DropDownList ,select 添加默认 选项的几种方法

 

1.       <asp:DropDownList ID="DropDownList1" runat="server">
            </asp:DropDownList>
            <asp:DropDownList ID="DropDownList2" runat="server" AppendDataBoundItems="true">
                <asp:ListItem Text="请选择" Value=""></asp:ListItem>
            </asp:DropDownList>
2.    /**//*
    protected void DropDownList1_DataBound(object sender, EventArgs e)
    {
        DropDownList1.Items.Insert(0, new ListItem("--请选择--", ""));
    }*/
3.

protected void Page_Load(object sender, EventArgs e)
    ...{
        if (!IsPostBack)
        ...{
            //DropDownList的属性AppendDataBoundItems
            //功能：指示是否在数据绑定之前清除列表           
            DropDownList1.AppendDataBoundItems = true;

            DropDownList1.Items.Add(new ListItem("-- 请选择一个选择项 --", ""));

          DropDownList1.DataSource = CreateDataSource();         }
    }
4.

protected void Page_Load(object sender, EventArgs e)
    ...{
        if (!IsPostBack)
        ...{
              DropDownList1.DataSource = CreateDataSource();
             DropDownList1.Items.Insert(0,new ListItem("-- 请选择一个选择项 --", ""));
        }
    }