Refactoring iOS Projects - Bangalore

For many developers, refactoring is a menu in their IDE. The truth is that there are tons of refactoring techniques, most of them described in detail by Martin Fowler in his book of that name. In this session we are going to learn simple yet effective techniques to refactor large iOS codebases in order to make them more testable, to adapt them to be eventually rewritten in Swift, and to make them as "future proof" as possible.

Presentation given in Bangalore, India, on September 15th, 2016, at http://www.mobiledevelopersummit.com

Speech: https://akos.ma/blog/refactoring-ios-projects/

Transcript

1. ! !ೕಜ$ಗ& '()ಕ+'ಂ- र ि फ्र ै क्ट र ि ं ग ! प र ि योजनाओं Refactoring ! Projects @akosma – @mobiledevsummit – September 15th 2016 © akosma 2016 1
2. !⌚#$ !ೕಜ$ಗ& '()ಕ+'ಂ- र ि फ्र ै क्ट र ि ं ग !⌚#$ प र ि योजनाओं Refactoring !⌚#$ Projects @akosma – @mobiledevsummit – September 15th 2016 © akosma 2016 2
3. © akosma 2016 3
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5. Thank you ! More information at developer.apple.com © akosma 2016 5
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7. Sorry! ! © akosma 2016 7
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10. Thank you ! More information at jetbrains.com/objc © akosma 2016 10
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12. Seriously? ! © akosma 2016 12
13. Live and Let IDE ! © akosma 2016 13
14. Big Topic ! © akosma 2016 14
15. © akosma 2016 15
16. More ! © akosma 2016 16
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18. Yeah baby !" © akosma 2016 18
19. © akosma 2016 19
20. What is it? ! © akosma 2016 20
21. Refactoring (noun): a change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior. © akosma 2016 21
22. Why to? ! © akosma 2016 22
23. —To improve the design of software —To make it easier to understand —To make it easier to find and fix bugs —To program faster —To annoy your manager © akosma 2016 23
24. When to? ⏰ © akosma 2016 24
25. —When you add features —When fixing bugs —During code reviews © akosma 2016 25
26. When not to? ⛔ © akosma 2016 26
27. © akosma 2016 27
28. 1. Add Tests 2. Refactor © akosma 2016 28
29. © akosma 2016 29
30. © akosma 2016 30
31. How to? ! © akosma 2016 31
32. Bad Smells !68 —Duplicated code —Long methods —Large class —Long parameter list —Divergent change —Shotgun surgery —Feature envy —Data clumps —Primitive obsession —Switch statements —Parallel inheritance hierarchies —Lazy class —Speculative generality —Temporary field —Message chains —Middle Man —Inappropriate intimacy —Alternative classes with different interfaces —Incomplete library class —Data class —Refused bequest —Comments 68 Source: “Refactoring” by Martin Fowler (1999) © akosma 2016 32
33. !⌚#$ Specific Smells ! Swift and Cocoa Smells ! Class Design Smells ! Project Management Smells © akosma 2016 33
34. ! Swift and Cocoa Smells © akosma 2016 34
35. !" SwiftyLeaks © akosma 2016 35
36. © akosma 2016 36
37. Memory Leaks in Swift Reference Cycles23: —Instances —Closures 23 Source: Apple Developer Library © akosma 2016 37
38. Instance Reference Cycles (1/2) class Person { let name: String var apartment: Apartment? } class Apartment { let unit: String var tenant: Person? // Ouch! } © akosma 2016 38
39. © akosma 2016 39
40. Instance Reference Cycles (2/2) class Person { let name: String var apartment: Apartment? } class Apartment { let unit: String weak var tenant: Person? // Yay! } © akosma 2016 40
41. © akosma 2016 41
42. weak vs. unowned —weak can be nil —unowned cannot be nil —unowned ➡ always nonoptional types © akosma 2016 42
43. Closure Reference Cycles (1/2) let obj = SomeObject() obj.blockMember = { return obj.property // Ouch! } © akosma 2016 43
44. Closure Reference Cycles (2/2) let obj = SomeObject() obj.blockMember = { [unowned obj] return obj.property // Yay! } © akosma 2016 44
45. Closures are reference types⾠ © akosma 2016 45
46. !" Hungarian Notation © akosma 2016 46
