大家快来帮小弟我看看这段代码 dropdownlist绑定 无数据显示 C# .net

大家快来帮我看看这段代码 dropdownlist绑定 无数据显示 C# .net
SqlConnection sqlcon = new SqlConnection();
 string connstr = @"Data Source=.\SQLEXPRESS;AttachDBFilename=|DataDirectory|\xiangdan.mdf;Integrated Security=True;User Instance=True";
  sqlcon.ConnectionString = connstr;

  SqlCommand cmd = new SqlCommand();
  cmd.Connection = sqlcon;
  cmd.CommandText = "select*from xiangdan";

  SqlDataAdapter adapter = new SqlDataAdapter();
  adapter.SelectCommand = cmd;

  DataSet bown = new DataSet();
  adapter.Fill(bown);

  DataTable dt = bown.Tables["xiangdan"];
  DropDownList1.DataSource = dt;
  DropDownList1.SelectedValue = "nianji";
   
  DropDownList1.DataValueField = "xueyuan";
  DropDownList1.DataTextField = "banji"; 
  DropDownList1.DataBind();
  Response.Write("this.DropDownList1.DataTextField = 'banji'");

[解决办法]

C# code

string connstr = @"Data Source=.\SQLEXPRESS;AttachDBFilename=|DataDirectory|\xiangdan.mdf;Integrated Security=True;User Instance=True";DataSet bown = new DataSet();using(SqlConnection sqlcon = new SqlConnection(connstr)){      string strSQL = "select * from xiangdan";      using(SqlDataAdapter adapter = new SqlDataAdapter(strSQL,sqlcon))     {           adapter.Fill(bown);           DropDownList1.DataSource = bown;           DropDownList1.DataTextField = "banji";            DropDownList1.DataValueField = "xueyuan";           DropDownList1.DataBind();           // DropDownList1.SelectedValue = "nianji";     }}