SwiftUI ObservedObject Wrapper

Main Idea

When using observed objects there are three key things we need to work with: the ObservableObject protocol is used with some sort of class that can store data, the @ObservedObject property wrapper is used inside a view to store an observable object instance, and the @Published property wrapper is added to any properties inside an observed object that should cause views to update when they change.

Tip: It is really important that you use @ObservedObject only with views that were passed in from elsewhere. You should not use this property wrapper to create the initial instance of an observable object – that’s what @StateObject is for.

Link

• SwiftUI ObservableObject Wrapper
• SwiftUI StateObject Wrapper

Usage

class UserProgress: ObservableObject {
    @Published var score = 0
}

struct InnerView: View {
    @ObservedObject var progress: UserProgress

    var body: some View {
        Button("Increase Score") {
            progress.score += 1
        }
    }
}

struct ContentView: View {
    @StateObject var progress = UserProgress()

    var body: some View {
        VStack {
            Text("Your score is \(progress.score)")
            InnerView(progress: progress)
        }
    }
}