A graphical user interface lets a user inspect and manipulate a program through visual controls such as windows, buttons, menus and text fields. A GUI widget combines a displayed representation with interaction behavior. Input events select a control or action, while application state determines what is drawn next.
For example, pressing a button can initiate a calculation and later display its result. The Event handler should not have to embed every computational detail; separating the underlying model from its view makes other interfaces and tests possible. Qt Widgets provides visual elements, layout management and event handling as separate cooperating mechanisms.[ref]
Qt Widgets documentation. Widgets, Layouts and Model/View Classes
A visible control is therefore an interaction interface, not an authorization boundary or proof that the requested action succeeded.