Fill: SelectCommand.Connection 属性尚未初始化。求救啊，弄了好久啊

Question

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Data.SqlClient;public partial class teacher : System.Web.UI.Page
{
    SqlConnection sms_conn;
    string sms_sqlstr, sms_sqlstr2;
    protected void Page_Load(object sender, EventArgs e)
    {        string sms_connstr = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        sms_conn = new SqlConnection(sms_connstr);
        if (!Page.IsPostBack)
            SMS_BindGrid();
        
    }
    void SMS_BindGrid()
    {
        //SqlDataAdapter sms_da = new SqlDataAdapter("select teacherid,teachername,department.departmentid,department.departmentname,sex,telephone from teacher,department where teacher.departmentid=department.departmentid", sms_conn);
        //DataSet sms_ds = new DataSet();
        //sms_da.Fill(sms_ds, "T");
        //sms_teacher.DataSource = sms_ds.Tables["T"].DefaultView;
        //sms_teacher.DataBind();        //SqlDataAdapter sms_da2 = new SqlDataAdapter("select * from department", sms_conn);
        //DataSet sms_ds2 = new DataSet();
        //sms_da2.Fill(sms_ds2, "T");
        //DropDownList1.DataSource = sms_ds2.Tables["T"].DefaultView;
        //DropDownList1.DataTextField = "departmentname";
        //DropDownList1.DataValueField = "departmentname";
        //DropDownList1.DataBind();        sms_sqlstr = "select teacherid,teachername,department.departmentid,department.departmentname,sex,telephone from teacher,department where teacher.departmentid=department.departmentid";
        SqlDataAdapter sms_da = new SqlDataAdapter(sms_sqlstr, sms_conn);
        DataSet sms_ds = new DataSet();
        sms_da.Fill(sms_ds, "T");
        sms_teacher.DataSource = sms_ds;
        sms_teacher.DataBind();        sms_sqlstr2 = "select * from department";
        SqlDataAdapter sms_da2 = new SqlDataAdapter(sms_sqlstr2, sms_conn);
        DataSet sms_ds2 = new DataSet();
        sms_da2.Fill(sms_ds2, "T");
        DropDownList1.DataSource = sms_ds2.Tables["T"];
        DropDownList1.DataTextField = "departmentname";
        DropDownList1.DataValueField = "departmentname";
        DropDownList1.DataBind();    }
        protected void sms_teacher_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        sms_teacher.PageIndex = e.NewPageIndex;
        SMS_BindGrid();
    }   
    protected void GridView_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        sms_teacher.EditIndex = -1;
        SMS_BindGrid();    }    protected void GridView_RowDeleting(object sender, GridViewDeleteEventArgs e)
    {
       
        string sms_aqlstr = "delete from teacher where Teacherid=@teacher_id";
        SqlCommand sms_comm = new SqlCommand(sms_aqlstr,sms_conn);
        sms_comm.Parameters.AddWithValue("@teacher_id",sms_teacher.DataKeys[e.RowIndex].Value.ToString());
        sms_comm.Parameters.Add(new SqlParameter("@teacher_id", SqlDbType.Char, 8));
        sms_comm.Parameters["@teacher_id"].Value = sms_teacher.DataKeys[(int)e.RowIndex].ToString();
        sms_comm.Connection.Open();
        try
        {
            sms_comm.ExecuteNonQuery();
            sms_lbl_note.Text = "删除成功";
        }
        catch (Exception ex)
        {
            sms_lbl_note.Text = "删除失败" + ex.Message;        }
        finally
        {            sms_comm.Connection.Close();
            sms_conn = null;
            sms_comm = null;
            sms_teacher.EditIndex = -1;
            SMS_BindGrid();
        }    }    protected void GridView_RowEditing(object sender, GridViewEditEventArgs e)
    {
        sms_teacher.EditIndex = e.NewEditIndex;
        SMS_BindGrid();
    }
    protected void GridView_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {    }    protected void Button1_Click(object sender, EventArgs e)
    {
       
        SqlCommand sms_comm = new SqlCommand("Employess_Sel",sms_conn);
        sms_comm.CommandType = CommandType.StoredProcedure;
        sms_comm.CommandText = "Employess_Sel";
        sms_comm.Connection = sms_conn;
        SqlDataAdapter sms_da = new SqlDataAdapter(sms_comm);
        //sms_da.SelectCommand = new SqlCommand("Employess_Sel",sms_conn);
        sms_da.SelectCommand = sms_comm;
        sms_da.SelectCommand.Parameters.Add("@lastname",SqlDbType.NVarChar);
        sms_da.SelectCommand.Parameters.Add("@department", SqlDbType.VarChar,30);
        sms_da.SelectCommand.Parameters["@lastname"].Value = this.TextBox1.Text.Trim().Replace("'","''");
        sms_da.SelectCommand.Parameters["@department"].Value = this.DropDownList1.SelectedValue.ToString(); ;
        DataSet sms_ds = new DataSet();
        sms_da.Fill(sms_ds);
        sms_teacher.DataSource = sms_ds;
        sms_teacher.DataBind();
    }
}

Answer 1

除Page_Load外，每个方法里执行开头都要加上：
if(sms_conn.State==ConnectionState.Closed)
    sms_conn.Open();
保证数据连接打开，再执行数据库操作。

Answer 2

SelectCommand.Connection 属性尚未初始化
说明你new出SqlDataAdapter时给你指定的Connection为null，你检查一下。
另外你把finally代码中sms_conn = null;删去。

Answer 3

删除失败变量名 '@teacher_id' 已声明。变量名在查询批次或存储过程内部必须唯一。 
出现这个问题了

Answer 4

sms_sqlstr = "select teacherid,teachername,department.departmentid,department.departmentname,sex,telephone from teacher,department where teacher.departmentid=department.departmentid";
  SqlDataAdapter sms_da = new SqlDataAdapter(sms_sqlstr, sms_conn);
  DataSet sms_ds = new DataSet();
  sms_da.Fill(sms_ds, "T");  sms_teacher.DataSource = sms_ds;
  sms_teacher.DataBind();这句出现问题哦

Answer 5

sms_comm.Parameters.AddWithValue("@teacher_id",sms_teacher.DataKeys[e.RowIndex].Value.ToString());
请问大侠这句有没有错哦