asp.net-使用Streamwriter打开文件保存弹出窗口

Question

以下代码可以正常工作，并将结果导出到D驱动器中提到的文件中。我们如何更改它以便打开POPUP并询问将文件保存在何处

受保护的无效Button1_Click（对象发送者，EventArgs e）     {

    using (StreamWriter writer = new StreamWriter("D:\\dump.csv"))
    {
        WriteDataTable(dt, writer, true);
    }

}

public static void WriteDataTable(DataTable sourceTable, TextWriter writer, bool includeHeaders)
{
    if (includeHeaders)
    {
        IEnumerable<String> headerValues = sourceTable.Columns
            .OfType<DataColumn>()
            .Select(column => QuoteValue(column.ColumnName));

        writer.WriteLine(String.Join(",", headerValues));
    }

    IEnumerable<String> items = null;

    foreach (DataRow row in sourceTable.Rows)
    {
        items = row.ItemArray.Select(o => QuoteValue(o?.ToString() ?? String.Empty));
        writer.WriteLine(String.Join(",", items));
    }

    writer.Flush();
}

private static string QuoteValue(string value)
{
    return String.Concat("\"",
    value.Replace("\"", "\"\""), "\"");
}