将DataTable写入csv代码中断for循环

Question

我想在for循环中写一个DataTable 但是，写入步骤似乎打破了for循环。 for循环只运行一次。

如何在不中断for循环的情况下从.csv编写DataTable文件？

for (i=0;i<10;i++)
{
    StringBuilder sb = new StringBuilder();

    IEnumerable<string> columnNames = listDataTable[dtIndex].Columns.Cast<DataColumn>().
                                      Select(column => column.ColumnName);
    sb.AppendLine(string.Join(",", columnNames));

    foreach (DataRow row in listDataTable[dtIndex].Rows)
    {
        IEnumerable<string> fields = row.ItemArray.Select(field => field.ToString());
        sb.AppendLine(string.Join(",", fields));
    }

    File.WriteAllText("test.csv", sb.ToString());
}