在asp.net中将默认值添加到下拉列表中

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

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        // 添加默认值
        ddlOptions.Items.Add(new ListItem("默认值", "0"));

        // 添加其他选项
        ddlOptions.Items.Add(new ListItem("选项1", "1"));
        ddlOptions.Items.Add(new ListItem("选项2", "2"));
        ddlOptions.Items.Add(new ListItem("选项3", "3"));
    }
}

<asp:Button ID="btnSubmit" runat="server" Text="提交" OnClick="btnSubmit_Click" />

protected void btnSubmit_Click(object sender, EventArgs e)
{
    string selectedValue = ddlOptions.SelectedValue;
    // 处理用户选择的值
}