如何添加下拉列表中的默认值 [英] How to add dropdown list default value

问题描述

我使用asp.net从SQL表中读取数据到下拉列表。问题是，当我默认选择的下拉列表。它并不需要的默认值。
请参阅code

 保护无效的Page_Load（对象发件人，EventArgs的发送）
{
    如果（！的IsPostBack）
    {
        conn.Open（）;
        CMD的SqlCommand =新的SqlCommand（选择States_agri *，康恩）;
        SqlDataReader的博士= cmd.ExecuteReader（）;
        ddl_state.DataSource =博士;
        ddl_state.Items.Clear（）;
        ddl_state.Items.Add（ - 请选择state--）;
        ddl_state.DataTextField =Statename的;
        ddl_state.DataValueField =STATEID;
        ddl_state.DataBind（）;
        conn.Close（）;
    }
}
`
 

另请参阅下拉列表ASPX code，供大家参考。

 ＆LT; ASP：的UpdatePanel ID =FormUpdate=服务器的UpdateMode =条件＆GT;
    ＆LT;＆触发器GT;
        ＆LT; ASP：AsyncPostBackTrigger控件ID =ddl_state事件名称=的SelectedIndexChanged/＆GT;
    ＆LT; /触发器＆GT;
    ＆LT;＆的ContentTemplate GT;
        ＆LT;表＆gt;
            ＆所述; TR＆GT;
                 ＆LT; TD＆GT;国家* LT; / TD＆GT;
                 ＆所述; TD＆GT;
                     ＆LT; ASP：DropDownList的ID =ddl_state=服务器的CssClass =cbfld-popup1的AutoPostBack =真OnSelectedIndexChanged =ddl_state_SelectedIndexChanged＆GT;
                     ＆LT; ASP：列表项启用=真实所选=真文本=请选择国家＆GT;＆LT; / ASP：ListItem的＆GT;
                     ＆LT; / ASP：DropDownList的＆GT;
                 ＆LT; / TD＆GT;            ＆LT; / TR＆GT;
            ＆所述; TR＆GT;
                 ＆LT; TD＆GT;区* LT; / TD＆GT;
                 ＆所述; TD＆GT;
                     ＆LT; ASP：DropDownList的ID =ddl_district的CssClass =cbfld-popup1=服务器＆GT;
                     ＆LT; ASP：列表项启用=真实所选=真文本=请选择城市＆GT;＆LT; / ASP：ListItem的＆GT;
                                                                                                      ＆LT; / TD＆GT;
            ＆LT; / TR＆GT;
         ＆LT; /表＆gt;
     ＆LT; /＆的ContentTemplate GT;
＆LT; / ASP：的UpdatePanel＆GT;
 

解决方案

数据绑定后，做到这一点：

  ddl_state.Items.Insert（0，新的ListItem（选择，NA）
 

或标记添加为：

 ＆LT; ASP：DropDownList的.. AppendDataBoundItems =真正的＆GT;
   ＆LT;项目＆GT;
       ＆LT; ASP：ListItem的文本=选择VALUE =/＆GT;
   ＆LT; /项目＆GT;
＆LT; / ASP：DropDownList的＆GT;
 

I am using asp.net for fetching data from sql table to dropdown list. The problem is that, when I give default selection to the dropdown list. It does not take the default value. Please see the code

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        conn.Open();
        SqlCommand cmd = new SqlCommand("select * from States_agri", conn);
        SqlDataReader dr = cmd.ExecuteReader();
        ddl_state.DataSource = dr;
        ddl_state.Items.Clear();
        ddl_state.Items.Add("--Please Select state--");
        ddl_state.DataTextField = "StateName";
        ddl_state.DataValueField = "StateID";
        ddl_state.DataBind();
        conn.Close();
    }
}
`

Also Please see the dropdown list aspx code for your reference.

<asp:UpdatePanel ID="FormUpdate" runat="server" UpdateMode="Conditional">
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="ddl_state" EventName="SelectedIndexChanged" />
    </Triggers>
    <ContentTemplate>
        <table>
            <tr>
                 <td>State*</td>
                 <td>
                     <asp:DropDownList ID="ddl_state" runat="server" CssClass="cbfld-popup1" AutoPostBack="true" OnSelectedIndexChanged="ddl_state_SelectedIndexChanged">
                     <asp:ListItem Enabled="true" Selected="True" Text="Please select State"></asp:ListItem>
                     </asp:DropDownList>
                 </td>

            </tr>
            <tr>
                 <td>District*</td>
                 <td>
                     <asp:DropDownList ID="ddl_district" CssClass="cbfld-popup1" runat="server">
                     <asp:ListItem Enabled="true" Selected="True" Text="Please select city"></asp:ListItem>
                                                                                                      </td>
            </tr>
         </table>
     </ContentTemplate>
</asp:UpdatePanel>

解决方案

After data-binding, do this:

ddl_state.Items.Insert(0, new ListItem("Select","NA")

Or add it in markup as:

<asp:DropDownList .. AppendDataBoundItems="true">
   <Items>
       <asp:ListItem Text="Select" Value="" />
   </Items>
</asp:DropDownList>

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