我有一个最小的示例项目CD传递Q https://github.com/ericg-xcode-questions/CDPassingQ
我的主要（内容视图 https://github.com/ericg-xcode-questions/CDPassingQ/blob/main/CDPassingQ/ContentView.swift） 好像：
import SwiftUI
import CoreData
struct ContentView: View {
@Environment( \.managedObjectContext ) private var viewContext
@FetchRequest( sortDescriptors: [ NSSortDescriptor( keyPath: \Item.name, ascending: true ) ],
animation: .default )
private var items: FetchedResults<Item>
var body: some View {
NavigationView {
List {
ForEach( items ) { item in
NavigationLink {
NameViewer( itemID: item.objectID )
} label: {
Text( item.name! )
}
}
.onDelete( perform: deleteItems )
}
.toolbar {
ToolbarItem( placement: .navigationBarTrailing ) {
EditButton()
}
ToolbarItem {
Button() {
print( "Add Item" )
} label: {
NavigationLink {
NameViewer();
} label: {
Label( "Add Item", systemImage: "plus" )
}
}
}
}
}
}
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 ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView().environment(\.managedObjectContext, PersistenceController.preview.container.viewContext)
}
}
and 名称查看器 https://github.com/ericg-xcode-questions/CDPassingQ/blob/main/CDPassingQ/NameViewer.swift好像：
import SwiftUI
import CoreData
enum TrustReason: String, Identifiable, CaseIterable
{
var id: UUID
{
return UUID();
}
case unknown = "Unknown";
case legalOnly = "Legal Only";
case goodLabeling = "Good Labeling";
case facilityClean = "Facility Clean";
case detailedAnswers = "Detailed Answers";
case unresponsive = "Unresponsive";
}
extension TrustReason
{
var title: String
{
switch self
{
case .unknown:
return "Unknown";
case .legalOnly:
return "Legal Only";
case .goodLabeling:
return "Good Labeling";
case .facilityClean:
return "Facility Clean";
case .detailedAnswers:
return "Detailed Answers";
case .unresponsive:
return "Unresponsive";
}
}
}
struct NameViewer: View {
@Environment( \.presentationMode ) var presentationMode
@Environment( \.managedObjectContext ) private var moc
@State private var name: String = ""
@State private var reason: TrustReason = .unknown
var itemID: NSManagedObjectID?
var body: some View {
Form {
Section( header: Text( "Information" ) ) {
TextField( "Name", text: $name )
}
Section( header: Text( "Trust" ) ) {
Picker( "Reason", selection: $reason ) {
ForEach( TrustReason.allCases ) { trustReason in
Text( trustReason.title ).tag( trustReason )
}
}
}
}
.toolbar {
Button() {
if ( saveName() ) {
self.presentationMode.wrappedValue.dismiss()
}
} label: {
Text( "Save" )
}
}
.onAppear {
print( "on appear" )
guard let theID = itemID,
let item = moc.object( with: theID ) as? Item else {
return
}
print( "passed guard" )
if let itemName = item.name {
name = itemName
}
print( name )
}
}
private func saveName() -> Bool {
let item = Item( context: moc )
do {
print( self.name )
item.name = self.name
try moc.save()
return true
} catch {
print( error )
print( error.localizedDescription )
}
self.moc.rollback();
return false
}
}
struct NameViewer_Previews: PreviewProvider {
static var previews: some View {
NameViewer()
}
}
我可以创建要显示在 ContentView 列表中的新项目。
然后，当我选择列表中的某个项目时，我将该项目传递给 NameViewer。我可以确认我在 .onAppear 代码中成功找到了正确的对象。
然而，存在两个问题：
-
如果我在列表中选择一个项目，则项目名称不会出现在名称文本字段中，除非我先单击文本字段。
-
使用 .onAppear 似乎不是放置该代码的正确位置。原因是选取器将另一个视图推送到堆栈上，一旦选取该项目，.onAppear 会再次运行，并且我会丢失对名称字段的更改名称。
我该如何更改代码来解决这些问题？
