What is the difference between ObservedObject and StateObject in SwiftUI

n SwiftUI, both @ObservedObject and @StateObject are property wrappers used for managing external state within a view. However, they are used in slightly different scenarios and have different lifecycle management behaviors:

1. @ObservedObject:
   • Used to declare a dependency on an external object that conforms to the ObservableObject protocol.Typically used when a view needs to observe and react to changes in the state of an object that it doesn’t own or control.The observed object is instantiated and managed by the parent view or an external source, and the view updates itself whenever the observed object changes.When the observed object is mutated externally (e.g., by a parent view or a view model), SwiftUI automatically updates the view to reflect the changes.
   Example:

• Purpose: Use @ObservedObject when you have an object that is not tightly coupled to a specific view and should be shared across multiple views.
• Lifecycle Management:
  • The observed object’s lifecycle is managed externally (usually by a parent view).
  • It remains alive even if the current view is destroyed.
  • Multiple views can observe the same object.

struct ContentView: View {
    @ObservedObject var viewModel: MyViewModel
    
    var body: some View {
        Text(viewModel.text)
    }
}

@StateObject:

• Introduced in SwiftUI 2.0 and is used to declare a property that owns and manages its own instance of an ObservableObject.
• Suitable when a view needs to create and manage its own instance of an observable object, ensuring that the object’s lifecycle is tied to the view’s lifecycle.
• SwiftUI creates a new instance of the ObservableObject and associates it with the property only once during the view’s initialization, and then it retains and reuses the same instance for subsequent updates.
• This is particularly useful when you need to ensure that the observable object persists across view updates without being recreated each time.

Example:

• Purpose: Use @StateObject when you have an object that is tightly coupled to a specific view and should be destroyed when the view is destroyed.
• Lifecycle Management:
  • The state object’s lifecycle is tied to the current view that creates it.
  • It is automatically destroyed when the view is removed.
  • Only the view that owns it can observe it.

struct ContentView: View {
    @StateObject var viewModel = MyViewModel()
    
    var body: some View {
        Text(viewModel.text)
    }
}

In summary, @ObservedObject is used to observe changes in external objects, whereas @StateObject is used to manage the lifecycle of objects owned by the view itself. Choosing between them depends on whether you need to manage the object’s lifecycle explicitly or if you’re observing changes in an externally managed object.

Ownership Distinction:

• The key difference lies in ownership:
  • @StateObject: The view that creates the object is its owner.
  • @ObservedObject: Other views observe the object but don’t own it directly.

Remember these distinctions when choosing between @StateObject and @ObservedObject. Happy SwiftUI coding