The link you showed is talking about a database from what I can see?
But in the case of that not being the target you can set a combobox for style csSimple which will show only an edit box but no
drop down.
At Runtime, you adjust the height of the Combobox to what you need to accommodate your requirements for a drop list.
You do this in the OnClick event where you can test the current height of the box to know if you wish to shorten it or open it.
Ensure any controls sitting on the form where this box will be painted have a lower Z order so they get covered up.