ASP.NET DropDownList / HTML select list default selection

Question

For my ASP.NET page, in the code behind I load various items/options into a DropDownList but I do not set a default by assigning SelectedIndex. I notice for the postback SelectedIndex is set to 0, even if I never set focus to or changed the value in the DropDownList.

If not otherwise specified in the code behind or markup, will a default value of 0 be used for the SelectedIndex in a postback with a DropDownList? If yes, is this part of the HTML standard for selection lists, or is this just the way it is implemented for ASP.NET?

Answer 1

This is normal behavior for the HTML SELECT control.

Unless the selected property is used, it will always start at the first item (index of 0).

In many cases, I don't want this in ASP.NET because I specifically want the user to select an option.

So what I do is add a blank item which I can then validate.

i.e.

<asp:DropDownList runat="server" DataSourceID="SomeDS" AppendDataBoundItems="true"> // Notice the last property
    <asp:ListItem Text="Please select an option" Value="" />
</asp:DropDownList>

This way, I can set a validator which checks if the value is blank, forcing the user to make a selection.