SwiftUIで勘違いした話

最近、本格的にSwiftUIを触り始めたところ、この前、盛大に勘違いしてやらかしてしまいました。その経緯と関連するトピックがおもしろかったので紹介します。

どこで勘違いしてしまったか考えながら見てみて下さい。

1. Swi$ UIͰצҧ͍ͨ͠࿩ Yuta Koshizawa @koher
2. @koher • try! Swi* Tokyo • 2016, 2018 • iOSDC Japan • 2017, 2018, 2019 • Qiita • "Swi*ͷOp?onalܕΛۃΊΔ" • "JavaϓϩάϥϚͷͨΊͷKotlinೖ໳" • ...
3. Swi$ UIͰצҧ͍ͨ͠࿩ ! ๻͕Ͳ͜Ͱצҧ͍͔ͨ͠ ߟ͑ͳ͕Βฉ͍ͯΈͯԼ͍͞
9. struct CounterView: View { @State var count: Int = 0 var body: some View { VStack { Text("\(count)") .font(.largeTitle) Stepper("count", value: $count) .labelsHidden() } } }
10. struct CounterView: View { @State var count: Int = 0 var body: some View { VStack { Text("\(count)") .font(.largeTitle) Stepper("count", value: $count) .labelsHidden() } } }
11. SE-0258: Property Wrappers1 Status: Implemented (Swi. 5.1) • @State • @ObservedObject • @Binding • @Published • ... 1 h$ps:/ /github.com/apple/swi6-evolu9on/blob/master/proposals/0258-property-wrappers.md
12. projectedValue2 $count Property Wrapper projectedValue @State Binding<Value> @Binding Binding<Value> @Published Published<Value>.Publisher 2 h$ps:/ /docs.swi/.org/swi/-book/LanguageGuide/Proper<es.html#ID619
13. struct CounterView: View { @State var count: Int = 0 var body: some View { VStack { Text("\(count)") .font(.largeTitle) Stepper("count", value: $count) .labelsHidden() } } }
14. struct CounterView: View { @State var count: Int = 0 var body: some View { VStack { Text("\(count)") .font(.largeTitle) Stepper("count", value: $count) .labelsHidden() } } }
15. struct CounterView: View { @State var count: Int = 0 var body: some View { VStack { Text("\(count)") .font(.largeTitle) Stepper("count", value: $count) .labelsHidden() } } }
16. import Combine final class Counter: ObservableObject { @Published var count: Int = 0 }
17. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { Text("\(counter.count)") .font(.largeTitle) Stepper("count", value: $counter.count) .labelsHidden() } } }
18. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { Text("\(counter.count)") .font(.largeTitle) Stepper("count", value: $counter.count) .labelsHidden() } } }
19. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { Text("\(counter.count)") .font(.largeTitle) Stepper("count", value: $counter.count) .labelsHidden() } } }
21. struct NumberDisplay: View { @Binding var number: Int var body: some View { return HStack { ForEach(digits(from: number)) { Image(systemName:"\($0.value).circle.fill") .resizable() .frame(width: 64, height: 64) } } } ... }
22. struct NumberDisplay: View { @Binding var number: Int var body: some View { return HStack { ForEach(digits(from: number)) { Image(systemName:"\($0.value).circle.fill") .resizable() .frame(width: 64, height: 64) } } } ... }
23. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.count) Stepper("count", value: $counter.count) .labelsHidden() } } }
24. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.count) Stepper("count", value: $counter.count) .labelsHidden() } } }
25. import Combine final class Counter: ObservableObject { @Published var count: Int = 0 }
26. import Combine final class Counter: ObservableObject { @Published private(set) var count: Int = 0 func increment() { count += 1 } func reset() { count = 0 } }
31. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.count) // HStack { Button("Reset") { self.counter.reset() } Button("Increment") { self.counter.increment() } } } } }
32. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.count) // HStack { Button("Reset") { self.counter.reset() } Button("Increment") { self.counter.increment() } } } } }
33. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.count) // HStack { Button("Reset") { self.counter.reset() } Button("Increment") { self.counter.increment() } } } } }
34. $counter.count ͳΜͰ Counter ͷϓϩύςΟʹ ΞΫηεͰ͖Δͷʁ
35. ObservedObject.projectedValue3 var projectedValue: ObservedObject<ObjectType>.Wrapper 3 h$ps:/ /developer.apple.com/documenta6on/swi9ui/observedobject/projectedvalue
