Property Wrappers

Transcript

1. Property Wrappers 1
2. What are they? 2
3. → New in 5.1 → Java-like annotations → Can accept (generic) parameters → Used in SwiftUI 3
4. Purpose 4
5. Examples 5
6. SwiftUI 6
7. struct ContentView: View { @State private var value = 0.0 var body: some View { VStack { Text("Value is \(value)") Slider(value: $value) } } } 7
8. UIKit/ Foundation 8
9. class ViewController: UIViewController { @Keychain(key: "secret_info") var secretInfo = "" } 9
10. Let's make one! 10
11. @propertyWrapper struct TwelveOrLess { private var number = 0 var wrappedValue: Int { get { return number } set { number = min(newValue, 12) } } } // Use struct S { @TwelveOrLess var num = 13 // 12 } 11
12. @propertyWrapper struct Clamped { private var number = 0 private let maxNum: Int private let minNum: Int var wrappedValue: Int { get { return number } set { number = max(min(newValue, maxNum), minNum) } } } // Use struct S { @Clamped(maxNum: 10, minNum: 0) var num = 13 // 10 } 12
13. Projected values 13
14. @propertyWrapper struct State<T> { //... var projectedValue: Binding<T> } 14
15. struct ContentView: View { @State private var isDisabled = false var body: some View { OtherView($isDisabled) // Binding<Bool> } } 15
16. Conclusion 16
17. More info 17
18. → The Swift Programming Language → Burritos 18