CODEWITHSUNDEEP
swiftswiftui
john doe
john doe

Reputation: 9660

Change Notification from Observable Object as a Nested Object in SwiftUI

I have a following scenario.

I have AppState which consists of an object of type Foo. Foo has a counter variable and I want to call objectWillChange when counter value updates so I can update the UI.

At present nothing happens. The increment function gets called but the UI never gets updated.




import Foundation
import Combine

class Foo: ObservableObject {
    @Published var counter: Int = 999
    
    func increment() {
        counter += 1 // how to get notified when counter value changes
    }
}

class AppState: ObservableObject {
    
    @Published var foo: Foo = Foo()
}

// usage in Scene Delegate as Environment Object
let appState = AppState()

// Use a UIHostingController as window root view controller.
if let windowScene = scene as? UIWindowScene {
    let window = UIWindow(windowScene: windowScene)
    window.rootViewController = UIHostingController(rootView: accountSummaryScreen.environmentObject(appState))

UPDATE

class Foo: ObservableObject {
    @Published var counter: Int = 999 {
        didSet {
            objectWillChange.send() 
        }
    }
    
    func increment() {
        counter += 1 // how to get notified when counter value changes
    }
}

Upvotes: 3

Views: 1645

Answers (2)

malhal
malhal

Reputation: 30582

In SwiftUI our model types are structs, e.g.

struct Foo: Identifiable {
    let id = UUID()
    var counter: Int = 999 
    
    mutating func increment() {
        counter += 1 
    }
}

Now it can be used with @Published in an ObservableObject.

Upvotes: 1

New Dev
New Dev

Reputation: 49590

Changes aren't detected because Foo, being a reference-type, doesn't actually change - it's the same reference, so @Published doesn't help here.

AppState would need to manually subscribe to changes and call its own objectWillChange.send:

class AppState: ObservableObject {
    
    var foo: Foo = Foo() {
       didSet {
          cancellables = []
          foo.$counter
             .map { _ in } // ignore actual values
             .sink(receiveValue: self.objectWillChange.send)
             .store(in: &cancellables)
       }
    }

    private var cancellables: Set<AnyCancellable> = []
}

Upvotes: 3

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