SQL下拉列表C#表单ASP.NET未填充

using System;
using System.Data;
using System.Data.SqlClient;
using System.Web.UI.WebControls;

public partial class YourPage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            // 建立与数据库的连接
            string connectionString = "YourConnectionString";
            SqlConnection connection = new SqlConnection(connectionString);

            // 编写SQL查询语句
            string query = "SELECT ColumnName FROM TableName";

            // 执行查询
            SqlCommand command = new SqlCommand(query, connection);
            connection.Open();
            SqlDataReader reader = command.ExecuteReader();

            // 填充下拉列表
            if (reader.HasRows)
            {
                while (reader.Read())
                {
                    string value = reader.GetString(0);
                    DropDownList1.Items.Add(value);
                }
            }

            reader.Close();
            connection.Close();
        }
    }
}