如何使枚举符合 Swift 中的可识别协议？

Question

I'm trying to make a list with the raw values of the cases from an enumeration with the new SwiftUI framework. However, I'm having a trouble with conforming the 'Data' to Identifiable protocol and I really cannot find information how to do it. It tells me "Initializer 'init(_:rowContent:)' requires that 'Data' conform to 'Identifiable'" The stub provides me with an ObjectIdentifier variable in the last extension, but don't know what should I return. Could you tell me how do it? How do I conform Data to Identifiable, so I can make a list with the raw values?

enum Data: String {
    case firstCase = "First string"
    case secondCase = "Second string"
    case thirdCase = "Third string"
}

extension Data: CaseIterable {
    static let randomSet = [Data.firstCase, Data.secondCase]
}

extension Data: Identifiable {
    var id: ObjectIdentifier {
        return //what?
    }

}

//-------------------------ContentView------------------------
import SwiftUI

struct Lala: View {
    var name: String

    var body: some View {
        Text(name)
    }
}

struct ContentView: View {
    var body: some View {
        return List(Data.allCases) { i in
            Lala(name: i.rawValue)
        }
    }
}

Answer 1

_{⚠️ Try not to use already used names like Data for your internal module. I will use MyEnum instead in this answer}

---

When something conforms to Identifiable , it must return something that can be identified by that. So you should return something unique to that case. For String base enum , rawValue is the best option you have:

extension MyEnum: Identifiable {
    var id: RawValue { rawValue }
}

Also, enum s can usually be identified by their selves:

extension MyEnum: Identifiable {
    var id: Self { self }
}

⚠️ Note 1 : If you return something that is unstable, like UUID() or an index , this means you get a new object each time you get the object and this will kill reusability and can cause epic memory and layout process usage beside view management issues like transition management and etc.

Take a look at this weird animation for adding a new pet:

Note 2 : From Swift 5.1, single-line closures don't need the return keyword.

Note 3 : Try not to use globally known names like Data for your own types. At least use namespace for that like MyCustomNameSpace.Data

---

Inline mode

You can make any collection iterable inline by one of it's element's keypath:

For example to self :

List(MyEnum.allCases, id:\.self)

or to any other compatible keypath:

List(MyEnum.allCases, id:\.rawValue)

---

✅ The checklist of the identifier: (from WWDC21)

• Exercise caution with random identifiers.
• Use stable identifiers.
• Ensure the uniqueness, one identifier per item.

Answer 2

You can try this way:

enum MyEnum: Identifiable {
    case valu1, valu2
    
    var id: Int {
        get {
            hashValue
        }
    }
}

Answer 3

Another approach with associated values would be to do something like this, where all the associated values are identifiable.

enum DataEntryType: Identifiable {
    var id: String {
        switch self {
        case .thing1ThatIsIdentifiable(let thing1):
            return thing1.id
        case .thing2ThatIsIdentifiable(let thing2):
            return thing2.id
        }
    }
    
    case thing1ThatIsIdentifiable(AnIdentifiableObject)
    case thing2ThatIsIdentifiable(AnotherIdentifiableObject)

Answer 4

Copyright © 2021 Mark Moeykens. All rights reserved. | @BigMtnStudio Combine Mastery in SwiftUI book

enum InvalidAgeError: String, Error , Identifiable {
    var id: String { rawValue }
    case lessThanZero = "Cannot be less than zero"
    case moreThanOneHundred = "Cannot be more than 100"
}

Answer 5

I'm trying to make a list with the raw values of the cases from an enumeration with the new SwiftUI framework. However, I'm having a trouble with conforming the 'Data' to Identifiable protocol and I really cannot find information how to do it. It tells me "Initializer 'init(_:rowContent:)' requires that 'Data' conform to 'Identifiable'" The stub provides me with an ObjectIdentifier variable in the last extension, but don't know what should I return. Could you tell me how do it? How do I conform Data to Identifiable, so I can make a list with the raw values?

enum Data: String {
    case firstCase = "First string"
    case secondCase = "Second string"
    case thirdCase = "Third string"
}

extension Data: CaseIterable {
    static let randomSet = [Data.firstCase, Data.secondCase]
}

extension Data: Identifiable {
    var id: ObjectIdentifier {
        return //what?
    }

}

//-------------------------ContentView------------------------
import SwiftUI

struct Lala: View {
    var name: String

    var body: some View {
        Text(name)
    }
}

struct ContentView: View {
    var body: some View {
        return List(Data.allCases) { i in
            Lala(name: i.rawValue)
        }
    }
}