枚举案例“...”不是“...”类型的成员

Question

I have an enum:

enum State {
    case FullOpen
    case HalfOpen
    case Closed
}

and this code:

var stateForConversionView: State!
...


var previousState: State!

if true {
    previousState = stateForConversionView!
    switch previousState {
    case .FullOpen:
        stateForConversionView = .HalfOpen
    case .HalfOpen:
        stateForConversionView = .FullOpen
    case .Closed:
        stateForConversionView = .HalfOpen
    default:
        break
    }
}

I got an error on each switch statement:

Enum case 'FullOpen' not found in type 'State!'
Enum case 'HalfOpen' not found in type 'State!'
Enum case 'Closed' not found in type 'State!'

I don't really understand why. Can someone explain me please?

Answer 1

This way It will work fine :

if true {
    previousState = stateForConversionView

    switch previousState! {
    case .FullOpen:
        stateForConversionView = .HalfOpen
    case .HalfOpen:
        stateForConversionView = .FullOpen
    case .Closed:
        stateForConversionView = .HalfOpen
    default:
        break
    }
}

You need to add ! .

For more info refer THIS .

Answer 2

If the condition variable is in a different type of the "State". You should use rawValue property.

var previousState:String
previousState = stateForConversionView
 switch previousState {
        case State.FullOpen.rawValue:
            stateForConversionView = .HalfOpen
        case State.HalfOpen.rawValue:
            stateForConversionView = .FullOpen
        case State.Closed.rawValue:
            stateForConversionView = .HalfOpen
        default:break

        }

Answer 3

You can add ? at the end of case state.

if true {
    previousState = stateForConversionView

    switch previousState {
    case .FullOpen?:
        stateForConversionView = .HalfOpen
    case .HalfOpen?:
        stateForConversionView = .FullOpen
    case .Closed?:
        stateForConversionView = .HalfOpen
    default:
        break
    }
}

or .some(Error)

if true {
    previousState = stateForConversionView

    switch previousState {
    case .some(.FullOpen):
        stateForConversionView = .HalfOpen
    case .some(.HalfOpen):
        stateForConversionView = .FullOpen
    case .some(.Closed):
        stateForConversionView = .HalfOpen
    default:
        break
    }
}

Answer 4

You don't need to create a temporary variable( previousState ). Just unwrap the property that you are using as enum:

if true {
    switch stateForConversionView! {
    case .FullOpen:
        stateForConversionView = .HalfOpen
    case .HalfOpen:
        stateForConversionView = .FullOpen
    case .Closed:
        stateForConversionView = .HalfOpen
    default:
        break
    }
}