🧠 Effortless Dependency Injection for Swift Applications. Dependency only mirror of AppState

What's New



What's Changed

  • Update by @0xLeif in #6
  • Change logger for linux and windows to var by @0xLeif in #7

Full Changelog: 1.0.0...1.1.0


AppDependency is a Swift Package that simplifies the management of application dependencies in a thread-safe, type-safe, and SwiftUI-friendly way. Featuring dedicated struct types for managing dependencies, AppDependency provides easy and coordinated access to dependencies across your application. Added to this, the package incorporates built-in logging mechanisms to aid debugging and error tracking. The AppDependency package also boasts a cache-based system to persistently store and retrieve any application-wide data at any given time.

AppDependency is a dependency only mirror of AppState.

Requirements: iOS 15.0+ / watchOS 8.0+ / macOS 11.0+ / tvOS 15.0+ / visionOS 1.0+ | Swift 5.9+ / Xcode 15+

Non Apple Platform Support: Linux & Windows

Key Features

(🍎 Apple OS only)

Dependency Management

  • Dependency: Struct for encapsulating dependencies within the app's scope.
  • Scope: Represents a specific context within an app, defined by a unique name and ID.

Fine-Grained Control

  • DependencySlice: Struct that provides access to and modification of specific AppDependency's dependency parts.

Property Wrappers

  • AppDependency: Simplifies the handling of dependencies throughout your application.
  • 🍎 ObservedDependency: Simplifies the handling of dependencies throughout your application. Dependencies must conform to ObservableObject. Backed by an @ObservedObject to publish changes to SwiftUI views.
  • DependencySlice: Allows users to access and modify a specific part of AppDependency's dependency.
  • DependencyConstant: Allows users to access a specific part of AppDependency's dependency.

Getting Started

To integrate AppDependency into your Swift project, you'll need to use the Swift Package Manager (SPM). SPM makes it easy to manage Swift package dependencies. Here's what you need to do:

  1. Add a package dependency to your Package.swift file:
dependencies: [
    .package(url: "", from: "1.0.0")

If you're working with an App project, open your project in Xcode. Navigate to File > Swift Packages > Add Package Dependency... and enter

  1. Next, don't forget to add AppDependency as a target to your project. This step is necessary for both Xcode and SPM Package.swift.

After successfully adding AppDependency as a dependency, you need to import AppDependency into your Swift file where you want to use it. Here's a code example:

import AppDependency


Defining Dependencies

Dependency is a feature provided by AppDependency, allowing you to define shared resources or services in your application.

To define a dependency, you should extend the Application object. Here's an example of defining a networkService dependency:

extension Application {
    var networkService: Dependency<NetworkServiceType> {

In this example, Dependency<NetworkServiceType> represents a type safe container for NetworkService.

Reading and Using Dependencies

Once you've defined a dependency, you can access it anywhere in your app:

let networkService = Application.dependency(\.networkService)

This approach allows you to work with dependencies in a type-safe manner, avoiding the need to manually handle errors related to incorrect types.

AppDependency Property Wrapper

AppDependency provides the @AppDependency property wrapper that simplifies access to dependencies. When you annotate a property with @AppDependency, it fetches the appropriate dependency from the Application object directly.

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

    // Your view code

In this case, ContentView has access to the networkService dependency and can use it within its code.

Using Dependency with ObservableObject

When your dependency is an ObservableObject, any changes to it will automatically update your SwiftUI views. Make sure your service conforms to the ObservableObject protocol. To do this, you should not use the @AppDependency property wrapper, but instead use the @ObservedDependency property wrapper.

Here's an example:

class DataService: ObservableObject {
    @Published var data: [String]

    func fetchData() { ... }

extension Application {
    var dataService: Dependency<DataService> {

struct ContentView: View {
    @ObservedDependency(\.dataService) private var dataService

    var body: some View {
        List(, id: \.self) { item in
        .onAppear {

In this example, whenever data in DataService changes, SwiftUI automatically updates the ContentView.

Testing with Mock Dependencies

One of the great advantages of using Dependency in AppDependency is the capability to replace dependencies with mock versions during testing. This is incredibly useful for isolating parts of your application for unit testing.

You can replace a dependency by calling the Application.override function. This function returns a DependencyOverride, you'll want to hold onto this token for as long as you want the mock dependency to be effective. When the token is deallocated, the dependency reverts back to its original condition.

Here's an example:

// Real network service
extension Application {
    var networkService: Dependency<NetworkServiceType> {

// Mock network service
class MockNetworkService: NetworkServiceType {
    // Your mock implementation

func testNetworkService() {
    // Keep hold of the `DependencyOverride` for the duration of your test.
    let networkOverride = Application.override(\.networkService, with: MockNetworkService())

    let mockNetworkService = Application.dependency(\.networkService)
    // Once done, you can allow the `DependencyOverrideen` to be deallocated 
    // or call `networkOverride.cancel()` to revert back to the original service.

SwiftUI Previews

To override a dependency inside a SwiftUI preview, you must use the Environment.preview function and pass in the dependency overrides with the content.

class Service {
    var title: String { "Live Service" }

class MockService: Service {
    override var title: String { "Mock Service" }

extension Application {
    var service: Dependency<Service> {

struct ContentView: View {
    @AppDependency(\.service) private var service

    var body: some View {

#Preview {
        Application.override(\.service, with: MockService()),
        Application.override(\.userDefaults, with: UserDefaults())
    ) {


AppDependency is released under the MIT License. See LICENSE for more information.

Communication and Contribution

  • If you found a bug, open an issue.
  • If you have a feature request, open an issue.
  • If you want to contribute, submit a pull request.


  • Swift Tools 5.9.0
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Last updated: Sun Mar 17 2024 00:11:36 GMT-0900 (Hawaii-Aleutian Daylight Time)