Swinject

Swinject is a lightweight dependency injection framework for Swift.

Dependency injection (DI) is a software design pattern that implements Inversion of Control (IoC) for resolving dependencies. In the pattern, Swinject helps your app split into loosely-coupled components, which can be developed, tested and maintained more easily. Swinject is powered by the Swift generic type system and first class functions to define dependencies of your app simply and fluently.

Swinject is maintained by the Faire Wholesale Inc. mobile platform team.

Features

• [x] Pure Swift Type Support
• [x] Injection with Arguments
• [x] Initializer/Property/Method Injections
• [x] Initialization Callback
• [x] Circular Dependency Injection
• [x] Object Scopes as None (Transient), Graph, Container (Singleton) and Hierarchy
• [x] Support of both Reference and Value Types
• [x] Self-registration (Self-binding)
• [x] Container Hierarchy
• [x] Thread Safety
• [x] Modular Components

Extensions

• SwinjectPropertyLoader: Loading property values from resources.
• SwinjectStoryboard: Automatic dependency injection via Storyboard.
• Swinject-CodeGen: Type-safe code generation of Container from a CSV/YAML file defining dependencies.
• SwinjectAutoregistration: Automatic registration of services by leveraging the Swift Generics.

Requirements

• iOS 11.0+ / Mac OS X 10.13+ / watchOS 4.0+ / tvOS 11.0+
• Xcode 14.3+
• Swift 4.2+
• Carthage 0.18+ (if you use)
• CocoaPods 1.1.1+ (if you use)

Installation

Swinject is available through Carthage, CocoaPods, or Swift Package Manager.

Carthage

To install Swinject with Carthage, add the following line to your Cartfile.

github "Swinject/Swinject"

# Uncomment if you use SwinjectStoryboard
# github "Swinject/SwinjectStoryboard"

Then run carthage update --no-use-binaries command or just carthage update. For details of the installation and usage of Carthage, visit its project page.

CocoaPods

To install Swinject with CocoaPods, add the following lines to your Podfile.

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '11.0' # or platform :osx, '10.13' if your target is OS X.
use_frameworks!

pod 'Swinject'

# Uncomment if you use SwinjectStoryboard
# pod 'SwinjectStoryboard'

Then run pod install command. For details of the installation and usage of CocoaPods, visit its official website.

Swift Package Manager

in Package.swift add the following:

dependencies: [
    // Dependencies declare other packages that this package depends on.
    // .package(url: /* package url */, from: "1.0.0"),
    .package(url: "https://github.com/Swinject/Swinject.git", from: "2.8.0")
],
targets: [
    .target(
        name: "MyProject",
        dependencies: [..., "Swinject"]
    )
    ...
]

Documentation

• Technical documents including patterns of dependency injection and examples.
• API reference

Basic Usage

First, register a service and component pair to a Container, where the component is created by the registered closure as a factory. In this example, Cat and PetOwner are component classes implementing Animal and Person service protocols, respectively.

let container = Container()
container.register(Animal.self) { _ in Cat(name: "Mimi") }
container.register(Person.self) { r in
    PetOwner(pet: r.resolve(Animal.self)!)
}

Then get an instance of a service from the container. The person is resolved to a pet owner, and playing with the cat named Mimi!

let person = container.resolve(Person.self)!
person.play() // prints "I'm playing with Mimi."

Where definitions of the protocols and classes are

protocol Animal {
    var name: String? { get }
}

class Cat: Animal {
    let name: String?

    init(name: String?) {
        self.name = name
    }
}

and

protocol Person {
    func play()
}

class PetOwner: Person {
    let pet: Animal

    init(pet: Animal) {
        self.pet = pet
    }

    func play() {
        let name = pet.name ?? "someone"
        print("I'm playing with \(name).")
    }
}

Notice that the pet of PetOwner is automatically set as the instance of Cat when Person is resolved to the instance of PetOwner. If a container already set up is given, you do not have to care what are the actual types of the services and how they are created with their dependency.

Where to Register Services

Services must be registered to a container before they are used. The typical registration approach will differ depending upon whether you are using SwinjectStoryboard or not.

The following view controller class is used in addition to the protocols and classes above in the examples below.

class PersonViewController: UIViewController {
    var person: Person?
}

With SwinjectStoryboard

Import SwinjectStoryboard at the top of your swift source file.

import SwinjectStoryboard

Services should be registered in an extension of SwinjectStoryboard if you use SwinjectStoryboard. Refer to the project page of SwinjectStoryboard for further details.

extension SwinjectStoryboard {
    @objc class func setup() {
        defaultContainer.register(Animal.self) { _ in Cat(name: "Mimi") }
        defaultContainer.register(Person.self) { r in
            PetOwner(pet: r.resolve(Animal.self)!)
        }
        defaultContainer.register(PersonViewController.self) { r in
            let controller = PersonViewController()
            controller.person = r.resolve(Person.self)
            return controller
        }
    }
}

Without SwinjectStoryboard

If you do not use SwinjectStoryboard to instantiate view controllers, services should be registered to a container in your application’s AppDelegate. Registering before exiting application:didFinishLaunchingWithOptions: will ensure that the services are setup appropriately before they are used.

class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    let container: Container = {
        let container = Container()
        container.register(Animal.self) { _ in Cat(name: "Mimi") }
        container.register(Person.self) { r in
            PetOwner(pet: r.resolve(Animal.self)!)
        }
        container.register(PersonViewController.self) { r in
            let controller = PersonViewController()
            controller.person = r.resolve(Person.self)
            return controller
        }
        return container
    }()

    func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {

        // Instantiate a window.
        let window = UIWindow(frame: UIScreen.main.bounds)
        window.makeKeyAndVisible()
        self.window = window

        // Instantiate the root view controller with dependencies injected by the container.
        window.rootViewController = container.resolve(PersonViewController.self)

        return true
    }
}

Notice that the example uses a convenience initializer taking a closure to register services to the new instance of Container.

Play in Playground!

The project contains Sample-iOS.playground to demonstrate the features of Swinject. Download or clone the project, run the playground, modify it, and play with it to learn Swinject.

To run the playground in the project, first build the project, then select Editor > Execute Playground menu in Xcode.

Example Apps

Some example apps using Swinject can be found on GitHub.

Blog Posts

The following blog posts introduce the concept of dependency injection and Swinject.

• Dependency Injection Tutorial for iOS: Getting Started by Irina Galata
• Swinject Tutorial for iOS: Getting Started by Gemma Barlow
• iOS Dependency Injection Using Swinject by Ali Akhtar
• DI in iOS: Complete guide by Vitaly Batrakov

Thanks the authors!

Contribution Guide

A guide to submit issues, to ask general questions, or to open pull requests is here.

Question?

• Stack Overflow we are trying to monitor questions tagged swinject

Credits

The DI container features of Swinject are inspired by:

• Ninject - Enkari, Ltd and the Ninject project contributors.
• Autofac - Autofac Project.

and highly inspired by:

• Funq - Daniel Cazzulino.

License

MIT license. See the LICENSE file for details.