枚举案例'...'不是"......"类型的成员

Question

我有一个枚举:

enum State {
    case FullOpen
    case HalfOpen
    case Closed
}

而这段代码:

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
    }
}

我在每个switch语句中都出错:

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

我真的不明白为什么.有人可以解释一下吗？

Answer 1

这样它会工作正常:

if true {
    previousState = stateForConversionView

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

你需要添加!.

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