How swiftui re render?

SwiftUI re-renders views based on changes in state. When the state of a view changes, SwiftUI automatically updates the UI to reflect these changes. This is because SwiftUI views are state-driven and declarative. They are not long-lived object instances that receive imperative commands over time. Instead, they are value types defined using structs, which describe what the current state of the UI should be.

When a view's state changes, SwiftUI creates new view values and uses them to determine how to update its outputs. This process eliminates boilerplate code and reduces update bugs. SwiftUI maintains a representation of the user interface behind the scenes, and as data changes, it updates the UI accordingly.

For example, if you have a view that displays a list of pets and their tricks, and you modify a pet object to indicate it has received an award, SwiftUI will track any views that depend on this pet. It will call the view's body again with the updated pet, and the UI will be updated to display the new information, such as an image reflecting the award.

Additionally, SwiftUI provides tools for state management, such as @State and @Binding, which help manage the internal state of views and create dependencies between views and their data sources.

For more details, you can refer to the session SwiftUI essentials (08:50).