SwiftUI - Performance and Memory Management
- 1. Andrei Solovev, iOS Tech Lead at Seven Peaks Software SwiftUI Performance and Memory Management
- 2. SwiftUI SwiftUI automatically updates the a ff ected parts of the interface. As a result, the framework automatically performs most of the work traditionally done by view controllers.
- 3. Topic • ObjectWillChange and @Publishe d • NavigationLink performanc e • Creating @ObservedObject with parameters
- 4. ObjectWillChange • ObservableObjec t • @StateObject and objectWillChang e • @StateObject and @Publishe d • @ObservedObject and @Publishe d • Unused @ObservedObject
- 5. ObservableObject A type of object with a publisher that emits before the object has changed. By default an ObservableObject synthesizes an objectWillChange publisher that emits the changed value before any of its @Published properties changes . class Contact: ObservableObject { @Published var name: String } https://developer.apple.com/documentation/Combine/ObservableObject
- 6. @StateObject and objectWillChange objectWillChange A publisher that emits before the object has changed. var objectWillChange: Self.ObjectWillChangePublisher { get } https://developer.apple.com/documentation/combine/observableobject/ objectwillchange-2oa5v
- 7. @StateObject and @Published Avoid the overhead of a published property when you don’t need it. Only publish properties that both can change and that matter to the user interface.
- 8. @ObservedObject and @Published SwiftUI might create or recreate a view at any time, so it’s important that initializing a view with a given set of inputs always results in the same view. As a result, it’s unsafe to create an observed object inside a view.
- 9. Unused @ObservedObject SwiftUI monitors observable object changes, not a particular property and View will be updated even if you don’t use the property that changed
- 10. NavigationLink A view that controls a navigation presentation. A NavigationLink de fi nes a destination for a navigation-based interface and allows the user to perform that navigation. Optionally, you can use the NavigationLink to perform a navigation programmatically • LazyVie w • Deep Navigatio n
- 11. LazyView To solve the problem when a parent View creates all children Views that could be used for navigation we can introduce LazyView, that would take factory closure that creates a new View and execute it on rendering, means only when this view is going to be presented on the screen.
- 12. Deep Navigation Sometimes there are multi-step flow when you have to present multiple Views with next button and then do some action on the last screen, most common case it’s a Sign Up where used could enter Email on first screen, Password on seconds, then OTP and Success in the end.
- 13. Creating @ObservedObject with parameters • @StateObjec t • @ObservedObjec t • Caching @ObservedObjec t
- 14. @StateObject A property wrapper type that instantiates an observable object. Create a state object in a View, App, or Scene by applying the @StateObject attribute to a property declaration and providing an initial value that conforms to the ObservableObject protocol : https://developer.apple.com/documentation/swiftui/stateobject
- 15. @ObservedObject A property wrapper type that subscribes to an @observable object and invalidates a view whenever the observable object changes . https://developer.apple.com/documentation/swiftui/observedobject
- 16. Caching @ObservedObject Everytime @ObservableObject emits changes every View that owns this object as @EnvironmentObject, @StateObject or @ObservedObject will be recreated and the body will be executed automatically by SwiftUI, even if this view doesn’t use the property that was changed. It could be done multiple times per user action or some event triggered. That means we have to keep View’s init() and body as simple as possible and keep free from any kind of calculations and object creations.