Data Essential in SwiftUI - 2020

#learning Data Essential in SwiftUI - 2020

• @State create a new source of truth
• @Binding create a reference to the source of truth allow write access to that state

Performance consideration: avoid Repeated Heap allocation problem

• @ObservableObject allow multiple SwiftUI view to subscribe to its changes (specifically before the property will change)
• ObservableObject protocol is for class (reference type only), which mean it will be kept alive in the memory if there is reference to it
• Class follow this protocol will usually need to have @Published property that will trigger event that ties to SwiftUI view updates
• ObservableObject can be used to provide a single source of truth through view / app hierarchy
• @Published can be used to mark property can be observed or bound to (Binding)

• ObservableObject can be used to provide a single source of truth through view / app hierarchy, either as a single Instance (one object) or multiple instances

There is 3 way that View can subscribe to changes of @ObservableObjects

• @ObservedObject, the life cycle of the observed object is not managed by view life cycle, but somewhere else
• @StateObject , the object is only initiated just before body of the view is created, and destroyed when the view is no longer rendered. In short, life-cycle of the object is managed by the view
• @EnvironmentObject is usually used when we want to create a globally shared Source of truth

Data Life-cycle

• Tied to the way we defined it

• Scene is new screen or new window instance, think Split view in ipad, windows in macos