c# - 如何在组合框中设置默认空值

Question

dr = new MySqlDataAdapter("select tvl_code, 
   concat_ws(',', tvl_code, citi_name) citiname 
   from code_desc where travel_mode = 'BUS'", conn);
ds1 = new DataSet();
dr.Fill(ds1);
ddlfrom.DataSource = ds1;
ddlfrom.DataTextField = "citiname";
ddlfrom.DataValueField = "tvl_code";
ddlfrom.DataBind();

通过这段代码，我将我的组合框绑定(bind)到数据库，并且我能够从我的数据库中填充组合框。但是当我打开页面时，组合框默认包含一个来自数据库的值..意味着名字来 self 填充的数据库列表显示在组合框上。我想在组合框上显示空白。这意味着它不应该显示任何打印，直到我从下拉列表中选择一些东西。如何做到这一点..？？

Answer 1

试试这个:

ddlfrom.Items.Insert(0, "Select...");

像这样:

dr = new MySqlDataAdapter("select tvl_code, concat_ws(',', tvl_code, citi_name) citiname from code_desc where travel_mode = 'BUS'", conn);
ds1 = new DataSet();
dr.Fill(ds1);
ddlfrom.DataSource = ds1;
ddlfrom.DataTextField = "citiname";
ddlfrom.DataValueField = "tvl_code";
ddlfrom.DataBind();
ddlfrom.Items.Insert(0, "Select...");