Swift UI 细节删除

Question

我有一个 SwiftUI 列表，它在点击单元格时显示详细 View /推送到导航:

import SwiftUI

struct DevicesInRangeList: View {
    @ObservedObject var central = Central()

    var body: some View {
        NavigationView {
            List(central.peripheralsInRange) { peripheral in
                NavigationLink(destination: DeviceView(peripheral: peripheral).onAppear {
                    self.central.connect(peripheral: peripheral)
                }.onDisappear {
                    self.central.disconnect(peripheral: peripheral)
                }) {
                    DeviceRow(deviceID: peripheral.deviceID, name: peripheral.name)
                }
            }.onAppear {
                self.central.scanning = true
            }.onDisappear {
                self.central.scanning = false
            }.navigationBarTitle("Devices in range")
        }
    }
}

如果我点击一行，就会显示详细信息。如果外围设备断开连接，它会从 peripheralsInRange 数组中删除，并且该行会被删除——但仍会显示详细信息。删除关联行时如何删除详细信息？

---

编辑:在 Asperi 的回答之后，我得到了以下内容，但仍然不起作用:

struct DevicesInRangeList: View {
    @ObservedObject var central = Central()

    @State private var localPeripherals: [Peripheral] = []

    @State private var activeDetails = false
    var body: some View {
        NavigationView {
            List(localPeripherals, id: \.self) { peripheral in
                NavigationLink(destination:
                    DeviceView(peripheral: peripheral)
                        .onReceive(self.central.$peripheralsInRange) { peripherals in
                            if !peripherals.contains(peripheral) {
                                self.activeDetails = false
                            }
                        }
                        .onAppear {
                            self.central.connect(peripheral: peripheral)
                        }
                        .onDisappear {
                            self.central.disconnect(peripheral: peripheral)
                        }
                , isActive: self.$activeDetails) {
                    DeviceRow(deviceID: peripheral.deviceID, name: peripheral.name)
                }
            }.onReceive(central.$peripheralsInRange) { peripherals in
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                    self.localPeripherals = peripherals
                }
            }.onAppear {
                self.central.scanning = true
                self.localPeripherals = self.central.peripheralsInRange
            }.onDisappear {
                self.central.scanning = false
            }.navigationBarTitle("Devices in range")
        }
    }
}

Answer 1

最好的方法是在显示之前检查是否存在数据。我采用了apple的master/demo来展示如何做。在这个模板应用程序中，他们使用@State var 作为记录源，但想法是一样的。在详细 View 中检查是否存在“记录”。

import SwiftUI

private let dateFormatter: DateFormatter = {
    let dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .medium
    dateFormatter.timeStyle = .medium
    return dateFormatter
}()

struct ContentView: View {
    @State private var dates = [Date]()

    var body: some View {
        NavigationView {
            MasterView(dates: $dates)
                .navigationBarTitle(Text("Master"))
                .navigationBarItems(
                    leading: EditButton(),
                    trailing: Button(
                        action: {
                            withAnimation { self.dates.insert(Date(), at: 0) }
                        }
                    ) {
                        Image(systemName: "plus")
                    }
                )
            DetailView(dates: $dates).navigationBarTitle(Text("Detail"))
        }.navigationViewStyle(DoubleColumnNavigationViewStyle())
    }
}

struct MasterView: View {
    @Binding var dates: [Date]

    var body: some View {
        List {
            ForEach(dates, id: \.self) { date in
                NavigationLink(
                    destination: DetailView(dates: self._dates, selectedDate: date).navigationBarTitle(Text("Detail"))
                ) {
                    Text("\(date, formatter: dateFormatter)")
                }
            }.onDelete { indices in
                indices.forEach { self.dates.remove(at: $0) }
            }
        }
    }
}

struct DetailView: View {
    @Binding var dates: [Date]
    var selectedDate: Date?

    var body: some View {
            if let selectedDate = selectedDate, dates.contains(selectedDate) {
                return Text("\(selectedDate, formatter: dateFormatter)")
            } else {
                return Text("Detail view content goes here")
            }
    }
}


struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}