The UI elements provided by UIKit fall into four broad categories:
Bars. Bars contain contextual information that tells users where they are and controls that help users navigate or initiate actions.
Content views. Content views contain app-specific content and can enable behaviors such as scrolling, insertion, deletion, and rearrangement of items.
Controls. Controls perform actions or display information.
Temporary views. Temporary views appear briefly to give users important information or additional choices and functionality.