在ASP .Net中的第一个PostBack之后，Update Panel中的下拉列表不起作用

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问题描述

嗨亲爱的

我在更新面板中有3个下拉列表。

国家，州，地区。这3个下拉列表是相关的。

如果我从国家/地区下拉列表中选择国家/地区名称，则所选国家/地区的所有州都将在州下拉列表中可用。它只适用于第一次回发...

状态下拉列表并不令所有回发更新，除了第一次回发..

我使用了

Hi Dears

I have 3 dropdown lists inside an Update Panel.
Country,State,Area respectively. These 3 Dropdowns are related.

If I choose a Country Name from the Country dropdown then all the states of selected country will be available in state dropdown . It works fine for first postback only...
the state dropdown is not refreshing for all postback except the first postback..

I have used

<Triggers>
           <asp:AsyncPostBackTrigger ControlID="ddlCountry"  EventName="SelectedIndexChanged"/>
<asp:AsyncPostBackTrigger ControlID="ddlState"  EventName="SelectedIndexChanged"/>
<asp:AsyncPostBackTrigger ControlID="ddlArea"  EventName="SelectedIndexChanged"/></Triggers>

仍然没有刷新第二次回发的状态下拉菜单..

如果有人对此有任何想法，请帮帮我...

在此先感谢... :)

Still not refreshing the state dropdown from the second postback..
Please help me if anyone has Idea about this...

Thanks in advance... :)

推荐答案

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>Learn How Add ASP.NET 3.5 AJAX UpdatePanel Triggers</title></head>
<body>
    <form id="form1" runat="server">
<div>



    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <br />
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <asp:Label ID="Label1" runat="server" Text="Country"></asp:Label>
            &nbsp;&nbsp;&nbsp;&nbsp;
            <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"

                onselectedindexchanged="DropDownList1_SelectedIndexChanged">
            </asp:DropDownList>
            <br />
            <asp:Label ID="Label2" runat="server" Text="State"></asp:Label>
            &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="True"

                Enabled="False" onselectedindexchanged="DropDownList2_SelectedIndexChanged">
            </asp:DropDownList>
            <br />
            <asp:Label ID="Label3" runat="server" Text="City"></asp:Label>
            &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <asp:DropDownList ID="DropDownList3" runat="server" AutoPostBack="True"

                Enabled="False" onselectedindexchanged="DropDownList3_SelectedIndexChanged">
            </asp:DropDownList>

            <br />
            <asp:Label ID="Label4" runat="server"></asp:Label>
            <br />
            <br />
        </ContentTemplate>

    </asp:UpdatePanel>



</div>


    </form>


    </body>
</html>

背后的代码：

CODE BEHIND:

public partial class _Default : System.Web.UI.Page 
{
protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        List<string> l1 = new List<string>();
        l1.Add("    ");
        l1.Add("India");
        l1.Add("USA");


        foreach (string item in l1)
        {
            DropDownList1.Items.Add(item);
        }
    }
}


protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList2.Enabled = true;
    DropDownList3.Enabled = false;
    Label4.Text = "";
    List<string> l2 = new List<string>();
 
    if (DropDownList1.SelectedItem.Text == "India")
    {
            DropDownList2.Items.Clear();
             l2.Add(" ");
             l2.Add("Maharashtra");
             l2.Add("Goa");
           
       
        foreach (string item in l2)
        {
            DropDownList2.Items.Add(item);
        }
    }

    else
    {
        DropDownList2.Items.Clear();
            l2.Add(" ");
            l2.Add("Indiana");
            l2.Add("Texas");
        

        foreach (string item in l2)
        {
            DropDownList2.Items.Add(item);
        }
    }


}


protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList3.Enabled = true;
    List<string> l3 = new List<string>();
   
    if (DropDownList2.SelectedItem.Text == "Maharashtra")
    {
        DropDownList3.Items.Clear();
        l3.Add(" ");
        l3.Add("Pune");
        l3.Add("Mumbai");


        foreach (string item in l3)
        {
            DropDownList3.Items.Add(item);
        }
    }

    else if (DropDownList2.SelectedItem.Text == "Goa")
    {

        DropDownList3.Items.Clear();
            l3.Add(" ");
            l3.Add("Panji");
            l3.Add("Vasco");
    

        foreach (string item   in l3)
        {
            DropDownList3.Items.Add(item);
        }
    }

    else if (DropDownList2.SelectedItem.Text == "Indiana")
    {

        DropDownList3.Items.Clear();
        l3.Add(" ");
        l3.Add("Wilkinson");
        l3.Add("Morocco");


        foreach (string item in l3)
        {
            DropDownList3.Items.Add(item);
        }
    }
    else if (DropDownList2.SelectedItem.Text == "Texas")
    {

        DropDownList3.Items.Clear();
        l3.Add(" ");
        l3.Add("Archer City");
        l3.Add("Bryan");


        foreach (string item in l3)
        {
            DropDownList3.Items.Add(item);
        }
    }

}
protected void DropDownList3_SelectedIndexChanged(object sender, EventArgs e)
{
    Label4.Text = DropDownList1.SelectedItem.Text.ToString() + " " + DropDownList2.SelectedItem.Text.ToString() + " " + DropDownList3.SelectedItem.Text.ToString();
}
}

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