Apple's documentation pretty much only says this about 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.".
And this sample seems to behave the same way, with or without conformance to the protocol by Contact:
import UIKit
import Combine
class ViewController: UIViewController {
let john = Contact(name: "John Appleseed", age: 24)
private var cancellables: Set<AnyCancellable> = []
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
john.$age.sink { age in
print("View controller's john's age is now \(age)")
}
.store(in: &cancellables)
print(john.haveBirthday())
}
}
class Contact {
@Published var name: String
@Published var age: Int
init(name: String, age: Int) {
self.name = name
self.age = age
}
func haveBirthday() -> Int {
age += 1
return age
}
}
Can I therefore omit conformance to ObservableObject every time I don't need the objectWillChange publisher?
You only need the ObservableObject conformance if you need a SwiftUI view to be auto-updated when an @Published property of your object changes. You also need to store the object as @ObservedObject or @StateObject to get the auto-updating behaviour and these property wrappers actually require the ObservableObject conformance.
As you're using UIKit and hence don't actually get any automatic view updates, you don't need the ObservableObject conformance.