arrays - How to Store Nested Arrays in @AppStorage for SwiftUI

Question

@AppStorage was introduced in SwiftUI recently, it seems like an alternative to UserDefaults. I'm trying to make the @AppStorage able to store nested lists.

For simple cases, you would do

@AppStorage("selected") var selected = 0

I used this while dealing with normal UserDefaults:

@Published var list = UserDefaults.standard.array(forKey: "nestedList") as? [[String]] ?? [[String]]()

Long story short, how do I convert plain old UserDefuaults to the new property wrapper, @AppStorage?

标签： arraysswiftswiftuinsuserdefaultsswiftui-list

Answer 1

All you need is to conform Array to RawRepresentable using the extension from here:

extension Array: RawRepresentable where Element: Codable {
    public init?(rawValue: String) {
        guard let data = rawValue.data(using: .utf8),
              let result = try? JSONDecoder().decode([Element].self, from: data)
        else {
            return nil
        }
        self = result
    }

    public var rawValue: String {
        guard let data = try? JSONEncoder().encode(self),
              let result = String(data: data, encoding: .utf8)
        else {
            return "[]"
        }
        return result
    }
}

Here is a demo:

struct ContentView: View {
    @AppStorage("items") var items: [[String]] = [
        ["1", "2"],
        ["a", "b", "c"],
    ]

    var body: some View {
        VStack {
            Text("items: \(String(describing: items))")
            Button("Add item") {
                items[0].append(String(Int.random(in: 1...10)))
            }
        }
    }
}