22.4 State Objects

Introduced in iOS 14, the State Object property wrapper (@StateObject) is an alternative to the @ObservedObject wrapper. The key difference between a state object and an observed object is that an observed object reference is not owned by the view in which it is declared and, as such, is at risk of being destroyed or recreated by the SwiftUI system while still in use (for example as the result of the view being re-rendered).

Using @StateObject instead of @ObservedObject ensures that the reference is owned by the view in which it is declared and, therefore, will not be destroyed by SwiftUI while it is still needed, either by the local view in which it is declared, or any child views.

As a general rule, unless there is a specific need to use @ObservedObject, the recommendation is to use a State Object to subscribe to observable objects. In terms of syntax, the two are entirely interchangeable:

import SwiftUI

 

struct ContentView: View {

 ...