Swinject - Dependency Injection in iOS

In this lecture we'll dive together into how simple and straightforward it is to use dependency injection to clean up your classes, make sure your classes remain as easy-to-test as possible while truly embracing protocol oriented programming.

Transcript

1. Dependency Injection in iOS with Swinject by Oron Ben Zvi
2. Mobile Architect @Gett iOS Developer Fullstack Web Developer DevOps Engineer Oron Ben Zvi oronbz
4. What’s wrong with this code? class WeatherViewController: UIViewController { func load() { let weatherService = WeatherService.sharedInstance weatherService.loadData { ... } } }
5. What’s wrong with this code? class WeatherViewController: UIViewController { func load() { let weatherService = WeatherService.sharedInstance weatherService.loadData { ... } } }
6. What is dependency injection? In software engineering, dependency injection is a technique whereby one object supplies the dependencies of another object. - Wikipedia Another Object Object Dependencies
7. But… What is a dependency? A dependency is an object that your class under test interacts with. Unit Test Class D1 D2 D3 Test
8. A real world example Guy under test
9. A real world example Guy under test Evaluates The tester
10. A real world example Guy under test Evaluates The tester Needs The dependency
11. A real world example Creates The tester The dependency
12. A real world example Creates The tester The dependency Guy under test Passes it to (Injecting) Interacts With
13. Service Locator (is not DI) Locator Class A Uses Service A Service B Locates Locates
14. Service Locator class ServiceLocator { static let sharedInstance = ServiceLocator() func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } // other services } class WeatherViewController: UIViewController { func load() { let weatherService = ServiceLocator.sharedInstance.weatherService weatherService.loadData { ... } } }
15. Service Locator class ServiceLocator { static let sharedInstance = ServiceLocator() func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } // other services } class WeatherViewController: UIViewController { func load() { let weatherService = ServiceLocator.sharedInstance.weatherService weatherService.loadData { ... } } }
16. Why it’s an Anti-Pattern? class ServiceLocator { static let sharedInstance = ServiceLocator() func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } // other services } class WeatherViewController: UIViewController { func load() { let weatherService = ServiceLocator.sharedInstance.weatherService weatherService.loadData { ... } } }
17. Why it’s an Anti-Pattern? class ServiceLocator { static let sharedInstance = ServiceLocator() func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } // other services } class WeatherViewController: UIViewController { func load() { let weatherService = ServiceLocator.sharedInstance.weatherService weatherService.loadData { ... } } }
18. Why it’s an Anti-Pattern? class ServiceLocator { static let sharedInstance = ServiceLocator() func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } // other services } class WeatherViewController: UIViewController { func load() { let weatherService = ServiceLocator.sharedInstance.weatherService weatherService.loadData { ... } } }
19. Why it’s an Anti-Pattern? class ServiceLocator { static let sharedInstance = ServiceLocator() func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } // other services } class WeatherViewController: UIViewController { func load() { let weatherService = ServiceLocator.sharedInstance.weatherService weatherService.loadData { ... } } }
20. Dependency Injection Patterns Extract and Override injection Method injection Property injection Constructor injection
21. Extract and Override Injection class WeatherViewController: UIViewController { func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } func load() { let weatherService = weatherService() weatherService.loadData { ... } } }
22. Method Injection class WeatherViewController: UIViewController { func load(weatherService: WeatherServicing) { weatherService.loadData { ... } } }
23. Property Injection class WeatherViewController: UIViewController { var weatherService: WeatherServicing? func load() { weatherService?.loadData { ... } } }
24. Constructor (Initializer) Injection class WeatherViewController: UIViewController { var weatherService: WeatherServicing init(weatherService: WeatherServicing) { self.weatherService = weatherService } func load() { weatherService.loadData { ... } } }
25. So who does create objects? • Creates UI & business logic objects • Inject dependencies • UI & business logic classes don’t know about assembly Assembly
26. Assembly class WeatherViewController: UIViewController { init(weatherService: WeatherServicing) {...} } ... class Assembly { func weatherService() -> WeatherServicing { return WeatherService.sharedInstance } func weatherViewController() -> WeatherViewController { return WeatherViewController( weatherService: weatherService()) } }
