为下拉式菜单(DropDownList)添加第一个选项

很多方法可以为为下拉式菜单(DropDownList)添加第一个选项，下面是Insus.NET小结了几个方法，仅供参考：

Html code:

View Code

< body >
     < form id ="form1" runat ="server" >
     < div >
         < asp:DropDownList ID ="DropDownList1" runat ="server" >
         </ asp:DropDownList >
     </ div >
     </ form >
</ body >

数据源与绑定：

View Code

protected void Page_Load( object sender, EventArgs e)
    {
         if (!IsPostBack)
        {
            Data_Binding();
        }
    }

     private void Data_Binding()
    {
         this.DropDownList1.DataSource = Site();
         this.DropDownList1.DataTextField = " key ";
         this.DropDownList1.DataValueField = " value ";
         this.DropDownList1.DataBind();
    }

     private Dictionary< string, string> Site()
    {
        Dictionary< string, string> site = new Dictionary< string, string>();
        site.Add( " Insus.NET cnblogs ", " http://insus.cnblogs.com ");
        site.Add( " Microsoft ", " http://www.microsoft.com ");
        site.Add( " Google ", " http://www.google.com ");
         return site;
    }

以下所有方法，均以以上html或code作变动。

第一种，修改Html Code，把DropDownList属性AppendDataBoundItems的值设为true,然后直接添加一个item:<asp:ListItem Text="--选择--" Value=""></asp:ListItem> 在DropDownList内。

View Code

< asp:DropDownList ID ="DropDownList1" runat ="server" AppendDataBoundItems ="true" >
         < asp:ListItem Text ="--选择--" Value ="" ></ asp:ListItem >
         </ asp:DropDownList >

第二种方法，Html Code无需更改，

View Code

< asp:DropDownList ID ="DropDownList1" runat ="server" >
</ asp:DropDownList >

修改Data_Binding()方法，如下：

View Code

private void Data_Binding()
    {
         this.DropDownList1.DataSource = Site();
         this.DropDownList1.DataTextField = " key ";
         this.DropDownList1.DataValueField = " value ";
         this.DropDownList1.DataBind();

         // 添加下面代码：
        DropDownList1.Items.Insert( 0, new ListItem( " --选择-- ", ""));

    }

第三种方法：

Html改为如下，设置AppendDataBoundItems属性与及实现OnDataBound事件：

View Code

< asp:DropDownList ID ="DropDownList1" runat ="server" AppendDataBoundItems ="true" OnDataBound ="DropDownList1_DataBound" >
</ asp:DropDownList >

cs code:

View Code

protected void DropDownList1_DataBound( object sender, EventArgs e)
    {
        DropDownList ddl = (DropDownList)sender;
        ddl.Items.Insert( 0, new ListItem( " --选择-- ", " 0 "));
    }

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为下拉式菜单(DropDownList)添加第一个选项

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