How to export the charts in Xamarin.Android

public void SaveAsImage(string filename) 
{ 
    // create bitmap screen capture
    chart.DrawingCacheEnabled = true; 
   // view will save its state
    chart.SaveEnabled = true; 
    Bitmap bitmap = null; 
 
    using (bitmap = chart.DrawingCache) 
    { 
        var extension = filename.Split('.'); 
 
       // create an image path with existing environment with the provided file name without having the extension
 
        var imagePath = 
            new Java.IO.File(Android.OS.Environment.ExternalStorageDirectory + "/Pictures/" + filename); 
 
        imagePath.CreateNewFile(); 
        using (Stream fileStream = new FileStream(imagePath.AbsolutePath, System.IO.FileMode.OpenOrCreate)) 
        { 
            try 
            { 
               //Compressed bitmap to get needed format
                string imageExtension = extension.Length > 1 ? extension[1].Trim().ToLower() : "jpg"; 
                switch (imageExtension) 
                { 
                    case "png": 
                        bitmap.Compress(Bitmap.CompressFormat.Png, 100, fileStream); 
                        break; 
                    case "jpg":  case "jpeg": default: 
                        bitmap.Compress(Bitmap.CompressFormat.Jpeg, 100, fileStream); 
                        break; 
                } 
            } 
            finally 
            { 
              //Closing stream and disabled drawing cache.
                fileStream.Flush(); 
                fileStream.Close(); 
                chart.DrawingCacheEnabled = false; 
            } 
        } 
    } 
} 

<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
          android:versionCode="1" 
          android:versionName="1.0" 
          package="ExportChartAsImage.ExportChartAsImage">
 
          …
 
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
</manifest>