Question

我有一个存储在 CoreData 中的项目列表和一个右上角的添加按钮，用于将项目添加到列表并以编程方式导航到 ItemView。当列表中没有项目并且我按下添加按钮时，创建的项目会按预期滑入，但 NavigationLink 不会自动导航到其 ItemView。此外，NavigationLink 在点击它时甚至不起作用。

仅当再次按下添加按钮时（在第二项中滑动），NavigationLinks 才会按预期开始工作。

重现步骤：

创建一个新的单一视图应用程序，然后单击 CoreData 并在 CloudKit 中托管。应该已经在 CoreData 中存储了一个 Item Entity。
用这个替换 ContentView.swift：

import SwiftUI
import CoreData

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext

    @State private var selection: Date?

    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Item.timestamp, ascending: true)],
        animation: .default)
    private var items: FetchedResults<Item>

    var body: some View {
        NavigationView {
            List {
                ForEach(items) { item in
                    NavigationLink(
                        "Item at \(item.timestamp!, formatter: itemFormatter)",
                        destination: ItemView(item: item),
                        tag: item.timestamp!,
                        selection: $selection
                    )
                }
                .onDelete(perform: deleteItems)
            }
            .listStyle(InsetGroupedListStyle())
            .navigationTitle("Items")
            .toolbar {
                Button(action: addItem) {
                    Label("Add Item", systemImage: "plus")
                }
            }
        }
    }

    private func addItem() {
        withAnimation {
            let newItem = Item(context: viewContext)
            newItem.timestamp = Date()

            do {
                try viewContext.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nsError = error as NSError
                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
            }
            selection = newItem.timestamp
        }
    }

    private func deleteItems(offsets: IndexSet) {
        withAnimation {
            offsets.map { items[$0] }.forEach(viewContext.delete)

            do {
                try viewContext.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nsError = error as NSError
                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
            }
        }
    }
}

struct ItemView: View {

    let item: Item

    var body: some View {
        Text("Item at \(item.timestamp!, formatter: itemFormatter)")
    }
}

private let itemFormatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateStyle = .short
    formatter.timeStyle = .medium
    return formatter
}()

点击右上角的添加按钮。然后尝试单击 NavigationLink。它不会导航。只有再次按下添加按钮时，它才会按预期工作。

Answer 1

我在 0.5 秒后异步更新选择，错误消失了。不确定这是否是一个可靠的解决方案，但从用户的角度来看，首先看到项目滑入并在之后导航是很直观的。

DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
     selection = newItem.timestamp
}

CoreData 的程序化导航奇怪行为

1 个答案: