🔸environment object

SwiftUI ⟩ view ⟩ environment ⟩ object

An environment object is a state object, which is

1. initialized in an ancester view by adding a @StateObject property

2. and put in the environment by calling the ancester view's .environmentObject(_:) modifier.

To use an environment object In a subview, declare a corrspoinding @EnvironmentObject property in the subview.

// app
struct MyApp: App {
    
    // ⭐️ 1. declare & initialize a state object
    @StateObject private var data = ModelData() 
    
    var body: some Scene {
        WindowGroup {
            RootView()
                // ⭐️ 2. put an environment object.
                .environmentObject(data)         
        }
    }
}

// Subview: RootView's subview
struct Subview: View {

    // ⭐️ get the environment object.
    @EnvironmentObject var data: ModelData      
    
    var body: some View { ... }
}

Be sure to set a corresponding model instance on an ancester view by calling its .environmentObject(_:) modifier.

👥 相關

• ObservableObject：declare an observable object type.
• @Published：declare published values in an observable object type.
• @StateObject：initialize an observable object.
• Use .environmentObject(_:) to put the model object in the environment.
• Use @EnvironmentObject to declare an observable object property provided by an ancestor view.
• observer： any view or object that uses the observable object's data.
• data model：data shared with any views in your app.

📘 手冊

• SwiftUI ⟩ Model data ⟩

  • EnvironmentObject
  • .environmentObject(_:)
• Combine ⟩ ObservableObject (protocol)
• SwiftUI ⟩ Model data ⟩ @ObservedObject (property wrapper)

📗 參考

• Majid ⟩ The difference between @StateObject, @EnvironmentObject, and @ObservedObject in SwiftUI #todo