How to perform textbox and dropdownlist in one control?

For example : I have UserID and UserName. So I use DropDownList. UserName is DataTextField and UserID is DataValueField. So User can choose their name and I save UserID to my database. But If User is new and not regi开发者_JAVA技巧stered. I want to allow to type in DropDownList and I save the name to database. So for registered people can choose and not registered people can key in.

How should I do? Can anybody give me suggestions? Thanks

What you want is an editable dropdown:

http://www.google.com.au/search?source=ig&hl=en&rlz=&q=editable%20dropdown&meta=

How can I create an editable dropdownlist in HTML?

http://msdn.microsoft.com/en-us/library/aa511458.aspx

http://demos.telerik.com/aspnet-ajax/combobox/examples/overview/defaultcs.aspx