Dependency Injection in iOS Apps

Transcript

1. %FQFOEFODZ*OKFDUJPO

   JOJ04"QQT
   @yashigani
   ؔϞό #13
   

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2. yashigani
   @yashigani
   http://yashigani.hatenablog.com
   

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3. 8IBUJT
   %FQFOEFODZ*OKFDUJPO
   

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4. • Depend interface, not depend implementations
   • Make less dependency between components
   • Improve testability
   • Make easy to mock dependency objects
   

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5. )PXUPJOKFDU
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6. // Constructor injection
   class ViewController: UIViewController {
   let client: APIClient
   init(client: APIClient) {
   self.client = APIClient
   }
   }
   

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7. • Pros
   • Easy to control
   • Cons
   • Don’t fit storyboard
   • Need dependency objects to create
   

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8. // Property injection
   override func prepareForSegue() {
   if let vc =
   segue.dVC as? NextViewController
   {
   vc.client = client
   }
   }
   

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9. • Pros
   • Don’t need to dependency objects to create
   • Fit view controller with storyboard
   • Cons
   • Too difficult to stay simple
   • Overtime pass to dependency objects
   

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10. // Hold all dependency objects in app
    class Context {
    // Singleton!!!
    private static let context = Context()
    static func get() -> Context {
    return context
    }
    let client = APIClient()
    }
    class ViewController: UIViewController {
    // Depend to singleton pattern
    let context = Context.get()
    }
    

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12. 6TJOH
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13. View Controller
    Context
    

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14. View Controller
    ViewController:
    WithContext
    WithContext
    Context
    ContextType
    

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15. // protocol for Context
    protocol ContextType {
    var client: APIClientType { get }
    }
    class Context: ContextType {
    private static let context = Context()
    static func get() -> Context {
    return context
    }
    let client: APIClientType
    = APIClient()
    }
    

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16. protocol WithContext {
    var context: ContextType { get }
    }
    extension WithContext {
    var context: ContextType {
    return Context.get()
    }
    }
    class ViewController:
    UIViewController, WithContext {}
    

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17. • Default behavior, WithContext return static Context
    object
    • In unit test, add extension ViewController.context
    • Change context object to mock
    • Easy to mock context because it depend to
    ContextType
    • Solve strong dependency to singleton pattern
    

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18. 3FDBQ
    

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19. • Don’t depend to implementations, depend to
    protocols
    • DI makes easy and flexible to inject dependency
    objects
    • Depending protocols makes easy to change
    implementations
    • Fit View Controller with storyboard very much ✨
    

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20. 5IBOLZPV
    

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