Protocol Oriented Programming

Talk from CocoaHeads Kraków January 2016.

Transcript

1. Protocol Oriented Programming In Swift 21.01.2016 1 RADEK CIĘCIWA @RADEKCIECIWA
2. 2 PROTOCOL ORIENTED PROGRAMING
3. 3 1. Intro to protocols 2. Protocols application 3. P.O.P. & new swift protocols tricks 4. Summary Agenda
4. 4 Contracts Interfaces Behaviours What Are Protocols?
5. 5 Obj-C @protocol Engineer <NSObject> Swift protocol Engineer What Are Protocols?
6. WHY OBJ-C PROTOCOLS SHOULD EXTEND <NSOBJECT> PROTOCOL?
7. 7 Class consist of Type Behaviour State Let’s Take A Close Look To Class
8. 8 class Engineer { func readSpecification() {} func writeCode() -> Codebase { … } private func drinkCoffee() { } private func copyFromStackoverflow () -> Codebase { … } } Let’s Take A Close Look To Class
9. 9 protocol Engineer { func readSpecification() func writeCode() -> Codebase } Let’s Take A Close Look To Class
10. 10 class BeginnerEngineer: Engineer { func readSpecification() { … } // need to be implemented func writeCode() -> Codebase { … } // need to be implemented func learn() { … } private func drinkCoffee() { … } private func copyFromStackoverflow () -> Codebase { … } } Let’s Take A Close Look To Class
11. 11 struct ProductOwner { let engineer: Engineer // see only those 2 declared methods public func createAwesomeProduct() -> Product { engineer.writeCode() // coupled to behaviour not class drinkCoffee() } private func drinkCoffee() { } } Let’s Take A Close Look To Class
12. PROTOCOL APLICATIONS
13. 13 class Analytics { let kiss: KissMetricsLibrary let googleAnalytics: GoogleAnalyticsLibrary func sendEvent(event: Event) { ... } } Our Protocol Adaptation - Part 1
14. 14 func sendEvent(event: Event) { kiss.sendKissEvent(event) googleAnalytics.sendGoogleEvent(event) } Our Protocol Adaptation - Part 1
15. 15 func sendEvent(event: Event) { kiss.sendKissEvent(event) googleAnalytics.sendGoogleEvent(event) apptentive.sendEvent(event) branch.sendEvent(event) } Our Protocol Adaptation - Part 1
16. 16 func sendEvent(event: Event) { if FirstTimeChecker.check(event.name) { kiss.sendKissOncePerAppLivetimeEvent(event) } kiss.sendKissEvent(event) googleAnalytics.sendGoogleEvent(event) apptentive.sendEvent(event) branch.sendEvent(event) } Our Protocol Adaptation - Part 1
17. 17 Open-Close principle Objects or entities should be open for extension, but closed for modification. S.O.L.I.D. „O” Principle
18. 18 protocol EventProcessable { func processEvent(event:Event) } Our Protocol Adaptation - Part 1
19. 19 extension KissMetricsLibrary: EventProcessable { func processEvent(event:Event) { … } } or … struct GoogleAnalyticsProcessable: EventProcessable { let ga: GoogleAnalyticsLibrary func processEvent(event:Event) { … } } Our Protocol Adaptation - Part 1
20. 20 struct FirstTimeEventProcessable: EventProcessable { let processable: EventProcessable func processEvent(event:Event) { if FirstTimeChecker.check(event.name) { processable.processOncePerApp(event) } processable.processEvent(event) } } Our Protocol Adaptation - Part 1
21. 21 class Analytics { let processes: [EventProcessable] func sendEvent(event: Event) { for let process in processes { process.processEvent(event) } } } Our Protocol Adaptation - Part 1
22. 22 func sendEvent(event: Event) { for let process in processes { process.sendEvent(event) } } And To Compare… func sendEvent(event: Event) { if FirstTimeChecker.check(event.name) { kiss.sendKissOncePerAppLivetimeEvent(event) } kiss.sendKissEvent(event) googleAnalytics.sendGoogleEvent(event) apptentive.sendEvent(event) branch.sendEvent(event) }
23. 23 We want to NSLog all events that are send to Analytics New Requirement
24. 24 struct PrintProcess: EventProcessable { func processEvent(event:Event) { NSLog(event) } } class Analytics { let processes: [EventProcessable] // += PrintProcess Our Protocol Adaptation - Part 1
