SwiftUI：绑定到@AppStorage

Posted 2023-03-17

【中文标题】SwiftUI：绑定到@AppStorage

【英文标题】：SwiftUI: Binding to @AppStorage

【发布时间】：2021-07-17 17:05:20

【问题描述】：

在以下示例中，如何根据 SwiftUI 更新 aArrived 和 bArrived 的方式更改 activeSheet 的值？

struct ContentView: View 

    @AppStorage("didAArrive") var aArrived: Bool = false
    @AppStorage("didBArrive") var bArrived: Bool = false

    enum ActiveSheet: Identifiable 
        case aArrived, bArrived

        var id: Int 
            hashValue
        
    

    @State private var activeSheet: ActiveSheet?

    var body: some View 
        Text("Hello")
            .sheet(
                item: $activeSheet,
                content:  item in
                    switch item 
                    case .aArrived:
                        Text("A arrived")
                    case .bArrived:
                        Text("B arrived")
                    
                
            )
    

【问题讨论】：

whatArrived 是否会独立于aArrived 或bArrived 而改变？如果不是，请不要将其设为 @State 变量，只需将其设为计算属性即可。

我需要它作为 sheet(item:) 修饰符的 item 参数，所以我认为我需要它是 State。

那只是意味着它需要是一个Binding。这将有助于根据要求更新问题。否则，听起来您已经知道如何使用 onAppear 和 onChange。

【参考方案1】：

您可以为根据aArrived 和bArrived 获取其值的工作表创建自定义绑定。绑定值将根据aArrived 或bArrived 进行初始化，并在每次任一更改时更新。

struct ContentView: View 

    @AppStorage("didAArrive") var aArrived: Bool = false
    @AppStorage("didBArrive") var bArrived: Bool = false

    enum ActiveSheet: Identifiable 
        case aArrived, bArrived

        var id: Int 
            hashValue
        
    

    var body: some View 
        let sheetBinding = Binding<ActiveSheet?>(
            get: 
                if aArrived && bArrived 
                    return ActiveSheet.aArrived
                 else if aArrived 
                    return ActiveSheet.aArrived
                 else if bArrived 
                    return ActiveSheet.bArrived
                 else 
                    return nil
                
            ,
            set:  _ in 
        )
        VStack(spacing: 20) 
            Toggle("A arrived", isOn: $aArrived)
            Toggle("B arrived", isOn: $bArrived)
        
        .sheet(
            item: sheetBinding,
            content:  item in
                switch item 
                case .aArrived:
                    Text("A arrived")
                case .bArrived:
                    Text("B arrived")
                
            
        )