C# 将空白选择项添加到下拉列表中的列表中
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Adding a blank selection item to the list in drop down list
提问by sarsnake
my dropdownlist is populated from the database as in:
我的下拉列表是从数据库中填充的，如下所示：
DataTable dt = GetData(); ddlMylist.DataSource = dt; ddlMylist.DataBind();
数据表 dt = GetData(); ddlMylist.DataSource = dt; ddlMylist.DataBind();
Now dt contains the data, and I wish to add "Select" word to the top of the list when the selection is blank. It seems as there is no option other than add it to the dt (DataTable object)....but it seems wrong somehow.
现在DT包含数据，并且在选择空白时，我希望将“选择”单词添加到列表顶部。似乎除了将其添加到 dt（DataTable 对象）之外别无选择……但不知何故似乎是错误的。
What are other options. It's doesn't have to be the word "Select" it can be just an empty space...Currently, upon page load I can see the first data item in the list which is all good and dandy, but I have 3 drop downs that are co-dependent, and I want the user to explicitly make a selection which will trigger other drop downs to populate accordingly.
还有什么其他选择。它不一定是“选择”这个词，它可以只是一个空白空间......目前，在页面加载时，我可以看到列表中的第一个数据项，这一切都很好，但我有 3 个下拉列表是相互依赖的，我希望用户明确做出一个选择，这将触发其他下拉菜单相应地填充。
采纳答案by Phil Sandler
Try:
尝试：
ddlMylist.Items.Insert(0, new ListItem([key], [text]));
ddlMylist.SelectedIndex = 0;
You do this after you databind to your source.
在数据绑定到源之后执行此操作。
回答by Cory Charlton
Try:
尝试：
DDL.Text = string.Empty;
Edit:
编辑：
I know this works when I'm manually adding items but I'm not sure if it will when a DataSource is bound.
我知道这在我手动添加项目时有效，但我不确定在绑定 DataSource 时是否有效。
回答by Joel Coehoorn
Your dropdownlist markup should look like this:
您的下拉列表标记应如下所示：
<asp:DropDownList ID="ddlMylist" runat="server" AppendDataBoundItems="true">
<asp:ListItem Text="-Select-" Value="" />
</asp:DropDownList>
Note the AppendDataBoundItemsattribute.
注意AppendDataBoundItems属性。
回答by COMPILER
Try this one:
试试这个：
ddlMylist.Items.Insert(0, "Select");
