带范围的开关盒

Question

我正在学习 Swift，并在观看视频之前尝试自己编写 Ryan Wenderlich 的游戏“Bullseye”。

我需要根据用户与目标数字的接近程度来给他分数。我尝试计算差异，然后检查范围并向用户提供分数，这就是我使用 If-else 所做的（无法使用 switch case 做到这一点）：

private func calculateUserScore() -> Int {
    let diff = abs(randomNumber - Int(bullsEyeSlider.value))
    if diff == 0 {
        return PointsAward.bullseye.rawValue
    } else if diff < 10 {
        return PointsAward.almostBullseye.rawValue
    } else if diff < 30 {
        return PointsAward.close.rawValue
    }
    return 0 // User is not getting points. 
}

有没有更优雅的方法或者使用 Switch-Case？ 我不能只做

diff == 0

，例如在 switch case 中，因为 xCode 给了我一条错误消息。

Answer 1

这应该有效。

private func calculateUserScore() -> Int {
    let diff = abs(randomNumber - Int(bullsEyeSlider.value))
    switch diff {
    case 0:
        return PointsAward.bullseye.rawValue
    case 1..<10:
        return PointsAward.almostBullseye.rawValue
    case 10..<30:
        return PointsAward.close.rawValue
    default:
        return 0
    }
}

它位于《Swift 编程语言》一书中的“控制流”->“区间匹配”下。

Answer 2

where

而不是

if

看起来更干净，这会起作用

func isOutdated(days: Int) -> Outdated {

    var outdatedStatus = Outdated.none

    switch days {
    case _ where days < 5:
        outdatedStatus = .tooLow
    case 5...10:
        outdatedStatus = .low
    case 11...20:
        outdatedStatus = .high
    case _ where days > 20:
        outdatedStatus = .expired
    default:
        outdatedStatus = .none
    }
    return outdatedStatus
}

在 Swift 5.9 新功能发布后，这可能会变得更简单：

func isOutdated(days: Int) -> Outdated {
    switch days {
    case _ where days < 5:
        .tooLow
    case 5...10:
        .low
    case 11...20:
        .high
    case _ where days > 20:
         .expired
    default:
         .none
    }
}

Answer 3

switch diff {
case 0:
    print("Bull Eye")
case 1..<10:
    print("Almost Bull Eye")
case 10..<30:
    print("Close")
default:
    print("Too Far")
}

Answer 4

enum PointsAward: Int {
    case close
    case almostBullseye
    case bullseye
}

private func calculateUserStory() -> Int {
    let bullsEyeSliderValue = 9
    let randomNumber = 100
    let diff = abs(randomNumber - Int(bullsEyeSliderValue))
    switch diff {
    case 0:
        return PointsAward.bullseye.rawValue
    case 0..<10:
        return PointsAward.almostBullseye.rawValue
    case 0..<30:
        return PointsAward.close.rawValue
    default: return 0
    }
}

Answer 5

a...b

// 范围从a到b，意味着b也包含在内

a..<b

// 范围从a到b-1，表示不包括b

private func calculateUserScore() -> Int {
    let diff = abs(randomNumber - Int(bullsEyeSlider.value))
    switch diff {
    case 0: return PointsAward.bullseye.rawValue
    case 1..<10: return PointsAward.almostBullseye.rawValue
    case 10..<30: return PointsAward.close.rawValue
    default: return 0
    }
}

Answer 6

   var progress: CGFloat!
   switch CGFloat(progress) {
    case 0 ... 0.25:
        barColor = .red
    case 0.25 ... 0.5:
        barColor = .yellow
    default:
        break
    }