UIContentContainer

UIContentContainer is a protocol in UIKit that defines the interface for objects that act as containers for other view controllers. Container view controllers adopt this protocol to coordinate the presentation and layout of their content with the system and with their child view controllers. The protocol establishes a lightweight contract that enables consistent handling of content size and related updates across different container implementations.

A central responsibility of UIContentContainer is to provide and respond to content size information. The protocol introduces a mechanism for a container to communicate its preferred content size and to react when a child's preferred size changes. This supports dynamic layouts such as popovers, split views, and other container-driven presentations. A typical container uses the preferred content size to inform layout decisions and adjust its own bounds or child layout accordingly. When a child reports a different preferred size, the container can update its layout by implementing the relevant notification method.

In practice, UIContentContainer is used in conjunction with the view controller containment APIs in UIKit. Container controllers that host child view controllers rely on this protocol to manage how content is sized and displayed. Examples of container controllers that implement the container pattern include split view controllers and other custom container controllers that arrange, size, or transition their children.

Overall, UIContentContainer provides a standardized, minimal interface that helps the system coordinate content sizing and presentation within a hierarchy of view controllers. See also: UIViewController containment, preferredContentSize, and related presentation APIs.