在Swift,AnyObject类型中解析json

Question

我正在尝试解析json,但我对数据类型有一些困难,特别是AnyObject类型+向下转换.

让我们考虑下面的json(它是一个完整的json的摘录).

{  "weather":
   [
      {
         "id":804,
         "main":"Clouds",
         "description":"overcast clouds",
         "icon":"04d"
      }
   ],
}

对我来说,json可以描述如下:

- json: Dictionary of type [String: AnyObject] (or NSDictionary, so = [NSObject, AnyObject] in Xcode 6 b3)
    - "weather": Array of type [AnyObject] (or NSArray)
         - Dictionary of type [String: AnyObject] (or NSDictionary, so = [NSObject, AnyObject] in Xcode 6 b3)

我的json是AnyObject类型!(我用来JSONObjectWithData从URL获取JSON).

然后我想访问天气词典.这是我写的代码.

var localError: NSError?
var json: AnyObject! = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &localError)

if let dict = json as? [String: AnyObject] {
 if let weatherDictionary = dict["weather"] as? [AnyObject] {
      // Do stuff with the weatherDictionary
    }
}

这是我得到的错误

Playground execution failed: error: <EXPR>:28:56: error: '[AnyObject]' is not a subtype of '(String, AnyObject)'
        if let weatherDictionary = dict["weather"] as? [AnyObject] {

我不明白为什么将dict ["weather"]与(String,AnyObject)的子类型进行比较而不是AnyObject.

我将我的字典声明为[String:AnyObject],所以我使用String键访问一个值,我应该有一个AnyObject,不是吗？

如果我使用NSDictionary而不是[String:AnyObject],它可以工作.

如果我使用NSArray而不是[AnyObject],它可以工作.

- The Xcode 6 beta 3 release notes tell that "NSDictionary* is now imported from Objective-C APIs as [NSObject : AnyObject].".
- And the Swift book: "When you bridge from an NSArray object to a Swift array, the resulting array is of type [AnyObject]."

编辑

我忘了强行解开字典["天气"]!

if let dict = json as? [String: AnyObject] {
    println(dict)
       if let weatherDictionary = dict["weather"]! as? [AnyObject] {
            println("\nWeather dictionary:\n\n\(weatherDictionary)")
            if let descriptionString = weatherDictionary[0]["description"]! as? String {
                println("\nDescription of the weather is: \(descriptionString)")
        }
    }
}

请注意,我们应该仔细检查是否存在第一个Optional.

if let dict = json as? [String: AnyObject] {
    for key in ["weather", "traffic"] {
        if let dictValue = dict[key] {
            if let subArray = dictValue as? [AnyObject] {
                println(subArray[0])
            }
        } else {
            println("Key '\(key)' not found")
        }
    }
}

Answer 1

这对我在操场和终端使用都很好 env xcrun swift

更新SWIFT 4和CODABLE

这是使用Codable协议的Swift 4示例.

var jsonStr = "{\"weather\":[{\"id\":804,\"main\":\"Clouds\",\"description\":\"overcast clouds\",\"icon\":\"04d\"}],}"

struct Weather: Codable {
    let id: Int
    let main: String
    let description: String
    let icon: String
}

struct Result: Codable {
    let weather: [Weather]
}

do {
    let weather = try JSONDecoder().decode(Result.self, from: jsonStr.data(using: .utf8)!)
    print(weather)
}
catch {
    print(error)
}

更新SWIFT 3.0

我已经更新了Swift 3的代码,还展示了如何将解析后的JSON包装到对象中.感谢所有的投票!

import Foundation

struct Weather {
    let id: Int
    let main: String
    let description: String
    let icon: String
}

extension Weather {
    init?(json: [String: Any]) {
        guard
            let id = json["id"] as? Int,
            let main = json["main"] as? String,
            let description = json["description"] as? String,
            let icon = json["icon"] as? String
        else { return nil }
        self.id = id
        self.main = main
        self.description = description
        self.icon = icon
    }
}

var jsonStr = "{\"weather\":[{\"id\":804,\"main\":\"Clouds\",\"description\":\"overcast clouds\",\"icon\":\"04d\"}],}"

enum JSONParseError: Error {
    case notADictionary
    case missingWeatherObjects
}

var data = jsonStr.data(using: String.Encoding.ascii, allowLossyConversion: false)
do {
    var json = try JSONSerialization.jsonObject(with: data!, options: [])
    guard let dict = json as? [String: Any] else { throw JSONParseError.notADictionary }
    guard let weatherJSON = dict["weather"] as? [[String: Any]] else { throw JSONParseError.missingWeatherObjects }
    let weather = weatherJSON.flatMap(Weather.init)
    print(weather)
}
catch {
    print(error)
}

- 以前的答案 -

import Foundation

var jsonStr = "{\"weather\":[{\"id\":804,\"main\":\"Clouds\",\"description\":\"overcast clouds\",\"icon\":\"04d\"}],}"
var data = jsonStr.dataUsingEncoding(NSASCIIStringEncoding, allowLossyConversion: false)
var localError: NSError?
var json: AnyObject! = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: &localError)

if let dict = json as? [String: AnyObject] {
    if let weather = dict["weather"] as? [AnyObject] {
        for dict2 in weather {
            let id = dict2["id"]
            let main = dict2["main"]
            let description = dict2["description"]
            println(id)
            println(main)
            println(description)
        }
    }
}

由于我仍然在为这个答案获得投票,我想我会为Swift 2.0重新审视它:

import Foundation

var jsonStr = "{\"weather\":[{\"id\":804,\"main\":\"Clouds\",\"description\":\"overcast clouds\",\"icon\":\"04d\"}],}"
var data = jsonStr.dataUsingEncoding(NSASCIIStringEncoding, allowLossyConversion: false)
do {
    var json = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers)

    if let dict = json as? [String: AnyObject] {
        if let weather = dict["weather"] as? [AnyObject] {
            for dict2 in weather {
                let id = dict2["id"] as? Int
                let main = dict2["main"] as? String
                let description = dict2["description"] as? String
                print(id)
                print(main)
                print(description)
            }
        }
    }

}
catch {
    print(error)
}

最大的区别是变量json不再是可选类型和do/try/catch语法.我还继续和类型id,main以及description.

Answer 2

尝试:

• https://github.com/dankogai/swift-json

有了它,你可以这样:

let obj:[String:AnyObject] = [
    "array": [JSON.null, false, 0, "", [], [:]],
    "object":[
        "null":   JSON.null,
        "bool":   true,
        "int":    42,
        "double": 3.141592653589793,
        "string": "a ?\t?\n",
        "array":  [],
        "object": [:]
    ],
    "url":"http://blog.livedoor.com/dankogai/"
]

let json = JSON(obj)

json.toString()
json["object"]["null"].asNull       // NSNull()
json["object"]["bool"].asBool       // true
json["object"]["int"].asInt         // 42
json["object"]["double"].asDouble   // 3.141592653589793
json["object"]["string"].asString   // "a ?\t?\n"
json["array"][0].asNull             // NSNull()
json["array"][1].asBool             // false
json["array"][2].asInt              // 0
json["array"][3].asString           // ""