asp.net-mvc 将空值添加到 ASP.net MVC 中的 DropDownList
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Add empty value to a DropDownList in ASP.net MVC
提问by jvanderh
I'm building a data entry interface and have successfully bound the columns that have reference tables for their data using DropDownList so the user selects from the pre-configured values.
我正在构建一个数据输入界面，并使用 DropDownList 成功绑定了具有数据引用表的列，以便用户从预配置的值中进行选择。
My problem now is that I don't want the first value to be selected by default, I need to force the user to select a value from the list to avoid errors where they didn't pick that field and by default a value was assigned.
我现在的问题是我不希望默认情况下选择第一个值，我需要强制用户从列表中选择一个值以避免错误，因为他们没有选择该字段并且默认情况下分配了一个值.
Is there a more elegant way of doing this than to add code to include an empty value at the top of the list after I get it from the database and before i pass it to the SelectList constructor in my controller class?
有没有比在我从数据库中获取空值之后以及将它传递给控制器类中的 SelectList 构造函数之前添加代码以在列表顶部包含一个空值更优雅的方法？
回答by Ropstah
The Html helper function takes a 'first empty value' parameter as the third argument.
Html 辅助函数将“第一个空值”参数作为第三个参数。
<%=Html.DropDownList("name",dataSource,"-please select item-")%>
回答by qulzam
You can also use this way:
您也可以使用这种方式：
dropdownlist.DataTextField = ds.Tables[0].Columns[0].Caption;
dropdownlist.DataValueField = ds.Tables[0].Columns[1].Caption;
dropdownlist.DataSource = ds;
dropdownlist.DataBind();
dropdownlist.Items.Insert(0, new ListItem("Select ...", string.Empty));
