下面是我制作的一个工作示例，它扩展了默认的 Core Data SwiftUI 应用程序模板，以在工作表中添加项目时间戳的编辑。该工作表在子上下文中加载该项目，以便可以进行编辑，如果取消，编辑将被丢弃，但如果保存，则更改将被推送到视图上下文中并保存。如果您不熟悉用于编辑的子上下文，我推荐 Apple 的旧版本CoreDataBooks 示例项目 https://developer.apple.com/library/archive/samplecode/CoreDataBooks/Introduction/Intro.html#//apple_ref/doc/uid/DTS40008405.
您需要知道的主要事情是，当我们使用工作表来编辑某些内容时，我们使用的版本采用的是项目而不是布尔值。这允许您正确配置编辑视图。
import SwiftUI
import CoreData
struct ItemEditorConfig: Identifiable {
let id = UUID()
let context: NSManagedObjectContext
let item: Item
init(viewContext: NSManagedObjectContext, objectID: NSManagedObjectID) {
// create the scratch pad context
context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
context.parent = viewContext
// load the item into the scratch pad
item = context.object(with: objectID) as! Item
}
}
struct ItemEditor: View {
@ObservedObject var item: Item // this is the scratch pad item
@Environment(\.managedObjectContext) private var context
@Environment(\.dismiss) private var dismiss
let onSave: () -> Void
@State var errorMessage: String?
var body: some View {
NavigationView {
Form {
Text(item.timestamp!, formatter: itemFormatter)
if let errorMessage = errorMessage {
Text(errorMessage)
}
Button("Update Time") {
item.timestamp = Date()
}
}
.toolbar {
ToolbarItem(placement: .navigationBarLeading) {
Button("Cancel") {
dismiss()
}
}
ToolbarItem(placement: .navigationBarTrailing) {
Button("Save") {
// first save the scratch pad context then call the handler which will save the view context.
do {
try context.save()
errorMessage = nil
onSave()
} catch {
let nsError = error as NSError
errorMessage = "Unresolved error \(nsError), \(nsError.userInfo)"
}
}
}
}
}
}
}
struct DetailView: View {
@Environment(\.managedObjectContext) private var viewContext
@ObservedObject var item: Item
@State var itemEditorConfig: ItemEditorConfig?
var body: some View {
Text("Item at \(item.timestamp!, formatter: itemFormatter)")
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
Button(action: edit) {
Text("Edit")
}
}
}
.sheet(item: $itemEditorConfig, onDismiss: didDismiss) { config in
ItemEditor(item: config.item) {
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)")
}
itemEditorConfig = nil
}
.environment(\.managedObjectContext, si.context)
}
}
func edit() {
itemEditorConfig = ItemEditorConfig(viewContext: viewContext, objectID: item.objectID)
}
func didDismiss() {
// Handle the dismissing action.
}
}
struct ContentView: View {
@Environment(\.managedObjectContext) private var viewContext
@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 {
DetailView(item: item)
} label: {
Text(item.timestamp!, formatter: itemFormatter)
}
}
.onDelete(perform: deleteItems)
}
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
EditButton()
}
ToolbarItem {
Button(action: addItem) {
Label("Add Item", systemImage: "plus")
}
}
}
Text("Select an item")
}
}
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)")
}
}
}
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)")
}
}
}
}
private let itemFormatter: DateFormatter = {
let formatter = DateFormatter()
formatter.dateStyle = .short
formatter.timeStyle = .medium
return formatter
}()
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView().environment(\.managedObjectContext, PersistenceController.preview.container.viewContext)
}
}
