ITT 2016 - Michele Titolo - Cocoa Design Patterns in Swift

Michele Titolo talks about Cocoa Design Patterns in Swift. Swift has now been around for almost two years, and the language has evolved. What hasn't changed are the APIs in Apple's SDK you work with every day. As much as you want to embrace Swift, you still must understand the SDK conventions, many of which originated in the Cocoa era. Continuing to write Swift like Objective-C is not ideal or sustainable. Michele Titolo focuses on the existing patterns and how to make them more friendly in Swift.

Transcript

1. Cocoa Design Patterns
   in Swift @MicheleTitolo
3. Patterns
4. Protocols are first class citizens
5. Swift is a protocol-oriented language
6. AbsoluteValuable, AnyCollectionType, AnyObject, ArrayLiteralConvertible, BidirectionalIndexType, BitwiseOperationsType, BooleanLiteralConvertible, BooleanType, CVarArgType, CollectionType, Comparable, CustomDebugStringConvertible, CustomLeafReflectable, CustomPlaygroundQuickLookable, CustomReflectable, CustomStringConvertible, DictionaryLiteralConvertible, Equatable, ErrorType, ExtendedGraphemeClusterLiteralConvertible, FloatLiteralConvertible, FloatingPointType, ForwardIndexType, GeneratorType, Hashable, Indexable, IntegerArithmeticType, IntegerLiteralConvertible, IntegerType, IntervalType, LazyCollectionType, LazySequenceType, MirrorPathType, MutableCollectionType, MutableIndexable, MutableSliceable, NilLiteralConvertible, OptionSetType, OutputStreamType, RandomAccessIndexType, RangeReplaceableCollectionType, RawRepresentable, ReverseIndexType, SequenceType, SetAlgebraType, SignedIntegerType, SignedNumberType, Streamable, Strideable, StringInterpolationConvertible, StringLiteralConvertible, UnicodeCodecType, UnicodeScalarLiteralConvertible, UnsignedIntegerType @gregheo - Swift Summit SF 2015
7. Apple’s frameworks are protocol- oriented
8. Expect to use more protocols
9. Extensions
10. Like categories, but not
11. Provide default implementations
12. protocol Holder { typealias Item var items: [Item] { get set } } extension Holder { mutating func add(item: Item) { items.append(item) } }
13. Break up big classes
14. class MyTableViewController: UITableViewController { override func viewDidLoad() { super.viewDidLoad() if traitCollection.forceTouchCapability == .Available { registerForPreviewingWithDelegate(self, sourceView: tableView) } } } // MARK: Force Touch on Table Cell extension MyTableViewController: UIViewControllerPreviewingDelegate { … }
15. Composition > Hierarchy
16. Inheritance is limited
17. No type overriding
18. Use generics to workaround this
19. class Basket { var items = [AnyObject]() init(items: [AnyObject]) { self.items.appendContentsOf(items) } }
20. class Basket { var items = [AnyObject]() init(items: [AnyObject]) { self.items.appendContentsOf(items) } } class FruitBasket: Basket { init<T: AnyObject where T: Fruit>(items: [T]) { super.init(items: items) } }
22. let basket = FruitBasket(items: [Peach()])
24. Reference protocols, not implementors
25. View Controllers
26. Break up functionality
27. Reusable components
28. Generic components
29. Combine with other patterns such as MVVM
30. protocol FormRowViewModel { var title: String { get } var placeholder: String { get } func validationFunction() -> String -> Bool } class FormTableView<T: FormRowViewModel> UITableView { var rows = [T]() }
31. Why is this better than referencing the protocol?
32. class FormTableView: UITableView { var rows = [FormRowViewModel]() }
33. let table = FormTableView(frame: CGRectMake(0, 0, 100, 100), style: .Plain) let person = PeopleRowViewModel() table.rows.append(person) let bear = BearRowViewModel() table.rows.append(bear) !
34. let table = FormTableView<PeopleRowViewModel>(frame: CGRectMake(0, 0, 100, 100), style: .Plain) let person = PeopleRowViewModel() table.rows.append(person) let bear = BearRowViewModel() table.rows.append(bear)
35. Compose patterns
36. Property types
37. Lazy
38. Use values of object to set a property once
39. - (NSInteger)figureOutSomeState { if ([self.someOtherObject.someString isEqual:@"Hello"] && self.someFlag) { return 1; } else if (self.someOtherFlag && !self.someFlag) { return 2; } else if (self.someOtherFlag && self.someFlag && [self.someOtherObject.someString isEqual:@"Goodbye"]) { return 3; } return 0; }
40. lazy var someState: Int = { [unowned self] in if self.someOtherObject.title == "Hello" && self.someFlag { return 1 } else if self.someOtherFlag && !self.someFlag { return 2 } else if self.someOtherFlag && self.someFlag && self.someOtherObject.title == "Goodbye" { return 3 } return 0 }()
41. lazy var data: [SomeStruct] = { let initialStruct = SomeStruct() return [initialStruct] }()
42. Computed
43. No storage, just return value from calculation
44. var canLoadMore: Bool { get { if !loading && hasMoreToLoad { return true } return false } }
45. Computed properties cannot be KVO’d
46. Property observers
47. Observe properties on yourself
48. Better encapsulation Better organization
49. var refreshing = false { willSet(newRefreshing) { if (newRefreshing) { self.tableView.tableHeaderView = self.loadingView } else { self.tableView.tableHeaderView = nil } } }
50. Still need KVO
51. KVO only works on NSObjects
52. protocol Fruit: class, NSObject {}
53. Anti-Patterns
54. Operator overloading
55. Don’t overload default operators
56. Operators make code
    harder to read
57. func decode(json: JSON) -> User? { return _JSONObject(json) >>> { d in User.create <^> d["id"] >>> _JSONInt <*> d["name"] >>> _JSONString <*> d["email"] >>> _JSONString } }
58. Implicit Unwrapping
59. ❗
60. 0054 - Abolish ImplicitlyUnwrappedOptional type
61. Don’t overuse this
62. Type is important
63. Most common use case: set properties on a view controller
64. class MyTableViewController: UITableViewController { var dataSource: MyDataSourceProtocol! var viewModel: ItemListViewModel! }
65. In Summary
66. Beware being too Swift-y
67. Swift uses familiar patterns
68. Sometimes being Swift-y isn’t so different
69. Thanks! @MicheleTitolo
70. Photo Credits • https://www.flickr.com/photos/19779889@N00/26092186311/ • https://www.flickr.com/photos/55602651@N08/11338995214/ • https://www.flickr.com/photos/23813062@N08/6912401481/ • https://www.flickr.com/photos/92485952@N02/20167637213/ • https://www.flickr.com/photos/84047449@N00/21687886133 • https://www.flickr.com/photos/50318388@N00/2392118348 • https://www.flickr.com/photos/129231629@N05/20890434523/ • https://www.flickr.com/photos/39375632@N05/4604343140/ • https://www.flickr.com/photos/13696909@N00/23545354390/ • https://www.flickr.com/photos/132691994@N07/23756257432