How to export chart to PDF in Xamarin.iOS

ExportToPDF.TouchDown += (object sender, EventArgs e) =>
   {
       MemoryStream stream = new MemoryStream();
       ConvertToPDF("Sfchart.pdf", stream, chart);
   };

public void ConvertToPDF(string filename, MemoryStream stream, SFChart nativechart)
 {
            PdfDocument doc = new PdfDocument();
            doc.PageSettings.Margins.All = 0;
            PdfPage page = doc.Pages.Add();
            PdfGraphics g = page.Graphics;
 
            UIGraphics.BeginImageContext(nativechart.Frame.Size);
            nativechart.Layer.RenderInContext(UIGraphics.GetCurrentContext());
 
            UIImage image = UIGraphics.GetImageFromCurrentImageContext();
            UIGraphics.EndImageContext();
 
            Stream imgStream = image.AsJPEG().AsStream();
            g.DrawImage(PdfImage.FromStream(imgStream), 30, 30, 500, 700);
 
            doc.Save(stream);
            doc.Close(true);
 
            string path = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
            string filePath = Path.Combine(path, filename);
 
            try
            {
                FileStream fileStream = File.Open(filePath, FileMode.Create);
                stream.Position = 0;
                stream.CopyTo(fileStream);
                fileStream.Flush();
                fileStream.Close();
            }
            catch (Exception e)
            {
                e.Message.ToString();
            }
 
            UIViewController currentController = UIApplication.SharedApplication.KeyWindow.RootViewController;
 
            while (currentController.PresentedViewController != null)
                currentController = currentController.PresentedViewController;
            
            QLPreviewController qlPreview = new QLPreviewController();
            QLPreviewItem item = new QLPreviewItemBundle(filename, filePath);
            qlPreview.DataSource = new PreviewControllerDS(item);
 
            currentController.PresentViewController((UIViewController)qlPreview, true, (Action)null);
        }
}

public class QLPreviewItemFileSystem : QLPreviewItem
 {
        string _fileName, _filePath;
 
        public QLPreviewItemFileSystem(string fileName, string filePath)
        {
            _fileName = fileName;
            _filePath = filePath;
        }
 
        public override string ItemTitle
        {
            get
            {
                return _fileName;
            }
        }
 
        public override NSUrl ItemUrl
        {
            get
            {
                return NSUrl.FromFilename(_filePath);
            }
        }
    }
 
    public class QLPreviewItemBundle : QLPreviewItem
    {
        string _fileName, _filePath;
        public QLPreviewItemBundle(string fileName, string filePath)
        {
            _fileName = fileName;
            _filePath = filePath;
        }
 
        public override string ItemTitle
        {
            get
            {
                return _fileName;
            }
        }
        public override NSUrl ItemUrl
        {
            get
            {
                var documents = NSBundle.MainBundle.BundlePath;
                var lib = Path.Combine(documents, _filePath);
                var url = NSUrl.FromFilename(lib);
                return url;
            }
        }
    }
 
    public class PreviewControllerDS : QLPreviewControllerDataSource
    {
        private QLPreviewItem _item;
 
        public PreviewControllerDS(QLPreviewItem item)
        {
            _item = item;
        }
 
        public override nint PreviewItemCount(QLPreviewController controller)
        {
            return (nint)1;
        }
 
        public override IQLPreviewItem GetPreviewItem(QLPreviewController controller, nint index)
        {
            return _item as IQLPreviewItem;
        }
    }