UIWindow

UIWindow is a subclass of UIView that represents a window in an iOS application using UIKit. It serves as the top-level container for an app’s visible content and participates in the event handling system by acting as the primary receiver of touch and other events within its window scene. Since iOS 13, windows are associated with a window scene (UIScene), allowing multiple windows across scenes within a single app.

A window typically hosts a rootViewController, which manages the content and view hierarchy presented in that window. A window becomes visible when its isHidden property is false and it has been made the key window. The key window receives keyboard input and is the focus for event delivery within its scene. The windowLevel property controls its stacking order relative to other windows.

Key properties include rootViewController, windowScene, screen, isHidden, windowLevel, frame, bounds, alpha, and backgroundColor. Important methods include makeKeyAndVisible(), which makes the window key and displays it on screen. Windows are part of the overall view hierarchy but are not view controllers themselves; instead, they host views via their rootViewController.

In practice, developers create a UIWindow, associate it with a windowScene, assign a rootViewController, and call makeKeyAndVisible to present it. In storyboard-based apps, the system often handles window creation, while in code-based or scene-based setups, manual creation is common. Developers should ensure a window is linked to a scene and avoid creating multiple key windows for the same scene.

Overall, UIWindow provides the top-level context for rendering and event dispatch in an iOS application, forming the bridge between the app’s scene management and its visible content.