Dependency Injection FTW

cocoaheadsNL@Utrecht/Atos

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1. Dependency Injection FTW Ievgen Solodovnykov @0xc010d
2. I… • work at 2dehands.be • do iOS stuff during the daylight
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
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
5. Dependency Injection • Constructor injection • Property injection • Interface injection + Automatic injection
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
7. Property injection @interface ViewController : UIViewController ! @property (nonatomic, weak) APIClient *apiClient; ! @end ! //... ! @implementation ViewController ! - (void)viewDidLoad { [super viewDidLoad]; [self.apiClient loadDataWithCompletionBlock:^(NSError *) { //... }]; } ! @end
8. Method injection @implementation ViewController ! - (void)viewDidLoad { [super viewDidLoad]; [self loadDataWithAPIClient:[[APIClient alloc] init]]; } ! - (void)loadDataWithAPIClient:(APIClient *)apiClient { [apiClient loadDataWithCompletionBlock:^(NSError *) { //... }]; } ! @end
9. Automatic injection with BloodMagic • https://github.com/railsware/BloodMagic • Runtime-based • Less code • Custom initializers • And more…
10. BMLazy @interface ViewController () <BMLazy> ! @property (nonatomic, weak) APIClient *apiClient; ! @end ! ! @implementation ViewController ! @dynamic apiClient; ! - (void)viewDidLoad { [super viewDidLoad]; [self.apiClient loadDataWithCompletionBlock:^(NSError *) { //... }]; } ! @end
11. BMLazy [[APIClient alloc] init] @interface ViewController () <BMLazy> ! @property (nonatomic, weak) APIClient *apiClient; ! @end ! ! @implementation ViewController ! @dynamic apiClient; ! - (void)viewDidLoad { [super viewDidLoad]; [self.apiClient loadDataWithCompletionBlock:^(NSError *) { //... }]; } ! @end
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]; }
13. Custom initializer { static dispatch_once_t onceToken; static APIClient *client; dispatch_once(&onceToken, ^{ client = [[APIClient alloc] init]; }); return client; }; @interface ViewController () <BMLazy> ! @property (nonatomic, weak) APIClient *apiClient; ! @end ! ! @implementation ViewController ! @dynamic apiClient; ! - (void)viewDidLoad { [super viewDidLoad]; [self.apiClient loadDataWithCompletionBlock:^(NSError *) { //... }]; } ! @end
14. Protocol binding @protocol APICLient <NSObject> ! - (void)loadDataWithCompletionBlock:(void (^)(NSError *))completionBlock; ! @end ! //--- ! @interface ProductionAPIClient : NSObject <APICLient> @end ! //--- ! @interface ViewController () <BMLazy> ! @property (nonatomic, weak) id<APICLient> apiClient; ! @end ! //--- ! @dynamic apiClient; ! - (void)viewDidLoad { [super viewDidLoad]; [self.apiClient loadDataWithCompletionBlock:^(NSError *) { //... }]; }
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]; } !
16. Container initializer @interface DemoViewController : ViewController @end ! @interface DemoAPIClient : NSObject <APICLient> @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]; }
17. Disadvantages • Runtime injecting requires time • Runtime errors • Requires some intelligence
18. Alternatives • Typhoon (http://www.typhoonframework.org) • Objection (http://objection-framework.org) • Xider a.k.a LightMagic (@0xc010d)
19. Xider vs BloodMagic • Almost as fast as ivar assignment • Less flexible implementation :(
20. Unit testing / with BloodMagic
21. Return value tests • Works fine with functions, often doesn’t require injection • Call function/method with different parameters • Assert return value
22. State tests • Might require injection • Setup object • Call method • Assert object property / other method return value
23. Interaction tests • Most often requires injection • Setup object • Call method • Assert other object property / method return value
24. Demo
25. Thank you! https://speakerdeck.com/0xc010d/dependency-injection-ftw @0xc010d