Data flow in SwiftUI - from @State to @Observable...
summary
Explains migrating SwiftUI state from @State/@StateObject and Combine to the iOS 17 @Observable macro, showing exactly what code the macro synthesizes (underscore storage, an observation registrar, and access/mutation hooks) and which parts actually notify views. Demonstrates that withObservationTrackingOnChange reports one step behind, that observable objects must be classes (models can’t be structs), and that two-way UI binding uses the new bindable mechanism to connect a Slider to a model’s Double. Claims Combine still works but observable is Apple’s future.
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chapters (21)
- 0:00Introduction
- 1:31From @State to @Observable
- 3:38State and value types
- 5:27Moving controller code out
- 7:14Why views don’t update
- 9:04Combine’s role and limits
- 10:09Introducing @Observable
- 11:14Macro expansion details
- 14:08Computed properties and dependencies
- 15:33Separating model from controller
- 17:00Making model observable
- 17:44Non-observable controller
- 18:47withObservationTracking explained
- 21:14How SwiftUI tracks changes
- 22:40Passing controller to view
- 24:26Binding to observable model
- 25:08Slider binding demo
- 27:17Summary and future
- 28:23Q&A: Migration concerns
- 31:38Q&A: Reference vs value types
- 34:10Q&A: @State vs @StateObject
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