SwiftUI WatchKit列表在使用onDelete和确认提示框时无法正确更新表格视图。

Question

有人能指点我如何实现一个带有确认删除功能的简单列表，或者至少展示最佳实践。

如果删除部分是立即进行的并且去掉警告部分，下面的代码将起作用。不知何故，确认警告的呈现会使删除操作在错误的人员列表上进行。第一次删除还会给出控制台警告：

[TableView] Warning once only: UITableView was told to layout its visible cells and other contents without being in the view hierarchy (the table view or one of its superviews has not been added to a window). This may cause bugs by forcing views inside the table view to load and perform layout without accurate information (e.g. table view bounds, trait collection, layout margins, safe area insets, etc), and will also cause unnecessary performance overhead due to extra layout passes. Make a symbolic breakpoint at UITableViewAlertForLayoutOutsideViewHierarchy to catch this in the debugger and see what caused this to occur, so you can avoid this action altogether if possible, or defer it until the table view has been added to a window.

然而，我不知道如何解决这个问题，除非去掉警告。顺便说一句，在我的Mac更新Xcode之前的几周，这段精确的代码是可以工作的。

import Foundation
import SwiftUI
import Combine

struct Person: Identifiable{
    var id: Int
    var name: String

    init(id: Int, name: String){
        self.id = id
        self.name = name
    }

}

class People: ObservableObject{
    @Published var people: [Person]


    init(){
        self.people = [
            Person(id: 1, name:"One"),
            Person(id: 2, name:"Two"),
            Person(id: 3, name:"Three"),
            Person(id: 4, name:"Four")]
    }

}

struct ContentView: View {
    @ObservedObject var mypeople: People = People()
    @State private var showConfirm = false
    @State private var idx = 0

    func setDeletIndex(at idxs:IndexSet) {
        self.showConfirm = true
        self.idx = idxs.first!
    }
    func delete() {
        self.mypeople.people.remove(at: idx)
    }
    var body: some View {
        VStack {
            List {

                Text("Currently \(mypeople.people.count) persons").font(.footnote)
                    .alert(isPresented: $showConfirm) {
                        Alert(title: Text("Delete"), message: Text("Sure?"),
                              primaryButton: .cancel(),
                              secondaryButton: .destructive(Text("Delete")) {

                                self.delete()
                            })
                }

                ForEach(mypeople.people){ person in
                    Text("\(person.name)")
                }.onDelete { self.setDeletIndex(at: $0) }
            }
        }
    }
}


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

- Joakim Poromaa Helger

Answer 1

问题是由于更新警报关闭和清单记录删除之间的冲突。有效的解决方法是延迟删除，如下所示（在 Xcode 11.4 中测试）。

Text("Currently \(mypeople.people.count) persons").font(.footnote)
    .alert(isPresented: $showConfirm) {
        Alert(title: Text("Delete"), message: Text("Sure?"),
              primaryButton: .cancel(),
              secondaryButton: .destructive(Text("Delete")) {
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) { // here !!
                    self.delete()
                }
            })
}

- Asperi

---

谢谢！这是一个当前的bug还是苹果有其他更优选的解决方案？我的意思是，这不可能是第一次有人想要类似的功能吧？ - Joakim Poromaa Helger

您可以向苹果提交反馈。 - Asperi