如何附加到结构数组并保持更改？

Question

我希望能够将对象列表存储在单独的 Swift 文件中，并在页面中调用它们以显示它们。我用这段代码成功地做到了：

import Foundation
import SwiftUI



struct MatchInfo: Hashable, Codable {
    let theType: String
    let theWinner: String
    let theTime: String
    let id = UUID()
}


var matchInfo = [
MatchInfo(theType: "Capitalism", theWinner: "Julia", theTime: "3/3/2021"),
MatchInfo(theType: "Socialism", theWinner: "Julia", theTime: "3/2/2021"),
MatchInfo(theType: "Authoritarianism", theWinner: "Luke", theTime: "3/1/2021")
]

我在此处的另一个页面上播放比赛后附加到列表的位置：

 matchInfo.insert(MatchInfo(theType: typeSelection, theWinner: winnerName, theTime: "\(datetimeWithoutYear)" + "\(year)"), at: 0)

这是另一个页面上的一些代码，我将其称为列表：

List {
                    ForEach(matchInfo, id: \.self) { matchData in
                        
                        matchRow(matchData : matchData)
                        
                    } .background(Color("invisble"))
                    .listRowBackground(Color("invisble"))
                } .frame(height: 490)

...

struct matchRow: View {

let matchData: MatchInfo
 
var body: some View {
    HStack {
        VStack(alignment: .leading) {
            Text(matchData.theType)
                .font(.system(size: 20, weight: .medium, design: .default))
            Text("    Winner: " + matchData.theWinner)
        }
        Spacer()
    
        Text(matchData.theTime)
            .padding(.leading, 40)
            .multilineTextAlignment(.trailing)
    
    }
    .foregroundColor(.white)
    .accentColor(.white)
}
}

但此代码不会通过应用重新启动保存。我以前从未通过重新启动保存过任何东西，并且一直在努力寻找一个足够简单让我理解的答案。如何在下次打开应用时更新列表而不使其消失？

Answer 1

好的，这里有一个关于如何保存到文档文件夹/从文档文件夹加载的示例。

首先确保您的对象 MatchInfo 符合此协议。

import Foundation

protocol LocalFileStorable: Codable {
    static var fileName: String { get }
}

extension LocalFileStorable {
    static var localStorageURL: URL {
        guard let documentDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first else {
            fatalError("Can NOT access file in Documents.")
        }
        
        return documentDirectory
            .appendingPathComponent(self.fileName)
            .appendingPathExtension("json")
    }
}

extension LocalFileStorable {
    static func loadFromFile() -> [Self] {
        do {
            let fileWrapper = try FileWrapper(url: Self.localStorageURL, options: .immediate)
            guard let data = fileWrapper.regularFileContents else {
                throw NSError()
            }
            return try JSONDecoder().decode([Self].self, from: data)
            
        } catch _ {
            print("Could not load \(Self.self) the model uses an empty collection (NO DATA).")
            return []
        }
    }
}

extension LocalFileStorable {
    static func saveToFile(_ collection: [Self]) {
        do {
            let data = try JSONEncoder().encode(collection)
            let jsonFileWrapper = FileWrapper(regularFileWithContents: data)
            try jsonFileWrapper.write(to: self.localStorageURL, options: .atomic, originalContentsURL: nil)
        } catch _ {
            print("Could not save \(Self.self)s to file named: \(self.localStorageURL.description)")
        }
    }
}

extension Array where Element: LocalFileStorable {
    ///Saves an array of LocalFileStorables to a file in Documents
    func saveToFile() {
        Element.saveToFile(self)
    }
}

您的主内容视图应如下所示：（我修改了您的对象以使其更简单。）

import SwiftUI

struct MatchInfo: Hashable, Codable, LocalFileStorable {
    static var fileName: String {
        return "MatchInfo"
    }
    
    let description: String
}

struct ContentView: View {
    @State var matchInfos = [MatchInfo]()
    
    var body: some View {
        VStack {
            Button("Add Match Info:") {
                matchInfos.append(MatchInfo(description: "Nr." + matchInfos.count.description))
                MatchInfo.saveToFile(matchInfos)
            }
            List(matchInfos, id: \.self) {
                Text($0.description)
            }
            .onAppear(perform: {
                matchInfos = MatchInfo.loadFromFile()
            })
        }
    }
}