2022年，swift 5

扩展的使用:

编码:

if let json = statisticsDict.asJSONStr() {
     //your action with json
}

从字典解码:

json.decodeFromJson(type: [String:AppStat].self)
    .onSuccess{
        $0// your dictionary of type: [String:AppStat]
    }

扩展:

extension Dictionary where Key: Encodable, Value: Encodable {
    func asJSONStr() -> String? {
        let encoder = JSONEncoder()
        if let jsonData = try? encoder.encode(self) {
            if let jsonString = String(data: jsonData, encoding: .utf8) {
                return jsonString
            }
        }
        
        return nil
    }
}

public extension String {
    func decodeFromJson<T>(type: T.Type) -> Result<T, Error> where T: Decodable {
        self.asData()
            .flatMap { JSONDecoder().try(type, from: $0) }
    }

    func asData() -> Result<Data, Error> {
        if let data = self.data(using: .utf8) {
            return .success(data)
        } else {
            return .failure(WTF("can't convert string to data: \(self)"))
        }
    }
}

extension JSONDecoder {
    func `try`<T: Decodable>(_ t: T.Type, from data: Data) -> Result<T,Error> {
        do {
            return .success(try self.decode(t, from: data))
        } catch {
            return .failure(error)
        }
    }
}

你问题的答案如下:

斯威夫特2.1

     do {
          if let postData : NSData = try NSJSONSerialization.dataWithJSONObject(dictDataToBeConverted, options: NSJSONWritingOptions.PrettyPrinted){

          let json = NSString(data: postData, encoding: NSUTF8StringEncoding)! as String
          print(json)}

        }
        catch {
           print(error)
        }

斯威夫特5:

extension Dictionary {
    
    /// Convert Dictionary to JSON string
    /// - Throws: exception if dictionary cannot be converted to JSON data or when data cannot be converted to UTF8 string
    /// - Returns: JSON string
    func toJson() throws -> String {
        let data = try JSONSerialization.data(withJSONObject: self)
        if let string = String(data: data, encoding: .utf8) {
            return string
        }
        throw NSError(domain: "Dictionary", code: 1, userInfo: ["message": "Data cannot be converted to .utf8 string"])
    }
}

在Swift 5.4中

extension Dictionary {
    var jsonData: Data? {
        return try? JSONSerialization.data(withJSONObject: self, options: [.prettyPrinted])
    }
    
    func toJSONString() -> String? {
        if let jsonData = jsonData {
            let jsonString = String(data: jsonData, encoding: .utf8)
            return jsonString
        }
        
        return nil
    }
}

把它作为变量的想法是，这样你就可以像这样重用它:

extension Dictionary {
    func decode<T:Codable>() throws -> T {
        return try JSONDecoder().decode(T.self, from: jsonData ?? Data())
    }
}

斯威夫特3:

let jsonData = try? JSONSerialization.data(withJSONObject: dict, options: [])
let jsonString = String(data: jsonData!, encoding: .utf8)!
print(jsonString)

这是一个简单的扩展来做到这一点:

https://gist.github.com/stevenojo/0cb8afcba721838b8dcb115b846727c3

extension Dictionary {
    func jsonString() -> NSString? {
        let jsonData = try? JSONSerialization.data(withJSONObject: self, options: [])
        guard jsonData != nil else {return nil}
        let jsonString = String(data: jsonData!, encoding: .utf8)
        guard jsonString != nil else {return nil}
        return jsonString! as NSString
    }

}