47. protocol IUnknown { func QueryInterface (_ riid: REFIID, _ ppvObject: LPVOID) -> HRESULT func AddRef() -> ULONG func Release() -> ULONG } protocol IDispatch : IUnknown { func GetTypeInfoCount(pctinfo: UInt) -> HRESULT func GetTypeInfo(_ iTInfo: UInt, _ lcid: LCID, _ ppTInfo: ITypeInfo) -> HRESULT func GetIDsOfNames(_ riid: REFIID, _ rgszNames: OLECHAR, _ cNames: UInt, _ lcid: LCID, _ rgDispId: DISPID) -> HRESULT func Invoke(_ dispIdMember: DISPID, _ riid: REFIID, _ lcid: LCID, _ wFlags: WORD, _ pDispParams: DISPPARAMS, _ pVarResult: VARIANT, _ pExcepInfo: EXCEPINFO, _ puArgErr: UInt32) -> HRESULT } © akosma 2016 47
48. let oPerson = Server.CreateObject("Person") var bBusy = true if (bBusy) { bBusy = false let riid = CFUUIDGetUUIDBytes(CFUUIDCreate(kCFAllocatorDefault)) let ppvObject = UnsafeMutablePointer<Void>(allocatingCapacity: 10) let result = oPerson.QueryInterface(riid, ppvObject) if result == 0x80090032 { bBusy = true oPerson.Invoke(0, riid, riid, 0, riid, nil, nil, 0) } } © akosma 2016 48
49. Programs must be written for people to read, and only incidentally for machines to execute. © akosma 2016 49
50. Swift API design guidelines55 // Make APIs read grammatically friends.remove(ted) mainView.addChild(button, at: origin) truck.removeBoxes(withLabel: "mobiledevsummit") // Use verbs for side effects friends.reverse() viewController.present(animated: true) 55 Source: WWDC 2016 session 403 © akosma 2016 50
51. Swift API design guidelines55 // Use nouns for returned values button.backgroundTitle(for: .disabled) friends.suffix(3) // Mutating and non-mutating method pairs x.reverse() // mutating let y = x.reversed() // non-mutating dir.appendPathComponent(".txt") // mutating let newDir = dir.appendingPathComponent(".txt") // non-mutating 55 Source: WWDC 2016 session 403 © akosma 2016 51
52. Swift 㲗 Objective-C Two different signatures: one for Swift, another for Objective-C @objc() exports Swift API ➡ Objective-C NS_SWIFT_NAME() Objective-C APIs ➡ Swift © akosma 2016 52
53. !" Objective-C Nostalgia © akosma 2016 53
54. Migrate to Swift3 NS_ASSUME_NONNULL_BEGIN #define let __auto_type const #define var __auto_type @property(nonatomic, nonnull, copy) NSString *name; @property(nonatomic, nullable, weak) id<UITableViewDelegate> delegate; - (nullable NSArray *)arrayWithWord:(nonnull NSString *)word { // NSArray<NSString *> * _Nonnull words = @[@"one", @"two", word]; __auto_type _Nonnull words = @[@"one", @"two", word]; return words; } NS_ASSUME_NONNULL_END 3 Source: Swift Blog © akosma 2016 54
55. Caveats —Objective-C cannot subclass a Swift class —…unless marked @objc —Tuples, Swift enums and structs are not accessible from Objective-C. © akosma 2016 55
56. !" Homemade Cache © akosma 2016 56
57. “There are only two hard things in Computer Science: cache invalidation and naming things.” Phil Karlton10 10 Source: Martin Fowler © akosma 2016 57
58. NSURLCache let config = URLSessionConfiguration.default config.requestCachePolicy = .returnCacheDataElseLoad let memoryCapacity = 10 * 1024 * 1024; let diskCapacity = 20 * 1024 * 1024; let cache = URLCache(memoryCapacity: memoryCapacity, diskCapacity: diskCapacity, diskPath: nil) URLCache.shared = cache © akosma 2016 58
59. !" Tagged Views © akosma 2016 59
60. Do not viewWithTag() override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) let object = objects[indexPath.row] as! NSDate cell.textLabel!.text = object.description let switchControl = cell.viewWithTag(1) as! UISwitch // Ouch! switchControl.setOn(false, animated: false) return cell } © akosma 2016 60
61. Custom View Class override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! CustomViewCell let object = objects[indexPath.row] as! NSDate cell.titleLabel.text = object.description cell.switchControl.setOn(true, animated: false) // Yay! return cell } © akosma 2016 61
62. !" Illicit Association © akosma 2016 62
