In what way inside the text field? If you put it inside the area where the use can write, the button would go over the text, or what is the idea?
If you want to have it inside the TextField border, disable the default border, and make a composite component with CustomComponent that has the borderless TextField and the small button, and then enable border for the CustomComponent. Use a PopupView, Select/ComboBox, or something for the popup menu; see the
SplitButton example .
Why isn’t using just plain ComboBox suitable in your case?