Swift編程中的一些類型轉(zhuǎn)換方法詳解

更新時間：2015年11月07日 18:14:11 投稿：goldensun

這篇文章主要介紹了Swift編程中的一些類型轉(zhuǎn)換方法詳解,是Swift入門學(xué)習(xí)中的基礎(chǔ)知識,需要的朋友可以參考下

驗(yàn)證一個實(shí)例的類型'類型轉(zhuǎn)換'在 Swift 語言編程中。它是用來檢查實(shí)例類型是否屬于特定超類或子類或其自己的層次結(jié)構(gòu)定義。

Swift 類型轉(zhuǎn)換提供兩個操作符：“is” 檢查值的類型和 'as' 將類型值轉(zhuǎn)換為不同的類型值。類型轉(zhuǎn)換還檢查實(shí)例類型是否符合特定的協(xié)議一致性標(biāo)準(zhǔn)。

定義一個類層次結(jié)構(gòu)
類型轉(zhuǎn)換用于檢查實(shí)例的類型或者它屬于特定類型。此外，檢查類和它的子類層次結(jié)構(gòu)來檢查并轉(zhuǎn)換這些實(shí)例，使之作為一個相同的層次結(jié)構(gòu)。

復(fù)制代碼代碼如下:

class Subjects {
   var physics: String
   init(physics: String) {
      self.physics = physics
   }
}

class Chemistry: Subjects {
   var equations: String
   init(physics: String, equations: String) {
      self.equations = equations
      super.init(physics: physics)
   }
}

class Maths: Subjects {
   var formulae: String
   init(physics: String, formulae: String) {
      self.formulae = formulae
      super.init(physics: physics)
   }
}

let sa = [
Chemistry(physics: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")]

let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")

let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")

當(dāng)我們使用 playground 運(yùn)行上面的程序，得到以下結(jié)果。

Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz

類型檢查
進(jìn)行類型檢查，用 'is' 操作符。在 'is' 操作符檢查類型實(shí)例是否屬于特定的子類型，如果它屬于該實(shí)例返回“true”，否則將返回“false”。

復(fù)制代碼代碼如下:

class Subjects {
   var physics: String
   init(physics: String) {
      self.physics = physics
   }
}

class Chemistry: Subjects {
   var equations: String
   init(physics: String, equations: String) {
      self.equations = equations
      super.init(physics: physics)
   }
}

class Maths: Subjects {
   var formulae: String
   init(physics: String, formulae: String) {
      self.formulae = formulae
      super.init(physics: physics)
   }
}

let sa = [
   Chemistry(physics: "solid physics", equations: "Hertz"),
   Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz"),
   Chemistry(physics: "Thermo physics", equations: "Decibels"),
   Maths(physics: "Astro Physics", formulae: "MegaHertz"),
   Maths(physics: "Differential Equations", formulae: "Cosine Series")]

let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")

let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")

var chemCount = 0
var mathsCount = 0
for item in sa {
   if item is Chemistry {
      ++chemCount
   } else if item is Maths {
      ++mathsCount
   }
}

println("Subjects in chemistry contains \(chemCount) topics and maths contains \(mathsCount) topics")

當(dāng)我們使用 playground 運(yùn)行上面的程序，得到以下結(jié)果。

Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Subjects in chemistry contains 2 topics and maths contains 3 topics

向下轉(zhuǎn)換
向下類型轉(zhuǎn)換的子類型可以有兩個操作符（如：as? 和 as!）。as? 當(dāng)值是nil，返回一個可選值。它是用來檢查成功向下轉(zhuǎn)型。

“as!” 返回強(qiáng)制解包裹，如可選鏈，向下轉(zhuǎn)換返回 nil 值。它用來觸發(fā)運(yùn)行時錯誤在向下轉(zhuǎn)型出現(xiàn)故障時

復(fù)制代碼代碼如下:

class Subjects {
   var physics: String
   init(physics: String) {
      self.physics = physics
   }
}

class Chemistry: Subjects {
   var equations: String
   init(physics: String, equations: String) {
      self.equations = equations
      super.init(physics: physics)
   }
}

class Maths: Subjects {
   var formulae: String
   init(physics: String, formulae: String) {
      self.formulae = formulae
      super.init(physics: physics)
   }
}

let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")

let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")

var chemCount = 0
var mathsCount = 0

for item in sa {
   if let print = item as? Chemistry {
      println("Chemistry topics are: '\(print.physics)', \(print.equations)")
   } else if let example = item as? Maths {
      println("Maths topics are: '\(example.physics)', \(example.formulae)")
   }
}

