SwiftUI: How to persist @Published variable using UserDefaults?

import SwiftUI
import Combine

fileprivate var cancellables = [String : AnyCancellable] ()

public extension Published {
    init(wrappedValue defaultValue: Value, key: String) {
        let value = UserDefaults.standard.object(forKey: key) as? Value ?? defaultValue
        self.init(initialValue: value)
        cancellables[key] = projectedValue.sink { val in
            UserDefaults.standard.set(val, forKey: key)
        }
    }
}

class Settings: ObservableObject {
    @Published(key: "isLogedIn") var isLogedIn = false
    ...
}

Sample: https://youtu.be/TXdAg_YvBNE

Version for all Codable types check out here

To persist your data you could use the @AppStorage property wrapper. However, without using @Published your ObservableObject will no longer put out the news about the changed data. To fix this, simply call objectWillChange.send() from the property's willSet observer.

import SwiftUI

class Settings: ObservableObject {
    @AppStorage("Example") var example: Bool = false {
        willSet {
            // Call objectWillChange manually since @AppStorage is not published
            objectWillChange.send()
        }
    }
}

It should be possible to compose a new property wrapper:

Composition was left out of the first revision of this proposal, because one can manually compose property wrapper types. For example, the composition @A @B could be implemented as an AB wrapper:

@propertyWrapper
struct AB<Value> {
  private var storage: A<B<Value>>

  var wrappedValue: Value {
    get { storage.wrappedValue.wrappedValue }
    set { storage.wrappedValue.wrappedValue = newValue }
  }
}

The main benefit of this approach is its predictability: the author of AB decides how to best achieve the composition of A and B, names it appropriately, and provides the right API and documentation of its semantics. On the other hand, having to manually write out each of the compositions is a lot of boilerplate, particularly for a feature whose main selling point is the elimination of boilerplate. It is also unfortunate to have to invent names for each composition---when I try the compose A and B via @A @B, how do I know to go look for the manually-composed property wrapper type AB? Or maybe that should be BA?

Ref: Property WrappersProposal: SE-0258