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yhkaplan
January 21, 2020
Programming
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Property Wrappers
yhkaplan
January 21, 2020
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Transcript
Property Wrappers 1
What are they? 2
→ New in 5.1 → Java-like annotations → Can accept
(generic) parameters → Used in SwiftUI 3
Purpose 4
Examples 5
SwiftUI 6
struct ContentView: View { @State private var value = 0.0
var body: some View { VStack { Text("Value is \(value)") Slider(value: $value) } } } 7
UIKit/ Foundation 8
class ViewController: UIViewController { @Keychain(key: "secret_info") var secretInfo = ""
} 9
Let's make one! 10
@propertyWrapper struct TwelveOrLess { private var number = 0 var
wrappedValue: Int { get { return number } set { number = min(newValue, 12) } } } // Use struct S { @TwelveOrLess var num = 13 // 12 } 11
@propertyWrapper struct Clamped { private var number = 0 private
let maxNum: Int private let minNum: Int var wrappedValue: Int { get { return number } set { number = max(min(newValue, maxNum), minNum) } } } // Use struct S { @Clamped(maxNum: 10, minNum: 0) var num = 13 // 10 } 12
Projected values 13
@propertyWrapper struct State<T> { //... var projectedValue: Binding<T> } 14
struct ContentView: View { @State private var isDisabled = false
var body: some View { OtherView($isDisabled) // Binding<Bool> } } 15
Conclusion 16
More info 17
→ The Swift Programming Language → Burritos 18