Dependency Injection FTW

cocoaheadsNL@Utrecht/Atos

Transcript

1. Dependency Injection FTW
   Ievgen Solodovnykov
   @0xc010d
   

   View Slide

2. I…
   • work at 2dehands.be
   • do iOS stuff during the daylight
   

   View Slide

3. Inversion of Control
   • M. Fowler, 1988 (http://martinfowler.com/bliki/
   InversionOfControl.html)
   • Don't call us, we'll call you
   • Dependency Injection is one of possible
   implementations
   

   View Slide

4. Dependency Injection
   • M. Fowler, 2004 (http://www.martinfowler.com/
   articles/injection.html)
   • Helps to get rid of hard coupling
   • Easier unit testing and motivates to write testable
   code
   • Improves modularity and reusability
   

   View Slide

5. Dependency Injection
   • Constructor injection
   • Property injection
   • Interface injection
   + Automatic injection
   

   View Slide

6. Constructor injection
   @interface APIClient : NSObject
   - (void)loadDataWithCompletionBlock:(void(^)(NSError *))block;
   @end
   !
   //...
   !
   @implementation ViewController {
   APIClient *_apiClient;
   }
   !
   - (instancetype)initWithAPIClient:(APIClient *)apiClient {
   self = [super init];
   _apiClient = apiClient;
   return self;
   }
   !
   - (void)viewDidLoad {
   [super viewDidLoad];
   [_apiClient loadDataWithCompletionBlock:^(NSError *) {
   //...
   }];
   }
   !
   @end
   

   View Slide

7. Property injection
   @interface ViewController : UIViewController
   !
   @property (nonatomic, weak) APIClient *apiClient;
   !
   @end
   !
   //...
   !
   @implementation ViewController
   !
   - (void)viewDidLoad {
   [super viewDidLoad];
   [self.apiClient loadDataWithCompletionBlock:^(NSError *) {
   //...
   }];
   }
   !
   @end
   

   View Slide

8. Method injection
   @implementation ViewController
   !
   - (void)viewDidLoad {
   [super viewDidLoad];
   [self loadDataWithAPIClient:[[APIClient alloc] init]];
   }
   !
   - (void)loadDataWithAPIClient:(APIClient *)apiClient {
   [apiClient loadDataWithCompletionBlock:^(NSError *) {
   //...
   }];
   }
   !
   @end
   

   View Slide

9. Automatic injection with
   BloodMagic
   • https://github.com/railsware/BloodMagic
   • Runtime-based
   • Less code
   • Custom initializers
   • And more…
   

   View Slide

10. BMLazy
    @interface ViewController ()
    !
    @property (nonatomic, weak) APIClient *apiClient;
    !
    @end
    !
    !
    @implementation ViewController
    !
    @dynamic apiClient;
    !
    - (void)viewDidLoad {
    [super viewDidLoad];
    [self.apiClient loadDataWithCompletionBlock:^(NSError *) {
    //...
    }];
    }
    !
    @end
    

    View Slide

11. BMLazy
    [[APIClient alloc] init]
    @interface ViewController ()
    !
    @property (nonatomic, weak) APIClient *apiClient;
    !
    @end
    !
    !
    @implementation ViewController
    !
    @dynamic apiClient;
    !
    - (void)viewDidLoad {
    [super viewDidLoad];
    [self.apiClient loadDataWithCompletionBlock:^(NSError *) {
    //...
    }];
    }
    !
    @end
    

    View Slide

12. Custom initializer
    __attribute__((constructor)) void configureAPIClient(void) {
    BMInitializer *initializer = [BMInitializer lazyInitializer];
    initializer.propertyClass = [APIClient class];
    initializer.initializer = ^id (id sender) {
    static dispatch_once_t onceToken;
    static APIClient *client;
    dispatch_once(&onceToken, ^{
    client = [[APIClient alloc] init];
    });
    return client;
    };
    [initializer registerInitializer];
    }
    

    View Slide

13. Custom initializer
    {
    static dispatch_once_t onceToken;
    static APIClient *client;
    dispatch_once(&onceToken, ^{
    client = [[APIClient alloc] init];
    });
    return client;
    };
    @interface ViewController ()
    !
    @property (nonatomic, weak) APIClient *apiClient;
    !
    @end
    !
    !
    @implementation ViewController
    !
    @dynamic apiClient;
    !
    - (void)viewDidLoad {
    [super viewDidLoad];
    [self.apiClient loadDataWithCompletionBlock:^(NSError *) {
    //...
    }];
    }
    !
    @end
    

    View Slide

14. Protocol binding
    @protocol APICLient
    !
    - (void)loadDataWithCompletionBlock:(void (^)(NSError *))completionBlock;
    !
    @end
    !
    //---
    !
    @interface ProductionAPIClient : NSObject @end
    !
    //---
    !
    @interface ViewController ()
    !
    @property (nonatomic, weak) id apiClient;
    !
    @end
    !
    //---
    !
    @dynamic apiClient;
    !
    - (void)viewDidLoad {
    [super viewDidLoad];
    [self.apiClient loadDataWithCompletionBlock:^(NSError *) {
    //...
    }];
    }
    

    View Slide

15. Protocol initializer
    __attribute__((constructor)) void configureProductionAPIClient(void) {
    BMInitializer *initializer = [BMInitializer lazyInitializer];
    initializer.protocols = @[ @protocol(APICLient) ];
    initializer.initializer = ^id (id sender){
    static dispatch_once_t onceToken;
    static ProductionAPIClient *client;
    dispatch_once(&onceToken, ^{
    client = [[ProductionAPIClient alloc] init];
    });
    return client;
    };
    [initializer registerInitializer];
    }
    !
    

    View Slide

16. Container initializer
    @interface DemoViewController : ViewController @end
    !
    @interface DemoAPIClient : NSObject @end
    !
    __attribute__((constructor)) void configureDemoAPIClient(void) {
    BMInitializer *initializer = [BMInitializer lazyInitializer];
    initializer.protocols = @[ @protocol(APICLient) ];
    initializer.containerClass = [DemoViewController class];
    initializer.initializer = ^id (id sender){
    static dispatch_once_t onceToken;
    static DemoAPIClient *client;
    dispatch_once(&onceToken, ^{
    client = [[DemoAPIClient alloc] init];
    });
    return client;
    };
    [initializer registerInitializer];
    }
    

    View Slide

17. Disadvantages
    • Runtime injecting requires time
    • Runtime errors
    • Requires some intelligence
    

    View Slide

18. Alternatives
    • Typhoon (http://www.typhoonframework.org)
    • Objection (http://objection-framework.org)
    • Xider a.k.a LightMagic (@0xc010d)
    

    View Slide

19. Xider vs BloodMagic
    • Almost as fast as ivar assignment
    • Less flexible implementation :(
    

    View Slide

20. Unit testing
    / with BloodMagic
    

    View Slide

21. Return value tests
    • Works fine with functions, often doesn’t require
    injection
    • Call function/method with different parameters
    • Assert return value
    

    View Slide

22. State tests
    • Might require injection
    • Setup object
    • Call method
    • Assert object property / other method return
    value
    

    View Slide

23. Interaction tests
    • Most often requires injection
    • Setup object
    • Call method
    • Assert other object property / method return
    value
    

    View Slide

24. Demo
    

    View Slide

25. Thank you!
    https://speakerdeck.com/0xc010d/dependency-injection-ftw
    @0xc010d
    

    View Slide