當(dāng)我們使用 playground 運(yùn)行上面的程序，得到以下結(jié)果。

Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Chemistry topics are: 'solid physics', Hertz
Maths topics are: 'Fluid Dynamics', Giga Hertz
Chemistry topics are: 'Thermo physics', Decibels
Maths topics are: 'Astro Physics', MegaHertz
Maths topics are: 'Differential Equations', Cosine Series

類型轉(zhuǎn)換：任何與任何對象
為了表示實(shí)例屬于任何類型包括函數(shù)類型，使用“Any”關(guān)鍵字

復(fù)制代碼代碼如下:

class Subjects {
   var physics: String
   init(physics: String) {
      self.physics = physics
   }
}

class Chemistry: Subjects {
   var equations: String
   init(physics: String, equations: String) {
      self.equations = equations
      super.init(physics: physics)
   }
}

class Maths: Subjects {
   var formulae: String
   init(physics: String, formulae: String) {
      self.formulae = formulae
      super.init(physics: physics)
   }
}

let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")

let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")

var chemCount = 0
var mathsCount = 0

var exampleany = [Any]()

exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Example for Any")
exampleany.append(Chemistry(physics: "solid physics", equations: "Hertz"))

for print in exampleany {
   switch print {
   case let someInt as Int:
      println("Integer value is \(someInt)")
   case let someDouble as Double where someDouble > 0:
      println("Pi value is \(someDouble)")
   case let someString as String:
      println("\(someString)")
   case let phy as Chemistry:
      println("Topics '\(phy.physics)', \(phy.equations)")
   default:
      println("None")
   }
}

當(dāng)我們使用 playground 運(yùn)行上面的程序，得到以下結(jié)果。

Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Chemistry topics are: 'solid physics', Hertz
Maths topics are: 'Fluid Dynamics', Giga Hertz
Chemistry topics are: 'Thermo physics', Decibels
Maths topics are: 'Astro Physics', MegaHertz
Maths topics are: 'Differential Equations', Cosine Series
Integer value is 12
Pi value is 3.14159
Example for Any
Topics 'solid physics', Hertz
AnyObject

為了表示是任何類型的類實(shí)例，使用AnyObject“關(guān)鍵字

復(fù)制代碼代碼如下:

class Subjects {
   var physics: String
   init(physics: String) {
      self.physics = physics
   }
}

class Chemistry: Subjects {
   var equations: String
   init(physics: String, equations: String) {
      self.equations = equations
      super.init(physics: physics)
   }
}

class Maths: Subjects {
   var formulae: String
   init(physics: String, formulae: String) {
      self.formulae = formulae
      super.init(physics: physics)
   }
}

let saprint: [AnyObject] = [Chemistry(physics: "solid physics", equations: "Hertz"),
   Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz"),
   Chemistry(physics: "Thermo physics", equations: "Decibels"),
   Maths(physics: "Astro Physics", formulae: "MegaHertz"),
   Maths(physics: "Differential Equations", formulae: "Cosine Series")]

let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
println("Instance physics is: \(samplechem.physics)")
println("Instance equation is: \(samplechem.equations)")

let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
println("Instance physics is: \(samplemaths.physics)")
println("Instance formulae is: \(samplemaths.formulae)")

var chemCount = 0
var mathsCount = 0

for item in saprint {
   if let print = item as? Chemistry {
      println("Chemistry topics are: '\(print.physics)', \(print.equations)")
   } else if let example = item as? Maths {
      println("Maths topics are: '\(example.physics)', \(example.formulae)")
   }
}

var exampleany = [Any]()
exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Example for Any")
exampleany.append(Chemistry(physics: "solid physics", equations: "Hertz"))

當(dāng)我們使用 playground 運(yùn)行上面的程序，得到以下結(jié)果。

Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz
Chemistry topics are: 'solid physics', Hertz
Maths topics are: 'Fluid Dynamics', Giga Hertz
Chemistry topics are: 'Thermo physics', Decibels
Maths topics are: 'Astro Physics', MegaHertz
Maths topics are: 'Differential Equations', Cosine Series
Integer value is 12
Pi value is 3.14159
Example for Any
Topics 'solid physics', Hertz

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