What's the need for UIPresentationController beside helping with trait collection in iOS?

Question

What are the benefits of UIPresentationController over Just using adding subviews and animating the view you want to present in? It appears to be a little be cumbersome with all the protocol it must conform to and many people still prefer presenting their view with simple frame animation. What was Apple logic in introducing the class?

Answer 1

Presentation machinery was a part of UIKit long before UIPresentationController was introduced. UIPresentationController gives more flexibility and allows for creating custom presentations apart from built-in ones (fullscreen, current context, popover, etc). There is a number of reasons for the presentation machinery and UIPresentationController to exist:

• Managing view hierarchies. Whenever you want to present the view you don't always own the presenting view controller. Usually it's discouraged to interfere with the sub-hierarchy of the view controller you don't own but in the case of the presentation you would need to add the presented view controller's view as a child of the presenting view controller's view (or its superview). It becomes more complicated when in-context presentation chains are involved (for example popover -> current context -> share sheet). When presentation machinery is used UIKit takes care of view hierarchy management in a consistent way. It also establishes a container view for the UIPresentationController class to let it focus on managing only the views participating in the presentation. UIPresentationController class may choose to add arbitrary decoration and shadow views to the container view and respond to layout changes in containerViewWillLayoutSubviews method.
• Managing modality. View controllers are presented and dismissed in a very particular order and presentation controller APIs enforce this. Presentation machinery also makes sure that interaction is disabled for the views that became obscured by the presentation.
• Maintaining view controller hierarchy. Presentation controllers could be viewed as a more specific type of view controller containment, they make sure presented view controllers are still a part of a view controller hierarchy. This is necessary for trait collection propagation, appearance callbacks, sending viewWillTransitionToSize:withTransitionCoordinator:, performing view controller transitions (including nested presentations) and a lot more.
• Managing first responders. When the presentation happens the current first responder is stashed away and then restored after the dismissal.