🚥StateObject

SwiftUI ⟩ Data Flow ⟩ StateObject

💾 程式

📗 參考：Swift Playgrounds (Keep Going with Apps) - Sharing Data Between Views.

📁 CreatureZoo

// ⭐️ 1. declare @ObservableObject
class CreatureZoo : ObservableObject {
    // ⭐️ 2. source of truth (@Published properties)
    @Published var creatures = [
        Creature(name: "Gorilla", emoji: "🦍"),
        Creature(name: "Peacock", emoji: "🦚"),
    ]
}

📁 MyApp

@main
struct MyApp: App {
    
    // ⭐️ 3. create data in app
    @StateObject var data = CreatureZoo()
    
    var body: some Scene {
        SPCAssessableWindowGroup(app: self, assessmentCandidates: [CreatureZoo()]) {
            NavigationView { 
                ContentView()
                    .navigationTitle("My Creatures")
            }
            // ⭐️ 4. put data in environment
            .environmentObject(data)
        }
    }
}

📁 ContentView

struct ContentView: View {
    
    // ⭐️ 5. inject data from environment
    @EnvironmentObject var data : CreatureZoo

    var body: some View {
        SPCAssessableGroup(view: self) {
            List {
                Text("ContentView")
                
                Section("Dance") {
                    NavigationLink("Make the Creatures Dance") { 
                        DancingCreatures()
                            .navigationTitle("Dancing Creatures")
                    }
                }
                
                // ⭐️ 6. use data
                ForEach(data.creatures) { creature in 
                    // ...
                }    
            }
        }
    }
}

🔴 主題

• Binding from StateObject

📗 參考

• How to initialize @StateObject with parameters in SwiftUI

• Sarun ⟩ Should we manually call @StateObject initializer

🔸 定義

StateObject 是一個 Property Wrappers，它內含的資料一定要遵循 ObservableObject 協定。

@frozen @propertyWrapper 
struct StateObject<ObjectType> where ObjectType : ObservableObject

📘 手冊

• SwiftUI ⟩

  • View ⟩ State Modifiers ⟩

    • environmentObject(_:)

  • State and Data Flow ⟩

    • StateObject (struct)

    • ObservedObject (struct)

    • EnvironmentObject (struct)

• Combine ⟩

  • ObservableObject (protocol)

👥 相關

• is Property Wrappers.

• wraps an object that conforms to ObservableObject.

• Binding can be created.