SwiftUI：@AppStorage 使用中的“属性初始化程序在 'self' 可用之前运行”

Question

我是 Swift 新手，想解决这个问题。我希望，当我关闭并返回应用程序时，选择器中的货币会被保存。 （通过@AppStorage）但是我不能使用我想到的任何东西在@AppStorage 中将$currency 定义为$cur。谢谢你的帮助！代码如下：

//Settings
struct SettingsView: View {

@State private var currency = "$"
var currencies = ["$", "€", "¥", "£"]
@AppStorage("name") var name = ""
@AppStorage("cur") var cur = "\($currency)"
//Cannot use instance member '$currency' within property initializer; property initializers run before 'self' is available

var body: some View {
    NavigationView {
        
        Form {
            Section(header: Text("Your name")) {
                TextField("Tim", text: $name)
            }
            
            Section(header: Text("Your currency")) {
                Picker(selection: $currency, label: Text("Your Currency")) {
                    ForEach(currencies, id: \.self) {
                        Text($0)
                    }
                }
                .pickerStyle(SegmentedPickerStyle())
            }
        }
        
    }
    .navigationTitle("Settings")
    }
}

Answer 1

定义cur 时不能引用$currency。这是 Swift 的一个限制。对您来说很明显货币已经具有价值，但 Swift 不会让您使用它，直到初始化程序完成设置 self.这与 AppStorage 无关——这是属性初始化器不能引用其他（非静态）属性的规则。

所以，这个

@State private var currency = "$"
@AppStorage("cur") var cur = "\($currency)"

可能

@State private var currency = "$"
@AppStorage("cur") var cur = "$" // set it to the same value

或

private static let dollar = "$"

@State private var currency = SettingsView.dollar
@AppStorage("cur") var cur = SettingsView.dollar