25. DO SWIFT PROTOCOLS HAVE OPTIONAL METHODS?
26. 26 struct APIClient { func requestForData(completion: ([FacebookPost])->()) { … } } Mocking With Protocols
27. 27 class PostsViewController: UIViewController { private let client: APIClient func viewDidLoad() { client.requestForData() { (listOfPosts: [FacebookPost]) in populate(listOfPosts) } } } Mocking With Protocols
28. 28 protocol FacebookPostsRepository { func getPosts(completion: ([FacebookPost])->()) } struct APIClientFacebookPostsRepository: FacebookPostsRepository { let client: APIClient func getPosts(completion: ([FacebookPost])->()) { client.requestForData(completion) } } or more preferred extension APIClient: FacebookPostsRepository Mocking With Protocols
29. 29 class PostsViewController: UIViewController { private let repository: FacebookPostsRepository func viewDidLoad() { repository.getPosts() { (listOfPosts: [FacebookPost]) in populate(listOfPosts) } } } Mocking With Protocols
30. 30 struct MockFacebookPostsRepository: FacebookPostsRepository { func getPosts(completion: ([FacebookPost])->()) { completion( createArrayOfPosts() ) } } Mocking With Protocols
31. 31 - Faster development - Customization of Mock object - Definition outside PostsViewController class HINT: It allows you to use AbstractFactory pattern to mock large part of functionality scope. Mocking With Protocols
32. 32 struct Navigation { init(presentable: Presentable, factory: NavigationCreatable) { … } func goToURL(url: NSURL) -> Bool { ... } } Testing With Protocols
33. 33 protocol Presentable { // show view controller func show(viewController: UIViewController, animated: Bool) } protocol NavigationCreatable { // creates view controller from screen name func controllerForPath(screen: String) -> UIViewController? } Testing With Protocols
34. 34 class PresentableSpy: Presentable { var wasUsed = false var capturedController : UIViewController? func show(viewController: UIViewController, animated: Bool) { wasUsed = true capturedController = viewController } } Testing With Protocols
35. 35 class NavigationTests: XCTestCase { var sut: Navigation! var presentableSpy: PresentableSpy! // the same for CreatableSpy override func setUp() { super.setUp() presentableSpy = PresentableSpy() sut = Navigation(presentable: presentableSpy, factory: creatableSpy) } Testing With Protocols
36. 36 func testIfPresentableWasUsedIfReturnedTrue() { let didHandle = sut.goToURL(NSURL(string: "brainly://us/fixture/42")!) XCTAssertTrue(didHandle) XCTAssertTrue(presentableSpy.wasUsed) } func testIfWeCreateControllerWithDetails() { sut.goToURL(NSURL(string: "brainly://us/fixture/42")!) XCTAssertTrue(navigationCreatableSpy.wasUsed) XCTAssertEqual("fixture", navigationCreatableSpy.capturedScreen) // fixture should be name of screen } Testing With Protocols
37. 37 NavigationRouter class requirements - switch between loading and main app screens - handle url links to app - creating and displaying UIViewControllers (modally with custom transition) - switching between ‘tab’ like screen in app Only 200 loc (but strongly coupled code) Coupled with custom classes. Not easy to extend e.g. on iPad Extracting Code From God Classes
38. P.O.P.
39. DO PROTOCOLS CAN HAVE IMPLEMENTATIONS?
41. 41 Principles Of P.O.P. From KrakenDev: „At the heart of Protocol Oriented Programming is abstraction & simplicity.” 1. Start with protocol 2. Use Value Types
42. 42 Principles Of P.O.P. Object Oriented Principles: Abstraction Polymorphism Encapsulation Inheritance
43. 43 Value types, is a type whose value is copied when it is assigned to a variable or constant, or when it is passed to a function. This reduces complexity by only having one owner at any point in time Value Types Vs Reference Types
44. 44 Requirement: Neatly handle errors. So, let’s create UIAlertView. Principles Of P.O.P.
45. 45 class ErrorHandler { class func handleError(error: NSError) { let alert = UIAlertView(title: description, message: reason, delegate: nil, cancelButtonTitle: "OK") alert.show() } } Principles Of P.O.P.
46. 46 client.requestForData() { (listOfPosts: [FacebookPost]) in populate(listOfPosts) }, failure: { [weak self] (error: NSError!) -> Void in ErrorHandler.handleError(error) } Principles Of P.O.P.
47. 47 protocol ErrorHandable { func handleError(error: NSError) } extension ErrorHandable { func handleError(error: NSError) { let alert = UIAlertView(title: description, message: reason, delegate: nil, cancelButtonTitle: "OK") alert.show() } } Default Implementation
48. 48 class PostsViewController: UIViewController, ErrorHandable { func viewDidLoad() { client.requestForData() { (listOfPosts: [FacebookPost]) in populate(listOfPosts) }, failure: { [weak self] (error: NSError!) -> Void in self?.handleError(error) } } } Default Implementation
49. 49 class DetailViewController: UIViewController, ErrorHandable { func handleError(error: NSError) { // custom error handle } } Default Implementation
50. 50 extension ErrorHandable { func handleError(error: NSError) { let alert = UIAlertView(title: description, message: reason, delegate: nil, cancelButtonTitle: "OK") alert.show() } } Principles Of P.O.P. !!! “Important: UIAlertView is deprecated in iOS 8.” So probably it’s time to swap to: “UIAlertController”
51. 51 extension ErrorHandable { func handleError(error: NSError) { let alert = UIAlertController(title: description, message: reason, preferredStyle: .Alert) self.presentViewController(alert, animated: true, completion: nil) } } Principles Of P.O.P. !!! Type „ErrorHandler” has no member presentViewController
52. 52 extension ErrorHandable where Self: UIViewController { func handleError(error: NSError) { let alert = UIAlertController(title: description, message:reason, preferredStyle: .Alert) self.presentViewController(alert, animated: true, completion: nil) } } Principles Of P.O.P.
