c# - 为从数据库中填充的下拉列表设置默认值

Question

我正在从数据库中填充我的下拉列表，但我想将“请选择一个项目”与其他选项一起添加到下拉列表中，并使其成为默认选定项目:
我尝试设置writerddl.SelectedValue = "please...";但运行时错误显示:

'writerddl' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value

这是我的代码:

protected void Page_Load(object sender, EventArgs e)
{
writerddl.SelectedValue = "please...";
if (!IsPostBack)
  {
   writerddl.DataSource = DS.show_all_writers();
   writerddl.DataValueField = "writerid";
   writerddl.DataTextField = "writersname";            
   writerddl.DataBind();
  }
}

Answer 1

试试这段代码。

protected void Page_Load(object sender, EventArgs e)
{       
   if (!IsPostBack)
   {
       writerddl.DataSource = DS.show_all_writers();
       writerddl.DataValueField = "writerid";
       writerddl.DataTextField = "writersname";            
       writerddl.DataBind();
       writerddl.Items.insert(0, new ListItem("Please select",""));
   }
}