SwiftUI：如何在另一个视图中更新传递的数组项

Question

我正在尝试使用在 Textfield 中键入的新值更新数组项，但未使用编辑值更新列表。

我的代码是：

型号：

    struct WalletItem: Identifiable{

        let id = UUID()
        var name:String
        var cardNumber:String
        var type:String
        var cvc:String
        let pin:String
        var dateOfExpiry:String
    }

模型视图：

    class Wallet: ObservableObject{

        @Published var wallets = [
            WalletItem(name: "BSB", cardNumber: "123456789", type: "master card", cvc: "1234", pin: "1234", dateOfExpiry: "2016-06-29"),
            WalletItem(name: "Alpha bank", cardNumber: "123456789", type: "master card", cvc: "1234", pin: "1234", dateOfExpiry: "2017-03-12"),
            WalletItem(name: "MTБ", cardNumber: "123456789", type: "master card", cvc: "1234", pin: "1234", dateOfExpiry: "2020-11-12"),
        ]

    }

第一次查看：

    struct WalletListView: View {

        // Properties
        // ==========

        @ObservedObject var wallet = Wallet()
        @State var isNewItemSheetIsVisible = false


        var body: some View {
            NavigationView {
                List(wallet.wallets) { walletItem in
                    NavigationLink(destination: EditWalletItem(walletItem: walletItem)){
                            Text(walletItem.name)
                        }
                }
                .navigationBarTitle("Cards", displayMode: .inline)
                .navigationBarItems(
                    leading: Button(action: { self.isNewItemSheetIsVisible = true
                    }) {
                        HStack {
                            Image(systemName: "plus.circle.fill")
                            Text("Add item")
                        }
                    }
                )
            }
            .sheet(isPresented: $isNewItemSheetIsVisible) {
                NewWalletItem(wallet: self.wallet)
            }
        } 

    }

和次要观点：

    struct EditWalletItem: View {

        @State var walletItem: WalletItem


        @Environment(\.presentationMode) var presentationMode

        var body: some View {
            Form{
                Section(header: Text("Card Name")){
                    TextField("", text: $walletItem.name)
                }

            }
            .navigationBarItems(leading:
                Button(action: {
                    self.presentationMode.wrappedValue.dismiss()
                })
                {
                    Text("Back")
                }, trailing:
                Button(action: {

                    self.presentationMode.wrappedValue.dismiss()
                })
                {
                    Text("Save")
            })

        }

    }

P.S：如果我使用@Binding 而不是@State，我在第一个视图中会出现错误：初始化程序init(_:) 要求Binding<String> 符合StringProtocol

Answer 1

这里是修改过的部分（测试并适用于 Xcode 11.2 / iOS 13.2）：

1) 确定过度绑定

struct EditWalletItem: View {
    @Binding var walletItem: WalletItem

2) 传递地点

List(Array(wallet.wallets.enumerated()), id: \.element.id) { (i, walletItem) in
    NavigationLink(destination: EditWalletItem(walletItem: self.$wallet.wallets[i])){
            Text(walletItem.name)
        }
}

Answer 2

ForEach(Array(list.enumerated())) 只有在列表是 Array 而不是 ArraySlice 时才能正常工作，并且它具有复制列表的缺点。

更好的方法是使用.indexed() 助手：

struct IndexedCollection<Base: RandomAccessCollection>: RandomAccessCollection {
    typealias Index = Base.Index
    typealias Element = (index: Index, element: Base.Element)
    let base: Base
    var startIndex: Index { self.base.startIndex }
    var endIndex: Index { self.base.endIndex }

    func index(after i: Index) -> Index {
        self.base.index(after: i)
    }

    func index(before i: Index) -> Index {
        self.base.index(before: i)
    }

    func index(_ i: Index, offsetBy distance: Int) -> Index {
        self.base.index(i, offsetBy: distance)
    }

    subscript(position: Index) -> Element {
        (index: position, element: self.base[position])
    }
}

extension RandomAccessCollection {
    func indexed() -> IndexedCollection<Self> {
        IndexedCollection(base: self)
    }
}

例子：

// SwiftUIPlayground
// https://github.com/ralfebert/SwiftUIPlayground/

import Foundation
import SwiftUI

struct Position {
    var id = UUID()
    var count: Int
    var name: String
}

class BookingModel: ObservableObject {

    @Published var positions: [Position]

    init(positions: [Position] = []) {
        self.positions = positions
    }

}

struct EditableListExample: View {

    @ObservedObject var bookingModel = BookingModel(
        positions: [
            Position(count: 1, name: "Candy"),
            Position(count: 0, name: "Bread"),
        ]
    )

    var body: some View {
        // >>> Passing a binding into an Array via index:
        List(bookingModel.positions.indexed(), id: \.element.id) { i, _ in
            PositionRowView(position: self.$bookingModel.positions[i])
        }
    }
}

struct PositionRowView: View {

    @Binding var position: Position

    var body: some View {
        Stepper(
            value: $position.count,
            label: {
                Text("\(position.count)x \(position.name)")
            }
        )
    }

}

struct EditableListExample_Previews: PreviewProvider {
    static var previews: some View {
        EditableListExample()
    }
}

另见：

• How does the Apple-suggested .indexed() property work in a ForEach?