不能在属性初始值设定项中使用实例成员“dateType”；属性初始化程序在“self”可用之前运行[重复]

Question

我对 SwiftUI 很陌生，无法绕过这个错误。 我正在尝试在同一个初始化程序中的另一个数组中使用两个 @State 变量（isGlobal 和 dataType）。

我不断收到错误消息： “不能在属性初始值设定项中使用实例成员 'dateType'；属性初始值设定项在 'self' 可用之前运行”和 "不能在属性初始化器中使用实例成员 'isGlobal'；属性初始化器在 'self' 可用之前运行"

这是视图开头的代码：

struct Home : View {
@State var dateType : Int
@State var isGlobal = true

@State var dailyVax = [
    
    DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 6))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 6))", show: true),
    DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 5))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 5))", show: false),
    DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 4))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 4))", show: false),
    DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 3))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 3))", show: false),
    DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 2))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 2))", show: false),
    DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 1))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 1))", show: false),
    DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 0))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 0))", show: false),
]

var body: some View { ...

这是 [DailyVaccinations] 结构：

struct DailyVaccinations : Identifiable {
var id = UUID().uuidString
var day : String
var value : String
var show : Bool

}

下面是实际使用“dailyVax”数组的代码：

ForEach(dailyVax.indices,id: \.self){i in
                        
                        
                        GraphView(data: dailyVax[i], allData: dailyVax)
                            .onTapGesture {
                            
                                withAnimation{
                                    
                                    for index in 0..<dailyVax.count{
                                        dailyVax[index].show = false
                                    }
                                    dailyVax[i].show.toggle()
                                }
                                
                            }
                        
                        if dailyVax[i].value != dailyVax.last!.value {
                            Spacer(minLength: 0)
                        }
                        
                    } ...

如果有人能帮我解决这个问题，将不胜感激！谢谢你

Answer 1

您收到此错误消息是因为您尝试在初始化程序中访问 isGlobal 和 dateType。

当尚未定义所有值时，您无法执行此操作，因此错误消息中的“before self is available”。

要解决此问题，请编写自定义初始化程序：

init(dateType: Int, isGlobal: Bool = true) {
        self.dateType = dateType
        self.isGlobal = isGlobal
        
        self.dailyVax = [
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 6))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 6))", show: true),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 5))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 5))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 4))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 4))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 3))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 3))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 2))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 2))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 1))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 1))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 0))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 0))", show: false)
        ]
        
// Note that all values are being given a value in the initializer (dateType, isGlobal, and dailyVax)


    }

通过这样做，SwiftUI 知道所有值都在更改和/或使用初始化程序中提供的任何其他值之前被初始化。我对 SwiftUI 也很陌生，但这是我对它的理解。有关初始化程序如何工作以及它们可以做什么的更多信息，我建议在 Google 上搜索有关该主题的更多信息和/或访问官方 Swift 文档：

https://docs.swift.org/swift-book/LanguageGuide/Initialization.html

这就是你的代码最终的样子：

struct Home : View {
    @State var dateType: Int
    @State var isGlobal: Bool
    
    @State var dailyVax: [DailyVaccinations]
    
    init(dateType: Int, isGlobal: Bool = true) {
        self.dateType = dateType
        self.isGlobal = isGlobal
        
        self.dailyVax = [
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 6))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 6))", show: true),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 5))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 5))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 4))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 4))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 3))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 3))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 2))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 2))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 1))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 1))", show: false),
            DailyVaccinations(day: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: false, dayCt: 0))", value: "\(showData(tabType: isGlobal, date: dateType, dataType: 4, change: true, dayCt: 0))", show: false)
        ]

    }
    
    var body: some View {
        ...
    }
    
}