63. Associated Objects 86 extension NSWhatever { private struct Keys { static var Value = "AssociatedValue" } var associatedString: String? { get { return objc_getAssociatedObject(self, &Keys.Value) as? String } set { objc_setAssociatedObject(self, &Keys.Value, newValue as NSString?, .OBJC_ASSOCIATION_COPY_NONATOMIC) } } } var obj = NSWhatever() obj.associatedString = "Some other string" 86 Source: NSHipster © akosma 2016 63
64. Associated Objects 14 Do not if you can use instead: —Subclassing —Target-Action —Gesture recognizers —Delegation —NSNotification 14 Source: NSHipster © akosma 2016 64
65. © akosma 2016 65
66. ! Class Design Smells © akosma 2016 66
67. !" Class Struggle © akosma 2016 67
68. class or struct? ! (1/2) protocol Modifiable { // protocols FTW! var value : Int { get set } mutating func increase() } extension Modifiable { mutating func increase() { value += 100 } } © akosma 2016 68
69. class or struct? ! (2/2) struct TypeOne : Modifiable { var value = 0 } class TypeTwo : Modifiable { var value = 0 } var v1, v2, r1, r2 : Modifiable v1 = TypeOne(); v2 = v1 // Value type, copied r1 = TypeTwo(); r2 = r1 // Reference type, not copied v2.increase(); assert(v1.value != v2.value) r2.increase(); assert(r1.value == r2.value) © akosma 2016 69
70. Reference Types ! —Inheritance —Reference semantics —Use Swift types in Objective-C Value Types ! —Always implement Equatable on your own76 —More testable architectures —Immutable by default 76 Source: WWDC 2015 Session 414 © akosma 2016 70
71. !" Massive View Controller (MVC) and Massive App Delegate (MAD) © akosma 2016 71
72. © akosma 2016 72
73. Class Breakdown ! Maximum 400 lines ! © akosma 2016 73
74. Empty States72 1. First use39 2. User cleared 3. Errors 39 Source: Designing For The Empty States 72 Source: emptystat.es © akosma 2016 74
75. State Machines12 —AppState enumeration with associated lambdas —GKState and GKStateMachine Other Approaches —Model-View-ViewModel (MVVM) —Protocols & Extensions —Dependency Injection —ReSwift, PromiseKit, RxSwift, ReactKit, ReactiveCocoa… 12 Source: Github © akosma 2016 75
76. AppState (1/3) enum AppState { case None case Active(action: Block) // typealias Block = (Void) -> Void case Inactive(action: Block) func execute() { switch self { case .Active(let block): block() case .Inactive(let block): block() default: return } } } © akosma 2016 76
77. AppState (2/3) class SomeController { var state = AppState.None { didSet { state.execute() } } func viewDidLoad() { // ... } © akosma 2016 77
78. AppState (3/3) func viewDidLoad() { super.viewDidLoad() let inactive = AppState.Inactive { [unowned self] () in self.view.backgroundColor = UIColor.red() } let active = AppState.Active { [unowned self] () in self.view.backgroundColor = UIColor.green() } // ... self.state = inactive } © akosma 2016 78
79. GKState and GKStateMachine (1/2) import GameplayKit class ActiveState: GKState { override func isValidNextState(_ stateClass: AnyClass) -> Bool { if stateClass == InactiveState.self { return true } return false } override func didEnter(withPreviousState previousState: GKState?) { // change UI elements, etc, etc... } override func willExit(withNextState nextState: GKState) { // ... } } © akosma 2016 79
80. GKState and GKStateMachine (2/2) let active = ActiveState() let inactive = InactiveState() let stateMachine = GKStateMachine(states: [active, inactive]) stateMachine.enterState(InactiveState.self) © akosma 2016 80
81. © akosma 2016 81
82. Model – View – ViewModel (MVVM 1/2) class DetailViewModel: NSObject { let model : Model init(withModel model: Model) { self.model = model } var displayText : String { return self.model.description } } © akosma 2016 82
83. Model – View – ViewModel (MVVM 2/2) class DetailViewController: UIViewController { @IBOutlet weak var label: UILabel! var viewModel : DetailViewModel? override func viewDidLoad() { super.viewDidLoad() self.label.text = self.viewModel?.displayText } } © akosma 2016 83
84. Martin Fowler Says68 —Extract Class (149) —Extract Subclass (330) —Extract Interface (341) —Duplicate Observed Data (189) 68 Source: “Refactoring” by Martin Fowler (1999) © akosma 2016 84
