How to copy cell value instead of formula in WinRT Spreadsheet?

public class CustomCopyPaste : SpreadsheetCopyPaste
{
  public SfSpreadsheet spreadSheet
  {
    get;
    set;
  }
  public CustomCopyPaste(SfSpreadsheet spread)
            : base()
  {
     spreadSheet = spread;
  }
  public override void Copy()
  {
    var copyRange = spreadSheet.ActiveGrid.SelectedRanges.ActiveRange;
    var excelSourceRange = copyRange.ConvertGridRangeToExcelRange(spreadSheet.ActiveGrid);
    SourceWorkbookRange = spreadSheet.ActiveGrid.Worksheet.Range[excelSourceRange];
    CopyClipboard(copyRange);
    SourceGrid = spreadSheet.ActiveGrid;
  }
 
   public void CopyClipboard(GridRangeInfo copyRange)
   {
            var sb = new StringBuilder();
 
            for (int i = copyRange.Top; i <= copyRange.Bottom; i++)
            {
                for (int j = copyRange.Left; j <= copyRange.Right; j++)
                {
 
                    sb.Append(SourceWorkbookRange[i, j].DisplayText);
                    if (j != copyRange.Right)
                        sb.Append("\t");
                }
                if (i != copyRange.Bottom)
                    sb.Append("\r\n");
            }
 
            var data = new DataObject();
 
            if (sb.Length == 0)
            {
                sb.Append(" ");
            }
 
 
            data.SetText(sb.ToString());
 
            Clipboard.SetDataObject(data);
 
            sb.Clear();
   }
}