In what process does the updating of the displayed user interface occur?

The process of updating the displayed user interface is called rendering. In iOS, this usually involves a UI update cycle that includes the following steps:

1. Changing the model data or state.
2. Calling methods that update the views (e.g., setNeedsDisplay or setNeedsLayout).
3. The system schedules a redraw and calls drawing methods (drawRect, etc.) on the next run loop cycle.

Thus, when data changes, a UI update is triggered, and the system redraws the screen to display the current state.