27. Where assembly starts? class AppDelegate: UIResponder, UIApplicationDelegate { private let assembly = Assembly() func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: ...) -> Bool { ... window?.rootViewController = assembly.weatherViewController() ... } }
28. Assembly • How would you handle transitions from controller A to B? • Who creates controller B? • How would you give different implementations for different classes? • How to initialize controllers from storyboards? • Who decide the object scopes (singleton, multiple instances)?
29. Swinject Swinject is a lightweight dependency injection framework for Swift.
30. Swinject Basics protocol Person { var name: String { get } } class PetOwner: Person { let name: String let pet: Animal init(name: String, pet: Animal) { self.name = name self.pet = pet } } protocol Animal { var name: String { get } } class Cat: Animal { let name: String init(name: String) { self.name = name } }
31. Swinject Basics let container = Container() container.register(Animal.self) { _ in Cat(name: "Mimi") } container.register(Person.self) { r in PetOwner(name: "Stephen", pet: r.resolve(Animal.self)!) }
32. Swinject Basics let animal = container.resolve(Animal.self)! let person = container.resolve(Person.self)! let pet = (person as! PetOwner).pet print(animal.name) // prints "Mimi" print(animal is Cat) // prints "true" print(person.name) // prints "Stephen" print(person is PetOwner) // prints "true" print(pet.name) // prints "Mimi" print(pet is Cat) // prints "true"
33. Named Registrations let container = Container() container.register(Animal.self, name: "cat") { _ in Cat(name: "Mimi") } container.register(Animal.self, name: "dog") { _ in Dog(name: "Hachi") }
34. Named Registrations let cat = container.resolve(Animal.self, name:"cat")! let dog = container.resolve(Animal.self, name:"dog")! print(cat.name) // prints "Mimi" print(cat is Cat) // prints "true" print(dog.name) // prints "Hachi" print(dog is Dog) // prints "true"
35. Registration with arguments container.register(Animal.self) { _, name in Horse(name: name) } container.register(Animal.self) { _, name, running in Horse(name: name, running: running) }
36. Registration with arguments let animal1 = container.resolve(Animal.self, argument: "Spirit")! print(animal1.name) // prints "Spirit" print((animal1 as! Horse).running) // prints “false" let animal2 = container.resolve(Animal.self, arguments: "Lucky", true)! print(animal2.name) // prints "Lucky" print((animal2 as! Horse).running) // prints "true"
37. Dependency Injection Patterns Extract and Override injection Method injection Property injection Constructor injection
38. Method Injection let container = Container() container.register(Animal.self) { _ in Cat() } container.register(Person.self) { r in let owner = PetOwner3() owner.setPet(r.resolve(Animal.self)!) return owner }
39. Property Injection let container = Container() container.register(Animal.self) { _ in Cat() } container.register(Person.self) { r in let owner = PetOwner2() owner.pet = r.resolve(Animal.self) return owner }
40. Constructor Injection let container = Container() container.register(Animal.self) { _ in Cat() } container.register(Person.self) { r in PetOwner(pet: r.resolve(Animal.self)!) }
41. Scopes Object scope is a configuration option to determine how an instance provided by a DI container is shared in the system.
42. Transient Class A Service A Service A Different instances Class B
43. Graph (default) Service B Service A Class A Same instance provided for both Class A and Service B Class B Service A Different instances
44. Container (Singleton) Service B Class A Single instance to rule them all Class B Service A
45. Weak Service B Class A Single instance to rule them all Until there are no longer strong references Class B Service A
46. Back to our example // inside AppDelegate didFinishLaunching let container = Container() container.register(WeatherServicing.self) { _ in WeatherService() } .inObjectScope(.container) // singleton container.register(UIViewController.self, name: "WeatherVC") { r in let weatherService = r.resolve(WeatherServicing.self)! return WeatherViewController(weatherService: weatherService) } let weatherVC = container.resolve(UIViewController.self, name: "WeatherVC") window?.rootViewController = weatherVC
47. Storyboards ➕
48. Swinject Storyboard extension SwinjectStoryboard { @objc class func setup() { defaultContainer.storyboardInitCompleted(WeatherViewController.self) { r, c in c.weatherService = r.resolve(WeatherServicing.self) } defaultContainer.register(WeatherServicing.self) { _ in WeatherService() }.inObjectScope(.container) } }
49. Worthy Mentions Typhoon: https://github.com/appsquickly/Typhoon Dip: https://github.com/AliSoftware/Dip
50. Where to go next? RxGitHub: https://github.com/oronbz/RxGithub SwinjectMVVMExample: https://github.com/Swinject/SwinjectMVVMExample Swinject Assembly: https://github.com/Swinject/Swinject/blob/master/Documentation/ Assembler.md Swinject Autoregistration: https://github.com/Swinject/SwinjectAutoregistration