Question

我有一个这样设置的枚举：

enum Calculators {

    case RECTANGLE
    case CIRCLE
    case TRIANGLE
    case TRAPEZOID
    case CUBE
    case CONE
    case SPHERE
    case CYLINDER
    case ASPHALT
    case TACK_SEAL_COAT
    case ASPHALT_YIELD
    case SIDEWALK
    case CONCRETE_DECK_SEALER
    case CHIP_SEAL
    case AGGREGATE_STOCK_PILE
    case BACKFILL
    case SALT_STOCK_PILE
    case SALT_SPREADER_CALIBRATION
    case ROAD_SALT_APPLICATION

    static let groups = [[RECTANGLE, CIRCLE, TRIANGLE, TRAPEZOID],
                       [CUBE, CONE, SPHERE, CYLINDER],
                       [ASPHALT, TACK_SEAL_COAT, ASPHALT_YIELD, SIDEWALK, CONCRETE_DECK_SEALER, CHIP_SEAL, AGGREGATE_STOCK_PILE, BACKFILL],
                       [SALT_STOCK_PILE, SALT_SPREADER_CALIBRATION, ROAD_SALT_APPLICATION]]

    func getCalculator(category: Int, row: Int) -> Calculators {
        if let calculator =  Calculators.groups[category][row] {
            return calculator
        } else {
            return Calculators.UNDEFINED
        }
    }
}

我的想法是，我将传递我想要的计算器类别，然后是特定的计算器，它将返回正确的枚举，所有这些都基于TableView中选择的行。

问题在于我遇到了一个令人困惑的错误。第一个错误发生在if let calculator行。错误显示为Enum case 'Some' not found in type 'Calculators'。我不确定为什么要这样做。

这个错误意味着什么，我该如何解决它？

Answer 1

您的if let未评估可选项（必需）。数组下标如果超出范围则会崩溃。我想你的意思是：

func getCalculator(category: Int, row: Int) -> Calculators? {
    let groups = Calculators.groups
    guard groups.indices.contains(category) else { return nil }
    let calculatorCateogry = groups[category]
    guard calculatorCateogry.indices.contains(row) else { return nil }
    return calculatorCateogry[row]
}

Answer 2

很少有事情 1.添加UNDEFINED作为其中一个案例 2.你也可以将getCalculator声明为静态方法来访问它，如Calculators.getCalculator

为了防止程序在索引超出范围时崩溃，我添加了将返回UNDEFINED的检查。

enum Calculators {
    case RECTANGLE
    case CIRCLE
    case TRIANGLE
    case TRAPEZOID
    case CUBE
    case CONE
    case SPHERE
    case CYLINDER
    case ASPHALT
    case TACK_SEAL_COAT
    case ASPHALT_YIELD
    case SIDEWALK
    case CONCRETE_DECK_SEALER
    case CHIP_SEAL
    case AGGREGATE_STOCK_PILE
    case BACKFILL
    case SALT_STOCK_PILE
    case SALT_SPREADER_CALIBRATION
    case ROAD_SALT_APPLICATION
    case UNDEFINED

    static let groups = [[RECTANGLE, CIRCLE, TRIANGLE, TRAPEZOID],
                     [CUBE, CONE, SPHERE, CYLINDER],
                     [ASPHALT, TACK_SEAL_COAT, ASPHALT_YIELD, SIDEWALK, CONCRETE_DECK_SEALER, CHIP_SEAL, AGGREGATE_STOCK_PILE, BACKFILL],
                     [SALT_STOCK_PILE, SALT_SPREADER_CALIBRATION, ROAD_SALT_APPLICATION]]

func getCalculator(category: Int, row: Int) -> Calculators {
     if Calculators.groups.indices.contains(category) {
         let calculators = Calculators.groups[category]

         if calculators.indices.contains(row) {
            return calculators[row]
         }

     }
    return Calculators.UNDEFINED
 }
}

let testCalculator = Calculators.RECTANGLE
testCalculator.getCalculator(category: 7, row: 1) // Result: UNDEFINED
testCalculator.getCalculator(category: 1, row: 1) // Result: CONE

枚举函数内部的错误

2 个答案: