Just like UIKit, SwiftUI is implemented on top of an event loop that dispatches messages to your UI code. The UI code in turn may trigger parts of the screen to be re-rendered. The handling of messages and rendering of graphics on screen form the render loop of an application. All UI frameworks are based on a render loop, in SwiftUI it is hidden particularly well. Most of the time, it works under the hood without us needing to know anything about it. It is amazing how we can write UI code without even needing to understand what an event loop is, and without us needing to worry about how often to render screen content. But in some cases, it is useful to know what is happening behind the scenes.