85. Learn more about MVVM "MVVM-C In Practice" Tomorrow 13:50, by Steve Scott, in the Main Hall © akosma 2016 85
86. Learn more about React "React Native for Android" Today 17:10, by Anirudh Sundararaman, in the SD Hall © akosma 2016 86
87. !" Forgotten Memory Warnings © akosma 2016 87
88. Memory Warnings func applicationDidReceiveMemoryWarning(_ application: UIApplication) { // ... on the app delegate... } override func didReceiveMemoryWarning() { super.didReceiveMemoryWarning() // ... on every controller... } // ... and anywhere else let center = NotificationCenter.default() let notification = NSNotification.Name.UIApplicationDidReceiveMemoryWarning let selector = #selector(SomeClass.handler(_:)) center.addObserver(self, selector: selector, name: notification, object: nil) © akosma 2016 88
89. Lazy Loading Class class LazyLoader { var _backingField: String? var property: String? { get { if _backingField == nil { _backingField = "text" } return _backingField } set { _backingField = newValue } } } © akosma 2016 89
90. !" Long Switch Statement © akosma 2016 90
91. Pattern Matching44 switch (indexPath.section, indexPath.row) { case (0, let row): cell.backgroundColor = UIColor.lightGray() // ... case (let section, 0) where section % 2 == 0: cell.backgroundColor = UIColor.brown() // ... case let (3, row) where validate(row): cell.backgroundColor = UIColor.blue() // ... default: cell.backgroundColor = UIColor.white() } 44 Source: Ash Furrow © akosma 2016 91
92. Martin Fowler Says68 —Extract Method (110) —Move Method (142) —Replace Type Code With Subclasses (223) —Replace Type Code With State/Strategy (227) —Replace Conditional with Polymorphism (255) 68 Source: “Refactoring” by Martin Fowler (1999) © akosma 2016 92
93. !" Long Method Names © akosma 2016 93
94. “There are only two hard things in Computer Science: cache invalidation and naming things.” Phil Karlton10 10 Source: Martin Fowler © akosma 2016 94
95. Cocoa Awards™ ! © akosma 2016 95
96. Cocoa Awards™ ! Longest Method Name Category95 95 Source: Quora and Github © akosma 2016 96
97. …and the winner is… // QCPlugInContext class - (id) outputImageProviderFromBufferWithPixelFormat:(NSString*)format pixelsWide:(NSUInteger)width pixelsHigh:(NSUInteger)height baseAddress:(const void*)baseAddress bytesPerRow:(NSUInteger)rowBytes releaseCallback:(QCPlugInBufferReleaseCallback)callback releaseContext:(void*)context colorSpace:(CGColorSpaceRef)colorSpace shouldColorMatch:(BOOL)colorMatch; © akosma 2016 97
98. © akosma 2016 98
99. Martin Fowler Says68 —Replace Parameter with Method (292) —Preserve Whole Object (288) —Introduce Parameter Object (295) 68 Source: “Refactoring” by Martin Fowler (1999) © akosma 2016 99
100. Parameter Objects in Cocoa // Map snapshots let options = MKMapSnapshotOptions() options.region = mapView.region options.size = mapView.frame.size let snapshotter = MKMapSnapshotter(options: options) // URL Sessions let config = URLSessionConfiguration() config.httpShouldSetCookies = false config.timeoutIntervalForRequest = 2.0 let session = URLSession(configuration: config) © akosma 2016 100
101. !" Excessive Curiosity © akosma 2016 101
102. Excessive User Interface Idiom Checks // Only if you need compatibility with iPhone OS 3.2... really? if UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiom.pad { // ... iPad-only code } let idiom = UIDevice.current().userInterfaceIdiom if idiom == UIUserInterfaceIdiom.phone { // ... iPhone-only code } © akosma 2016 102
103. Excessive OS Version Checks46 let ver = OperatingSystemVersion(majorVersion: 10, minorVersion: 0, patchVersion: 0) if ProcessInfo().isOperatingSystemAtLeast(ver) { ... } let os = ProcessInfo().operatingSystemVersion switch (os.majorVersion, os.minorVersion, os.patchVersion) { case (10, _, _): print("iOS >= 10.0.0") default: print("Previous versions") } 46 Source: NSHipster © akosma 2016 103
