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>
<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;
}
{
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>
<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>
</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--",""));
}
{
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>
</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"));
}
{
DropDownList ddl = (DropDownList)sender;
ddl.Items.Insert(0, new ListItem("--选择--", "0"));
}