从词典创建Swift对象 [英] Create a Swift Object from a Dictionary

问题描述

如何根据Swift中字典中的查找值动态实例化一个类型？

How do you instantiate a type dynamically based upon a lookup value in a dictionary in Swift?

推荐答案

希望这对他人有用。它需要一些研究来证明这一点。目标是避免巨型if或switch语句的反模式从一个值创建每个对象类型。

Hopefully this is useful to others. It took some research to figure this out. The goal is to avoid the anti-pattern of giant if or switch statements to create each object type from a value.

class NamedItem : CustomStringConvertible {
    let name : String

    required init() {
        self.name = "Base"
    }

    init(name : String) {
        self.name = name
    }

    var description : String { // implement Printable
        return name
    }
}

class File : NamedItem {
    required init() {
        super.init(name: "File")
    }
}

class Folder : NamedItem {
    required init() {
        super.init(name: "Folder")
    }
}

// using self to instantiate.
let y = Folder.self
"\(y.init())"

let z = File.self
"\(z.init())"

// now put it in a dictionary.
enum NamedItemType {
    case Folder
    case File
}

var typeMap : [NamedItemType : NamedItem.Type] = [.Folder : Folder.self,
                                                  .File : File.self]
let p = typeMap[.Folder]
"\(p!.init())"
let q = typeMap[.File]
"\(q!.init())"

有趣的方面：​​

Interesting aspects:

• 对初始化器使用必需


• 使用。键入以获取字典值的类型。


• 使用.self获取可以实例化的类


• 使用（）来实例化动态对象。
  
• 使用可打印协议来获取隐式字符串值。


• 如何使用非参数化的初始化，并从子类初始化中获取值。

• use of "required" for initializers
• use of .Type to get the type for the dictionary value.
• use of .self to get the "class" that can be instantiated
• use of () to instantiate the dynamic object.
• use of Printable protocol to get implicit string values.
• how to init using a non parameterized init and get the values from subclass initialization.

更新为Swift 3.0语法

Updated to Swift 3.0 syntax

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