关于下拉列表的求救

Question

for (int i = 0; i < NavigateTree.InfinityTree.Rows.Count; i++)
        {
            ClassDrop.Items.Add(NavigateTree.InfinityTree.Rows[i]["StrTree"].ToString());
            ClassDrop.Items[i].Value = NavigateTree.InfinityTree.Rows[i]["Classid"].ToString();
        }
        ClassDrop.Items.Insert(0, "一级分类");
        ClassDrop.Items[0].Value = "0"; Connection = new OleDbConnection(DataProvider.ConnectionString);
            Command = new OleDbCommand();
            Command.Connection = Connection;
            Command.CommandText = "Select * From aClass where Classid=" + ClassDrop.SelectedValue;
            Connection.Open();
            dr= Command.ExecuteReader();为什么ClassDrop.SelectedValue选出来的为空??

Answer 1

for (int i = 0; i  < NavigateTree.InfinityTree.Rows.Count; i++) 
        { 
            ClassDrop.Items.Add(NavigateTree.InfinityTree.Rows[i]["StrTree"].ToString()); 
            ClassDrop.Items[i].Value = NavigateTree.InfinityTree.Rows[i]["Classid"].ToString(); 
        } 
        ClassDrop.Items.Insert(0, "一级分类"); 
        ClassDrop.Items[0].Value = "0"; 
===========================================
只往里添加了。也没有选择阿另外，添加的时候value和text为什么要分开呢ListItem itm=new ListItem(value,text);
ClassDrop.Items.Add(itm);

Answer 2

tryprivate void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostBack)
{
                             你的绑定程序
                        }

Answer 3

2005里面,可以直接ClassDrop.text.tostring()

Answer 4

lican990602 正解
应该是这原因，绑定dropdownlist的代码写在if(!IsPostBack){}里面，不能每次都绑，不然每次刷新就又回去了，

Answer 5

dropdownlist的装载信息是写在if(!page.ispostback)里面的,我也用了ClassDrop.SelectedValue.tostring()和ClassDrop.text.tostring()都显示的还是空值.