public static DataTable GetDataTable(this GridView view)
{
    DataTable dt = new DataTable();
    foreach (GridColumn c in view.Columns)
        dt.Columns.Add(c.FieldName, c.ColumnType);
    for (int r = 0; r < view.RowCount; r++)
    {
        object[] rowValues = new object[dt.Columns.Count];
        for (int c = 0; c < dt.Columns.Count; c++)
            rowValues[c] = view.GetRowCellValue(r, dt.Columns[c].ColumnName);
        dt.Rows.Add(rowValues);
    }
    return dt;
}

//Call function
DataTable dt = grdView.GetDataTable();