ASP.net DropDownList with no selected item

问题

I have a ASP DropDownList with items added to it. All what I want is to make the selection after the page loaded empty so there is no a selected item.

How can I do that?

回答1:

You can add an empty item to the top of your dropdownlist programmatically like this:

myDropDown.Items.Insert(0, new ListItem(string.Empty, string.Empty));
myDropDown.SelectedIndex = 0;

回答2:

Not sure I understand your question but try this:

DropDownList1.ClearSelection()

or

DropDownList1.SelectedIndex = -1;

回答3:

You can set the SelectedIndex property to -1 or you can add an empty entry as the first item in the data source and validate the selection on form submission.

回答4:

This should work on the client side:

<asp:DropDownList ID="YourID" runat="server" DataSourceID="YourDataSource
DataTextField="Text" DataValueField="Value" AppendDataBoundItems="True">
    <asp:ListItem Text="" Selected="True"></asp:ListItem>
</asp:DropDownList>

回答5:

yourDropDownList.Items.Clear()

To repopulate, you can either add items statically as per womps suggestion (substituting params in the insert() method, or you can populate it dynamically from a data source. The backing store for list items is the ListItemCollection.

回答6:

If the dropdownlist is being populated by DataSource, is important do the DataBind before the insert. Otherwise the item insertion does not happen.

myDropDown.DataBind();
myDropDown.Items.Insert(0, new ListItem(string.Empty, string.Empty));
myDropDown.SelectedIndex = 0;

https://stackoverflow.com/a/2224636/1467453

来源：https://stackoverflow.com/questions/2224611/asp-net-dropdownlist-with-no-selected-item