App structure and lifecycle

SwiftUI applications are defined using the App protocol, which provides a clear and concise way to declare the structure and behavior of the app. It acts as the entry point for execution and defines the scenes that make up the app's user interface. Scenes, in turn, represent distinct parts of the app, each managing its own view hierarchy and lifecycle.

This chapter explores how the App protocol works and how scenes are used to structure an app's interface. We'll discuss the different types of scenes available, including WindowGroup for multi-window support and DocumentGroup for document-based workflows, as well as platform-specific options like Settings for macOS. Additionally, we'll examine how SwiftUI manages the lifecycle of apps and scenes automatically and how we can monitor and respond to lifecycle transitions to handle changes in application state effectively.