How is the state tracking mechanism implemented with ObservedObject?

In SwiftUI, the state observation mechanism using @ObservedObject is based on the ObservableObject protocol and publishing changes through @Published.

When a class is marked as ObservableObject, it can notify subscribers about changes to its properties. Properties marked as @Published automatically generate events when their values change. A SwiftUI component that uses @ObservedObject subscribes to these events and redraws when they occur.

Example:

class UserSettings: ObservableObject {
    @Published var username: String = "Guest"
}

struct ContentView: View {
    @ObservedObject var settings = UserSettings()

    var body: some View {
        Text("Hello, \(settings.username)!")
    }
}

Here, when username in UserSettings changes, the ContentView interface automatically updates.