What is the difference between `@State`, `@Binding`, `@ObservedObject`, and `@StateObject`?

Answer: These are SwiftUI's property wrappers for state management — each has a distinct ownership and lifecycle role.

Wrapper	Owns data?	Source
@State	✅ Yes	Local to the view
@Binding	❌ No	Passed in from parent
@StateObject	✅ Yes	Owns the ObservableObject
@ObservedObject	❌ No	Injected from outside
@EnvironmentObject	❌ No	Injected via environment

Code Example:

// Parent creates and owns the object
struct ParentView: View {
    @StateObject private var viewModel = CounterViewModel()

    var body: some View {
        ChildView(count: $viewModel.count) // passes binding
    }
}

// Child receives a binding — does not own the data
struct ChildView: View {
    @Binding var count: Int

    var body: some View {
        Button("Increment") { count += 1 }
    }
}

Key Rule:

• Use @StateObject when the view creates the object
• Use @ObservedObject when the object is created elsewhere and passed in