53. 53 Let’s Get Back To Start
54. 54 protocol Engineer { func readSpecification() func writeCode() -> Codebase } Let’s Get Back To Start
55. 55 extension Engineer where Self: CorporateDeveloper { func readSpecification() { let fourtyTwoPagesSpecification = repository.getSpecification() // Even the variable name is long read(fourtyTwoPagesSpecification) } } Let’s Get Back To Start
56. 56 struct CorporateDeveloper: Engineer { } Let’s Get Back To Start Error: Type ‘CorporateDeveloper’ does not conform to protocol ‘Engineer’
57. 57 struct CorporateDeveloper: Engineer { func writeCode() -> Codebase { … } } Let’s Get Back To Start // It's ok now
58. 58 protocol Engineer { func canDoPairProgramming(secondEng: Engineer) -> Bool } Self Requirement
59. 59 struct CorporateDeveloper: Engineer { let departmentName: String func canDoPairProgramming(secondEng: Engineer) -> Bool { return departmentName == secondEng.departmentName // Error here } } Self Requirement
60. 60 struct CorporateDeveloper: Engineer { let departmentName: String func canDoPairProgramming(secondEng: Engineer) -> Bool { return departmentName == (secondEng as! CorporateDeveloper).departmentName } } Self Requirement
61. 61 // with self requirement protocol Engineer { func canDoPairProgramming(secondEng: Self) -> Bool } Self Requirement struct CorporateDeveloper: Engineer { let departmentName: String func canDoPairProgramming(secondEng: CorporateDeveloper) -> Bool { return departmentName == secondEng.departmentName } }
62. 62 // if protocol have Self requirement like this protocol Engineer { func canDoPairProgramming(secondEng: Self) -> Bool } Self Requirement
63. 63 let b: Engineer // !compiler error Self Requirement
64. 64 // use as a generic constraint func lunchTime<T: Engineer>(obj: T) Self Requirement
65. 65 // collections will be always of the same type - homogeneous func lunchTimeEverybody<T: Engineer>(obj: [T]) Self Requirement
66. 66 // generic constraint could have more protocols to conform func lunchTimeEverybody<T where T: Engineer, T: Hungry, T: PizzaFan>(a: T) Self Requirement
67. 67 protocol Engineer { } protocol Hungry { } protocol PizzaFan { } func lunchTimeEverybody<T: protocol<Engineer, Hungry, PizzaFan>>(obj: [T]) Combining Protocols In Swift typealias HungryEngineer = protocol<Engineer, Hungry, PizzaFan> func lunchTimeEverybody<T: HungryEngineer>(guys: [T]) -> Bool { ... }
68. SUMMARY
69. 69 P.O.P Start building with protocol Use protocols to correctly define your entities relationships
70. 70 Why Should I Use Value Types No sharable mutable state (we have copies) Copies are cheap Lanugage mechanisms that enforces immutability
71. 71 If you need shared state of object Where Should I Use Classes UIKit classes inheritence Copying stuff will not fix your architecture
72. GOOD PRACTICES
73. 73 Keep extensions of protocol in the same file (easier to find) Keep extensions of class that conform to protocol in class file Good Practices
74. 74 // !Preferred: class MyViewcontroller: UIViewController { // class stuff here } // MARK: - UITableViewDataSource extension MyViewcontroller: UITableViewDataSource { // table view data source methods } // !Not Preferred: class MyViewcontroller: UIViewController, UITableViewDataSource, UIScrollViewDelegate { // all methods } ref: https://github.com/raywenderlich/swift-style-guide#protocol-conformance Style Guide
75. 75 Default implementations are not transformable to Obj-C Optional methods can’t be applied to structs or enumerations @objc tagged protocols cannot be applied to structs or enumerations Swift Only
76. 76 import Foundation @objc protocol TicketServiceDelegate { optional func ticketServiceStopped(handler: TicketService) } Optional Methods In Swift class TicketService: NSObject { // for Obj-C conformance weak var delegate: TicketServiceDelegate? func stop() { delegate?.ticketServiceStopped?(self) } }
77. THANKS!
78. ANY QUESTIONS ?!