Swift：flatMap to Dictionary

发布时间：2020-12-14 04:41:33 所属栏目：百科来源：网络整理

导读：我试图解析以下 JSON： { "String For Key 1": [ "Some String A","Some String B","Some String C",],"String For Key 2": [ "Some String D","Some String E","Some String F" ],"String For Key 3": [ "Some String G","Some String H","Some String I","

我试图解析以下 JSON：

{ 
  "String For Key 1": [
    "Some String A","Some String B","Some String C",],"String For Key 2": [
    "Some String D","Some String E","Some String F"
  ],"String For Key 3": [
    "Some String G","Some String H","Some String I","String For Key 4": [
    "Some String J","Some String K","Some String L"
  ],"String For Key 5": [
    "Some String M","Some String N","Some String O"
  ],"String For Key 6": [
    "Some String P","Some String Q","Some String R"
  ]
}

我也关注这个tutorial.它在Playground的Github上

在示例中,他们使用typealias JSONDictionary = [String：AnyObject]解析字典数组

我需要解析一个具有Key的字典,这个字符串是String,而Value是一个Array.因此：typealias JSONDictionary = [String：[AnyObject]],我在返回flatMap时遇到错误.

extension Resource {
    init(url: NSURL,parseJSON: AnyObject -> A?) {
        self.url = url
        self.parse = { data in
            let json = try? NSJSONSerialization.JSONObjectWithData(data,options: []) as? [String: [AnyObject]]
           //This is where I get an error
            return json.flatMap(parseJSON)
        }
    }
}

错误：

Cannot convert value of type `AnyObject -> A? to expected argument type `([String: [AnyObject]]?) -> _?

如何获得一个字符串,字符串为String,值为数组？我想保留他们的通用方法.

解决方法

jsonString的类型是Dictionary< String,Array< String>>
你可以给它一个像Dictionary< String,AnyObject>这样的类型.

AnyObject可以包含类和结构,即Array,Dictionary,String,Int,Obj C Classes
因此,一个数组< String>由AnyObject表示而不是[AnyObject]

let jsonString:[String: AnyObject] =
[
    "String For Key 1": [
    "http://www.urlToSomePathA.jpg","http://www.urlToSomePathB.jpg","http://www.urlToSomePathC.jpg","String For Key 2": [
    "http://www.urlToSomePathD.jpg","http://www.urlToSomePathE.jpg","http://www.urlToSomePathF.jpg"
    ]
]

// Now you can map a function on the value type
let values = jsonString.flatMap { $0.1 as? [String] }
print(values)
// RESULT: [["http://www.urlToSomePathA.jpg","http://www.urlToSomePathC.jpg"],["http://www.urlToSomePathD.jpg","http://www.urlToSomePathF.jpg"]]

更新

let keys = jsonString.flatMap { $0.0 } // ["String For Key 1","String For Key 2"]

正如@dffri所评论的那样,你可以在字典上使用keys属性,它将返回LazyMapCollection,只有当你访问里面的对象时才会实现.

let keys = jsonString.keys

（编辑：李大同）

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