWithOptions(imageSize, false, 0); var context = UIGraphics.GetCurrentContext(); context.SetStrokeColor(UIColor.Red.CGColor); context.SetLineWidth(10); ImgSample.Image.Draw(CGPoint.Empty); foreach (var face in faces) { context.AddRect(face.Frame); context.DrawPath(CGPathDrawingMode.Stroke); } var newImage = UIGraphics.GetImageFromCurrentImageContext(); UIGraphics.EndImageContext(); ImgSample.Image = newImage; } }