usage-state-dependency.md

State and Dependency Usage

AppState provides powerful tools for managing application-wide state and injecting dependencies into SwiftUI views. By centralizing your state and dependencies, you can ensure your application remains consistent and maintainable.

Overview

• State: Represents a value that can be shared across the app. State values can be modified and observed within your SwiftUI views.
• Dependency: Represents a shared resource or service that can be injected and accessed within SwiftUI views.

Key Features

• Centralized State: Define and manage application-wide state in one place.
• Dependency Injection: Inject and access shared services and resources across different components of your application.

Example Usage

Defining Application State

To define application-wide state, extend the Application object and declare the state properties.

import AppState

struct User {
    var name: String
    var isLoggedIn: Bool
}

extension Application {
    var user: State<User> {
        state(initial: User(name: "Guest", isLoggedIn: false))
    }
}

Accessing and Modifying State in a View

You can access and modify state values directly within a SwiftUI view using the @AppState property wrapper.

import AppState
import SwiftUI

struct ContentView: View {
    @AppState(\.user) var user: User

    var body: some View {
        VStack {
            Text("Hello, \(user.name)!")
            Button("Log in") {
                user.name = "John Doe"
                user.isLoggedIn = true
            }
        }
    }
}

Defining Dependencies

You can define shared resources, such as a network service, as dependencies in the Application object. These dependencies can be injected into SwiftUI views.

import AppState

protocol NetworkServiceType {
    func fetchData() -> String
}

class NetworkService: NetworkServiceType {
    func fetchData() -> String {
        return "Data from network"
    }
}

extension Application {
    var networkService: Dependency<NetworkServiceType> {
        dependency(NetworkService())
    }
}

Accessing Dependencies in a View

Access dependencies within a SwiftUI view using the @AppDependency property wrapper. This allows you to inject services like a network service into your view.

import AppState
import SwiftUI

struct NetworkView: View {
    @AppDependency(\.networkService) var networkService: NetworkServiceType

    var body: some View {
        VStack {
            Text("Data: \(networkService.fetchData())")
        }
    }
}

Combining State and Dependencies in a View

State and dependencies can work together to build more complex application logic. For example, you can fetch data from a service and update the state:

import AppState
import SwiftUI

struct CombinedView: View {
    @AppState(\.user) var user: User
    @AppDependency(\.networkService) var networkService: NetworkServiceType

    var body: some View {
        VStack {
            Text("User: \(user.name)")
            Button("Fetch Data") {
                user.name = networkService.fetchData()
                user.isLoggedIn = true
            }
        }
    }
}

Best Practices

• Centralize State: Keep your application-wide state in one place to avoid duplication and ensure consistency.
• Use Dependencies for Shared Services: Inject dependencies like network services, databases, or other shared resources to avoid tight coupling between components.

Conclusion

With AppState, you can manage application-wide state and inject shared dependencies directly into your SwiftUI views. This pattern helps keep your app modular and maintainable. Explore other features of the AppState library, such as SecureState and SyncState, to further enhance your app's state management.