104. Behave Appropriately 1. Encapsulate features into subclasses 2. Last resort: check feature existence if let feature = NSClassFromString("INIntent") { print("Intents.framework (SiriKit) available") } © akosma 2016 104
105. © akosma 2016 105
106. ! Project Management Smells © akosma 2016 106
107. !" Invisible Documentation © akosma 2016 107
108. If you haven’t written documentation you haven’t done your job © akosma 2016 108
109. © akosma 2016 109
110. !" Folder Clusterfuck © akosma 2016 110
111. © akosma 2016 111
112. Extensions Explosion —19 iOS extensions —11 macOS extensions Check out Apple’s “Lister” application!99 99 Source: Apple Developer Library © akosma 2016 112
113. Conventions for Xcode28 —Create folders for each platform: iOS, macOS, watchOS, tvOS —Target folders inside platform folders —Shared folder for cross-platform files —Separate items into Assets and Source directories 28 Source: The.Swift.Dev © akosma 2016 113
114. !" Cocoapods Galore © akosma 2016 114
115. Cocoapods Best Practices —Check in Pods folder, Podfile and Podfile.lock. —pod outdated in a separate branch once a week —Use rbenv to control Ruby installations —Team uses the same version of Cocoapods © akosma 2016 115
116. Specify Pod Versions ✔ target 'MyApp' do pod 'AFNetworking', '~> 3.0' pod 'FBSDKCoreKit', '~> 4.9' end ➡ Choose your pods wisely! © akosma 2016 116
117. !" Rogue Compiler Warnings © akosma 2016 117
118. New in Xcode8 8 Source: WWDC 2016 Session 410 © akosma 2016 118
119. © akosma 2016 119
120. !" User Discrimination © akosma 2016 120
121. ♿"#$%& '()*+㊙ -./012 © akosma 2016 121
122. !" Interface Builder Attack © akosma 2016 122
123. © akosma 2016 123
124. Problem —Controllers tied to Storyboard ➡ hard to reuse —Merge conflicts —Slow loading —Complex navigation © akosma 2016 124
125. Solution —Use storyboards only for navigation —Use XIB files only for UI design Steps: 1. Menu Editor -> Refactor to Storyboard… 2. ViewController.swift + ViewController.xib 3. Remove view outlet from Storyboard in Controller © akosma 2016 125
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128. // Instantiating through the Storyboard if let controller = self.storyboard?.instantiateViewController(withIdentifier: "Ctrl") { // ... } // Instantiating manually // This constructor automatically loads XIB file let controller = ViewController() © akosma 2016 128
129. Learn more about Storyboards "Pro Storyboard Techniques" Tomorrow 16:10, by Joe Keeley, in the Main Hall © akosma 2016 129
130. !" iOS Nostalgia © akosma 2016 130
131. © akosma 2016 131
132. Formula for Happiness©™ Minimum iOS Version to Support = (Current iOS Version Number) – 1 ! © akosma 2016 132
133. !" Backend API Anarchy © akosma 2016 133
134. Common Backend API Sins —SOAP, XML-RPC —Chatty design —Lack of Control —QOS, Security, Performance… ! " ↩ # © akosma 2016 134
135. Repent Of Your Sins —Build your own API Proxy —Chunky design —Socket.io & GraphQL ☺ " 㲗 ‘ ↩ # © akosma 2016 135
136. © akosma 2016 136
137. Summary © akosma 2016 137
138. ! Swift and Cocoa Smells ! SwiftyLeaks " Hungarian Notation # Objective-C Nostalgia $ Homemade Cache % Tagged View & Illicit Association © akosma 2016 138
139. ! Class Design Smells ! Class Struggle " Massive View Controller & App Delegate # Forgotten Memory Warnings $ Long Switch Statement % Long Method Names & Excessive Curiosity © akosma 2016 139
140. ! Project Management Smells ! Invisible Documentation " Folder Clusterfuck # Cocoapods Galore $ Rogue Compiler Warnings % User Discrimination & Interface Builder Attack ' iOS Nostalgia ( Backend API Anarchy © akosma 2016 140
141. Got More Smells? Call to action! 1. Give smells a cool name and a description 2. Specify the refactoring 3. Share! © akosma 2016 141
142. ಧನ#$ದಗ'! ! धन्यवाद! ! Thanks! ! More information at about.me/akosma © akosma 2016 142
143. Questions? #AccessibleIndia © akosma 2016 143
144. © 2016 Adrian Kosmaczewskiakosma All Rights Reserved akosma https://twitter.com/akosma © akosma 2016 144