SwiftUI SwiftUI State and Data Flow 3

Question 1

Which framework is the reactive foundation underlying SwiftUI's data flow?

Accepted Answer

Combine

Answer

SwiftUI's property wrappers like `@Published` and `@ObservedObject` are built on Apple's Combine framework.

Question 2

What does the `.onChange(of:perform:)` modifier do?

Accepted Answer

Triggers a closure whenever a specified value changes

Answer

`.onChange(of:perform:)` observes a value and calls the closure with the new value each time it changes.

Question 3

How does SwiftUI determine when to re-render a view?

Accepted Answer

It re-renders when its input state or bindings change

Answer

SwiftUI's diffing engine re-evaluates and re-renders a view only when its declared dependencies (state, bindings, environment) change.

Question 4

What is `@SceneStorage` used for in SwiftUI?

Accepted Answer

Persisting lightweight UI state per scene instance

Answer

`@SceneStorage` persists small amounts of UI state tied to a specific scene, restoring it when the scene is recreated.

Question 5

What is a side effect of marking a class property `@Published` when its setter is called on a background thread?

Accepted Answer

It may cause undefined view update behavior since UI must be updated on the main thread

Answer

SwiftUI view updates must occur on the main thread; publishing on a background thread can cause runtime warnings or undefined behavior.

SwiftUI Practice Test