36. ObservedObject.Wrapper .subscript(dynamicMember:)4 subscript<Subject>( dynamicMember keyPath: ReferenceWritableKeyPath<ObjectType, Subject> ) -> Binding<Subject> 4 h$ps:/ /developer.apple.com/documenta6on/swi9ui/observedobject/wrapper/subscript(dynamicmember:)
37. ObservedObject.Wrapper .subscript(dynamicMember:)4 subscript<Subject>( dynamicMember keyPath: ReferenceWritableKeyPath<ObjectType, Subject> ) -> Binding<Subject> 4 h$ps:/ /developer.apple.com/documenta6on/swi9ui/observedobject/wrapper/subscript(dynamicmember:)
38. SE-0195: Introduce User-defined "Dynamic Member Lookup" Types 5 Status: Implemented (Swi. 4.2) @dynamicMemberLookup enum JSON { ... subscript(dynamicMember member: String) -> JSON? { ... } } 5 h$ps:/ /github.com/apple/swi6-evolu9on/blob/master/proposals/0195-dynamic-member-lookup.md
39. SE-0252: Key Path Member Lookup6 Status: Implemented (Swi. 5.1) @dynamicMemberLookup struct Lens<T> { ... subscript<U>(dynamicMember keyPath: WritableKeyPath<T, U>) -> Lens<U> { ... } } 6 h$ps:/ /github.com/apple/swi6-evolu9on/blob/master/proposals/0252-keypath-dynamic-member-lookup.md
40. ObservedObject.Wrapper subscript<Subject>( dynamicMember keyPath: ReferenceWritableKeyPath<ObjectType, Subject> ) -> Binding<Subject>
41. ObservedObject.Wrapper subscript<Subject>( dynamicMember keyPath: ReferenceWritableKeyPath<ObjectType, Subject> ) -> Binding<Subject>
42. ૒ํ޲όΠϯσΟϯά ( Stepper ) ↓ Ұํ޲όΠϯσΟϯά ( NumberDisplay )
43. ObservedObject.Wrapper subscript<Subject>( dynamicMember keyPath: ReferenceWritableKeyPath<ObjectType, Subject> ) -> Binding<Subject>
44. ReadOnly subscript<Subject>( dynamicMember keyPath: KeyPath<ObjectType, Subject> ) -> Binding<Subject>
45. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.count) // HStack { Button("Reset") { self.counter.reset() } Button("Increment") { self.counter.increment() } } } } }
46. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.readOnly // .count) HStack { Button("Reset") { self.counter.reset() } Button("Increment") { self.counter.increment() } } } } }
47. ObservedObject.Wrapper.ReadOnly extension ObservedObject.Wrapper { var readOnly: ReadOnly { return ReadOnly(unsafeBitCast(self, to: ObjectType.self)) // } @dynamicMemberLookup struct ReadOnly { private let object: ObjectType init(_ object: ObjectType) { self.object = object } subscript<Subject>(dynamicMember keyPath: KeyPath<ObjectType, Subject>) -> Binding<Subject> { Binding<Subject>( get: { self.object[keyPath: keyPath] }, set: { _ in assertionFailure("Read-only") } ) } } }
48. One-way data binding from @ObservedObject with Swi9UI7 Is it possible to achieve one-way data binding with Swi6UI in situa9ons like below? import Combine final class Counter: ObservableObject { @Published private(set) var count: Int = 0 func increment() { count += 1 } func reset() { count = 0 } } ... 7 h$ps:/ /forums.swi1.org/t/one-way-data-binding-from-observedobject-with-swi1ui/37547
49. struct NumberDisplay: View { @Binding var number: Int var body: some View { return HStack { ForEach(digits(from: number)) { Image(systemName:"\($0.value).circle.fill") .resizable() .frame(width: 64, height: 64) } } } ... }
50. struct NumberDisplay: View { let number: Int var body: some View { return HStack { ForEach(digits(from: number)) { Image(systemName:"\($0.value).circle.fill") .resizable() .frame(width: 64, height: 64) } } } ... }
51. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: $counter.readOnly .count) HStack { Button("Reset") { self.counter.reset() } Button("Increment") { self.counter.increment() } } } } }
52. struct CounterView: View { @ObservedObject var counter: Counter var body: some View { VStack { NumberDisplay(number: counter.count) HStack { Button("Reset") { self.counter.reset() } Button("Increment") { self.counter.increment() } } } } }
53. όΠϯσΟϯά͠ͳ͍ͱ มߋ͕൓ө͞Εͳ͘ͳ͍ʁ
54. Swi$UI ͷ View ͸ Ծ૝ View ͳͷͰ͜ΕͰ OK
55. Swi$UI ͷجૅதͷجૅ
56. ͳΜͰצҧ͍ͨ͠ʁ • Ծ૝ View ͷߟ͑ํΛཧղͯ͠Δͭ΋Γ͚ͩͬͨͲ׳Ε͕଍Γ ͳ͔ͬͨ • ૒ํ޲όΠϯσΟϯά → Ұํ޲όΠϯσΟϯά ͷॱʹߟ͑ͨ • Swi)UI ͸·ͩ·ͩػೳ͕଍Γͳ͍ͱ͍͏ઌೖ؍͕͋ͬͨ
57. ஏ͔͍ͣ͠ࢥ͍Λ͚ͨ͠ΕͲ΋ 3 ෼Ͱ໰୊͕ղܾͨ͠
58. Θ͔Βͳ͍͜ͱΛஏ͔͕ͣ͠Βͣ ࣭໰͢Δ͜ͱ͸େࣄ
59. Ͱ΋ɺ΍ͬͺΓஏ͔͍ͣ͠
60. Swi$ Zoomin' #3 ಗ໊࣭໰ձ ໌೔ 21:00- h"ps:/ /swi)-tweets.connpass.com/event/176665/