ListBox1.SelectedItem 为NULL

Question

ListBox1控件在页面上显示是有数据的！但在后台就是为NULL
 public void dropForListBox()
    {
        if (DropDownList1.SelectedIndex.Equals(0))
        {
            SqlConnection con = new SqlConnection("server=gea-server;database=cqscada;uid=sa;pwd=;");
            con.Open();
            SqlDataAdapter sda = new SqlDataAdapter("select * from 变电站", con);
            DataSet ds = new DataSet();
            sda.Fill(ds, "变电站");
            //this.ListBox1.SelectedIndex
            this.ListBox1.DataSource = ds.Tables["变电站"];
            this.ListBox1.DataTextField = "站名称";
            this.ListBox1.DataValueField = "局编号";
            this.ListBox1.DataBind();
            con.Close();
        }
        else
        {
            if (DropDownList1.SelectedIndex.Equals(1))
            {
                SqlConnection con = new SqlConnection("server=gea-server;database=cqscada;uid=sa;pwd=;");
                con.Open();
                SqlDataAdapter sda = new SqlDataAdapter("select * from 开闭所", con);
                DataSet ds = new DataSet();
                sda.Fill(ds, "开闭所");
                this.ListBox1.DataSource = ds.Tables["开闭所"];
                this.ListBox1.DataTextField = "开闭所名称";
                this.ListBox1.DataValueField = "开闭所序号";
                this.ListBox1.DataBind();
                con.Close();
            }
            else
            {
                if (DropDownList1.SelectedIndex.Equals(2))
                {
                    SqlConnection con = new SqlConnection("server=gea-server;database=cqscada;uid=sa;pwd=;");
                    con.Open();
                    SqlDataAdapter sda = new SqlDataAdapter("select * from 馈线", con);
                    DataSet ds = new DataSet();
                    sda.Fill(ds, "馈线");
                    this.ListBox1.DataSource = ds.Tables["馈线"];
                    this.ListBox1.DataTextField = "馈线名称";
                    this.ListBox1.DataValueField = "馈线序号";
                    this.ListBox1.DataBind();
                    con.Close();
                }            }
        }
    }    protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        dropForListBox();
        Response.Write(ListBox1.SelectedItem);
        if (this.RadioButton1.Checked)
        {
            SqlConnection con = new SqlConnection("server=gea-server;database=cqscada;uid=sa;pwd=;");
            con.Open();
            SqlDataAdapter sda = new SqlDataAdapter("select  站名称 as 名称 from 变电站 where 站名称 ='"+this.ListBox1.SelectedValue+"'", con);
            DataSet ds = new DataSet();
            sda.Fill(ds, "变电站");
            this.GridView1.DataSource = ds;
            this.GridView1.DataBind();
            con.Close();
        }
        else 
        {
            if (this.RadioButton2.Checked)
            {
                SqlConnection con = new SqlConnection("server=gea-server;database=cqscada;uid=sa;pwd=;");
                con.Open();
                SqlDataAdapter sda = new SqlDataAdapter("select  站名称 as 名称 from 变电站", con);
                DataSet ds = new DataSet();
                sda.Fill(ds, "变电站");
                this.GridView1.DataSource = ds;
                this.GridView1.DataBind();
                con.Close();
            }
            else
            {
                if (this.RadioButton3.Checked)
                {
                    SqlConnection con = new SqlConnection("server=gea-server;database=cqscada;uid=sa;pwd=;");
                    con.Open();
                    SqlDataAdapter sda = new SqlDataAdapter("select  站名称 as 名称 from 变电站", con);
                    DataSet ds = new DataSet();
                    sda.Fill(ds, "变电站");
                    this.GridView1.DataSource = ds;
                    this.GridView1.DataBind();
                    con.Close();
                }
            }
           
        }
            }

Answer 1

試試用foreach ds.Tables["开闭所"]來添加到listbox裡同去 

Answer 2

楼主，应该是网页回发引起的。后台代码:  1   page_onload 时： If(!IsPostBack) { //填充DropDownList     dropForListBox();   }
          2   protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e) 时：把dropForListBox()代码屏蔽掉。 

Answer 3

楼主，应该是网页回发引起的。后台代码:  1  page_onload 时： If(!IsPostBack) { //填充DropDownList    dropForListBox();  }
          2  protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e) 时：把dropForListBox()代码屏蔽掉。这样是ListBox1.SelectedValue和ListBox1.SelectedItem有了！但是又出现了个新的问题！ListBox1的ListBox1_SelectedIndexChanged事件只触发一次！觉得很奇怪，我AutoPostback= true了！但当我选ListBox1的一个Item后换成别的Item就是不触发ListBox1_SelectedIndexChanged事件！也就是 GridView1控件不刷新