ASP.NET实现动态二级下拉框(非js版本)

此下拉框是使用.net控件的下拉框，后台实现数据库访问，用了ajax控件来实现局部刷新，如不需要可以不用。

其中实现下拉框的选定事件OnSelectedIndexChanged()是关键，添加此事件的必须将AutoPostBack设为true。

页面文件.aspx

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:DropDownList ID="ddlBranch_Root" runat="server" OnSelectedIndexChanged="ddlBranch_Root_SelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>
<asp:DropDownList ID="ddlBranch_Leaf" runat="server" Visible="false"></asp:DropDownList>
</ContentTemplate>
</asp:UpdatePanel>

后台文件.cs

  protected void ddlBranch_Root_SelectedIndexChanged(object sender, EventArgs e)
    {   //一级下拉框的选定值
        int RootCPID = int.Parse(ddlBranch_Root.SelectedValue);
        if(RootCPID != 999)
        {//如果选定值不等于999，这里设定“请选择”此Item项值是999
            IList<CPBranch> LeafBranch = CPBranchBLL.GetByParentID(RootCPID);//读数据库，取出二级下拉框的项
            if (LeafBranch.Count > 0)
            {   //如果一级下拉框的选定项有子项目，则显示二级下拉框
                ddlBranch_Leaf.Visible = true;
                
                ListItemCollection LeafBranchList = new ListItemCollection();
                for (int i = 0; i < LeafBranch.Count; i++)
                {
                    ListItem temp = new ListItem();
                    temp.Value = LeafBranch[i].ID.ToString();
                    temp.Text = LeafBranch[i].Name;
                    LeafBranchList.Add(temp);

                }
                ddlBranch_Leaf.DataSource = LeafBranchList;
                ddlBranch_Leaf.DataValueField = "value";
                ddlBranch_Leaf.DataTextField = "text";
                ddlBranch_Leaf.DataBind();//绑定数据源
            }
            else ddlBranch_Leaf.Visible = false;//如果一级下拉框的选定项无子项目，则不显示二级下拉框
        }
    }