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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:
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="DropDownList1" runat="server">
</asp:DropDownList>
</div>
</form>
</body>
数据源与绑定:
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。
<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,
<asp:DropDownList ID="DropDownList1" runat="server" >
</asp:DropDownList>
修改Data_Binding()方法,如下:
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:
<asp:DropDownList ID="DropDownList1" runat="server" AppendDataBoundItems="true" OnDataBound="DropDownList1_DataBound" >
</asp:DropDownList>
cs code:
protected void DropDownList1_DataBound(object sender, EventArgs e)
{
DropDownList ddl = (DropDownList)sender;
ddl.Items.Insert(0, new ListItem("--选择--", "0"));
}
为下拉式菜单(DropDownList)添加第一个选项