selectedindexchanged event not firing

Question

我有三个dropdownlists与autopostaback=true，但问题是，对于第二个dropdownlist只有pageload被称为但它的selectedindexchanged不射击！我能做些什么？（dropdownlists在updatepanel）

EDIT: 
protected void Page_Load(object sender, EventArgs e) 
    { 
     if (DDL_d1.Items.Count == 0) 
     { 
      SqlDataReader dr = null; 
      DbAccessor db = new DbAccessor(); 
      dr = db.SqlSelectS("true", "SELECT Fname FROM [Tbl_Amoozesh]"); 
      DDL_d1.Items.Clear(); 
      while (dr.Read()) 
       DDL_d1.Items.Add(dr[0].ToString()); 
      db.Dispose(); 
     } 
    } 
    protected void d1(object sender, EventArgs e) 
    { 

     DDL_d1.AutoPostBack = false; 
     SqlDataReader dr = null; 
     DbAccessor db = new DbAccessor(); 
     dr = db.SqlSelectS(DDL_d1.SelectedValue,"SELECT Fname FROM [Tbl_Amoozesh] where Fname = @a"); 
     DDL_d2.Items.Clear(); 
     DDL_d2.Items.Add(new ListItem("hi")); 
     while (dr.Read()) 
      DDL_d2.Items.Add(dr[0].ToString()); 
     db.Dispose(); 




    } 
    protected void d2(object sender, EventArgs e) 
    { 

     SqlDataReader dr = null; 
     DbAccessor db = new DbAccessor(); 
     dr = db.SqlSelectS(DDL_d2.SelectedValue, "SELECT Lname FROM [Tbl_Amoozesh] where Fname = @a"); 
     DDL_d3.Items.Clear(); 
     while (dr.Read()) 
      DDL_d3.Items.Add(dr[0].ToString()); 
     db.Dispose(); 

    } 

Answer 1

你必须把异步触发你的UpdatePanel。试试这个：

<asp:UpdatePanel id="up1" runat="server" updatemode="conditional"> 
    <Triggers> 
     <asp:AsyncPostBackTrigger ControlID="ddl" EventName="SelectedIndexChanged" /> 
    </Triggers> 
    <ContentTemplate> 
     <%-- your content here --%> 
     <asp:DropdownList id="ddl" AutoPostback="true" OnSelectedIndexChanged="handler" /> 
    </ContentTemplate> 
</asp:UpdatePanel>