快速将 if else 结构转换为 switch case

Question

我是编程新手，我正在尝试将这种 if else 结构转换为 Swift 语言的 Switch 案例，感谢您的帮助，谢谢。

这是我的代码

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if (segue.identifier == "ShowDefinition") {
        if let destinationViewController = segue.destinationViewController as? EnglishViewController {
            if let definition = sender as? String {
                if definition == "Abstraction" {
                    destinationViewController.titleMsg = "Abstraction"
                    destinationViewController.definitionMsg = "definition 1"
                } else if definition == "Binary System" {
                    destinationViewController.titleMsg = "Binary System"
                    destinationViewController.definitionMsg = "definition 2"
                } else if definition == "Computer" {
                    destinationViewController.titleMsg = "Computer"
                    destinationViewController.definitionMsg = "definition 3"

                } else if definition == "Internet" {
                    destinationViewController.titleMsg = "Internet"
                    destinationViewController.definitionMsg = "definition 4"

                } else if definition == "Virtual Reality" {
                    destinationViewController.titleMsg = "Virtual Reality"
                    destinationViewController.definitionMsg = "definition 5"

                }
            }
        }
    }
}

Answer 1

类似这样的：

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if (segue.identifier == "ShowDefinition") {
        if let destinationViewController = segue.destinationViewController as? EnglishViewController {
            if let definition = sender as? String {
                switch definition {
                case "Abstraction":
                    destinationViewController.titleMsg = "Abstraction"
                    destinationViewController.definitionMsg = "definition 1"
                case "Binary System":
                    destinationViewController.titleMsg = "Binary System"
                    destinationViewController.definitionMsg = "definition 2"
                case "Computer":
                    destinationViewController.titleMsg = "Computer"
                    destinationViewController.definitionMsg = "definition 3"
                case "Internet":
                    destinationViewController.titleMsg = "Internet"
                    destinationViewController.definitionMsg = "definition 4"
                    destinationViewController.titleMsg = "Abstraction"
                    destinationViewController.definitionMsg = "definition 1"
                case "Virtual Reality":
                    destinationViewController.titleMsg = "Virtual Reality"
                    destinationViewController.definitionMsg = "definition 5"
                default:
                    destinationViewController.titleMsg = ""
                    destinationViewController.definitionMsg = ""
                }
            }
        }
    }
}

检查你想对default 值做什么，如果没有一个case 匹配，就会被命中。

Answer 2

由于titeMsg 将始终包含definition 字符串，因此您可以使代码更短

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
  if segue.identifier == "ShowDefinition" {
    if let destinationViewController = segue.destinationViewController as? EnglishViewController {
      if let definition = sender as? String {
        switch definition {
        case "Abstraction":
          destinationViewController.definitionMsg = "definition 1"
        case "Binary System":
          destinationViewController.definitionMsg = "definition 2"
        case "Computer":
          destinationViewController.definitionMsg = "definition 3"
        case "Internet":
          destinationViewController.definitionMsg = "definition 4"
        case "Virtual Reality":
          destinationViewController.definitionMsg = "definition 5"
        default :
          destinationViewController.definitionMsg = "n/a"

        }
        destinationViewController.titleMsg = definition
      }
    }
  }
}

你可以更进一步，声明一个案例的枚举

enum Definitions : String {
  case Abstraction, BinarySystem = "Binary System", Computer, Internet, VirtualReality = "Virtual Reality"
}

这会保存default 语句，因为案例是详尽的。

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
  if (segue.identifier == "ShowDefinition") {
    if let destinationViewController = segue.destinationViewController as? EnglishViewController {
      if let definition = sender as? String, let definitionEnum = Definitions(rawValue:definition) {
        switch definitionEnum {
        case .Abstraction:
          destinationViewController.definitionMsg = "definition 1"
        case .BinarySystem:
          destinationViewController.definitionMsg = "definition 2"
        case .Computer:
          destinationViewController.definitionMsg = "definition 3"
        case .Internet:
          destinationViewController.definitionMsg = "definition 4"
        case .VirtualReality:
          destinationViewController.definitionMsg = "definition 5"
        }
        destinationViewController.titleMsg = definition
      }
    }
  }
}

Answer 3

使用此代码

   override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if (segue.identifier == "ShowDefinition") {
        if let destinationViewController = segue.destinationViewController as? EnglishViewController {
            if let definition = sender as? String {
                switch definition {
                case "Abstraction":
                    destinationViewController.titleMsg = "Abstraction"
                    destinationViewController.definitionMsg = "definition 1"
                case "Binary System":
                    destinationViewController.titleMsg = "Binary System"
                    destinationViewController.definitionMsg = "definition 2"
                case "Computer":
                    destinationViewController.titleMsg = "Computer"
                    destinationViewController.definitionMsg = "definition 3"
                case "Internet":
                    destinationViewController.titleMsg = "Internet"
                    destinationViewController.definitionMsg = "definition 4"
                case "Virtual Reality":
                    destinationViewController.titleMsg = "Virtual Reality"
                    destinationViewController.definitionMsg = "definition 5"
                default:
                    // As per your requirement
                    break
                }
            }
        }
    }
}

Answer 4

在这个特定的用例中，您不必真正求助于串行 if-else 或 switch 块，因为测试仅涉及测试给定的 String 实例 (definition) 是否等于String 的给定列表的任何成员。

因为destinationViewController.titleMsg 被赋予与definition 相同的值（在匹配的情况下），而destinationViewController.definitionMsg 只是一个运行数字w.r.t。 String 列表的索引 (+1)，您可以在单个可选绑定子句中捕获所有逻辑：

let validTitles = ["Abstraction", "Binary System", "Computer", "Internet", "Virtual Reality"]
let definition = "Abstraction"

if let definitionAndTitle = validTitles.enumerated().filter({$1 == definition}).first {
    print("titleMsg=\(definitionAndTitle.1)")
    print("definitionMsg=\(definitionAndTitle.0 + 1)")
}

应用于您的示例（只需扩展您现有的可选绑定条款）

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if (segue.identifier == "ShowDefinition") {
        if let destinationViewController = segue.destinationViewController as? EnglishViewController {
            // or, better, keep this list of titles as e.g. a static
            // immutable property of your viewcontroller class, as these
            // should already be set at compile time.
            let validTitles = ["Abstraction", "Binary System",
                               "Computer", "Internet", "Virtual Reality"]
            if let definition = sender as? String, let defNum = 
                validTitles.enumerated().filter({$1 == definition}).first?.0 {
                destinationViewController.titleMsg = definition
                destinationViewController.definitionMsg = "definition \(defNum+1)"
            }
        }
    }
}