使用SwiftUI ForEach从NSOrderedSet获取字符串值 [英] Getting a String value from NSOrderedSet using SwiftUI ForEach

问题描述

使用此问题/答案我能够使用ForEach来使用从中创建的NSOrderedSet在CoreData中是一对多关系，但是我似乎无法访问存储在Core Data实体中的字符串属性。

Using this question/answer I am able to use ForEach to use a NSOrderedSet created from a One to Many relationship in CoreData, however I can't seem to access a String Attribute stored in the Core Data entity.

我有两个CoreData实体：Client& SessionNote。客户端可以有很多SessionNotes，clientNotes的NSOrderedSet，而SessionNote只能有一个Client。

I have two CoreData entities: Client & SessionNote. Clients can have many SessionNotes, the NSOrderedSet of clientNotes, and SessionNote can only have one Client.

Client + CoreDataClass.swift：

Client+CoreDataClass.swift:

public class Client: NSManagedObject {

}

Client + CoreDataProperties.swift：

Client+CoreDataProperties.swift:

extension Client {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Client> {
        return NSFetchRequest<Client>(entityName: "Client")
    }

    @NSManaged public var firstName: String?
    @NSManaged public var lastName: String?
    @NSManaged public var id: UUID?
    @NSManaged public var clientNotes: NSOrderedSet?

}

SessionNote + CoreDataClass.swift：

SessionNote+CoreDataClass.swift:

public class SessionNote: NSManagedObject {

}

SessionNote + CoreDataProperties.swift：

SessionNote+CoreDataProperties.swift:

extension SessionNote {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<SessionNote> {
        return NSFetchRequest<SessionNote>(entityName: "SessionNote")
    }

    @NSManaged public var date: Date?
    @NSManaged public var noteText: String?
    @NSManaged public var id: UUID?
    @NSManaged public var clientOrigin: Client?

}

这是ClientDetailView.swift：

and here is ClientDetailView.swift:

struct ClientDetailView: View {

    @Environment(\.managedObjectContext) var moc

    @ObservedObject var selectedClient: Client


    var body: some View {
        Form {
            HStack {
                Text("\(selectedClient.firstName ?? "") \(selectedClient.lastName ?? "")")
            }
            Section() {
                ForEach(Array(selectedClient.clientNotes!.set), id: \.self) { note in
                    Text("This will repeat for the number of notes in the clientNotes NSOrderedSet")
                    /*
                     But instead I want to be able to display the noteText
                     string attribute stored in the SessionNote CoreData entity
                     instead of the above placeholder.
                    */
                }
            }

        }

    }
}

我尝试过 Text（ \（note.noteText ??））但会引发以下错误：

I've tried Text("\(note.noteText ?? "")") but it throws the following error:

类型 AnyHashable的值没有成员 noteText

Value of type 'AnyHashable' has no member 'noteText'

当我尝试 Text（ \（self.selectedClient.clientNotes！.value（forKeyPath：\SessionNote.noteText））） 它将引发以下错误：

When I tried Text("\(self.selectedClient.clientNotes!.value(forKeyPath: \SessionNote.noteText))") it throws the following error:

协议类型'Any'无法符合'_FormatSpecifiable'，因为只有具体类型可以符合协议

Protocol type 'Any' cannot conform to '_FormatSpecifiable' because only concrete types can conform to protocols

是否仍要为每个SessionNote noteText实体显示不同的String值？

Is there anyway to display the different String values for each of the SessionNote noteText entity?

推荐答案

您可以在 NSOrderedSet array 方法c>并将其强制类型转换为 [SessionNote] ，因为您知道您将始终将 SessionNote 类存储到有序集合中。

You can use array method on NSOrderedSet and force typecast it to [SessionNote], since you know that you will always be storing SessionNote class to the ordered set.

ForEach(selectedClient.clientNotes!.array as! [SessionNote], id: \.self) { (note: SessionNote) in
    Text(note.text ?? "")
}

由于在您希望使用笔记的每个地方都必须进行此转换。您还可以在 Client 内添加一个计算属性，该属性始终为您提供 SessionNote 数组的键入版本。

Since this casting will be necessary in every places you wish to use the notes. You could also add a computed property inside your Client which always gives you typed version of the SessionNote array.

extension Client {
  var typedClientNotes: [SessionNote] {
    return (clientNotes?.array as? [SessionNote]) ?? []
  }
}

而且，通过这些新更改，您可以进行您的 ForEach 会更好。

And, with these new changes you can make your ForEach bit better.

ForEach(selectedClient.typedClientNotes, id: \.self) { note in
    Text(note.text ?? "")
}

由于这个原因，我尝试将普通的 Set 用于Core数据关系。因为它可以被键入并使使用Coredata变得非常有趣。但是，尽管 NSOrderedSet 有一个无类型的集合，但它具有自己的优势。

For this reason, I try to use normal Set for Core data relationship. Because it can be typed and makes working with Coredata so much fun. But, NSOrderedSet has its own advantages despite of being an untyped collection.

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