强制asp.net dropdownlist扩展。

I have an ASP.NET data bound dropdownlist which is populated based on the contents of a textbox. After it is populated I would like to expand the dropdownlist automatically, so that the user realizes that a choice needs to be made and doesn't need to click on the dropdown to expand it. There doesn't seem to be a property or method do do this.I have an ASP.NET data bound dropdownlist which