Correctly Parsing JSON in Swift 3

Question

I m trying to fetch a JSON response and store the results in a variable  I ve had versions of this code work in previous releases of Swift  until the GM version of Xcode 8 was released  I had a look at a few similar posts on StackOverflow  Swift 2 Parsing JSON - Cannot subscript a value of type  AnyObject  and JSON Parsing in Swift 3    However  it seems the ideas conveyed there do not apply in this scenario   How do I correctly parse the JSON reponse in Swift 3   Has something changed in the way JSON is read in Swift 3   Below is the code in question  it can be run in a playground    import Cocoa  let url    https   api forecast io forecast apiKey 37 5673776 122 048951   if let url   NSURL string  url        if let data   try  Data contentsOf  url as URL            do               let parsedData   try JSONSerialization jsonObject with  data as Data  options   allowFragments             Store response in NSDictionary for easy access         let dict   parsedData as  NSDictionary          let currentConditions      dict   currently                 This produces an error  Type  Any  has no subscript members         let currentTemperatureF       dict   currently     temperature       as NSString  doubleValue                Display all current conditions from API             print currentConditions                 Output the current temperature in Fahrenheit             print currentTemperatureF                       else throw an error detailing what went wrong         catch let error as NSError               print  Details of JSON parsing error  n   error                        Edit  Here is a sample of the results from the API call after print currentConditions     icon   partly-cloudy-night   precipProbability   0   pressure   1015 39   humidity   0 75   precipIntensity   0   windSpeed   6 04   summary   Partly Cloudy   ozone   321 13   temperature   49 45   dewPoint   41 75   apparentTemperature   47   windBearing   332   cloudCover   0 28   time   1480846460

User · Answer

User                     FirstUser             name   John                     Information   XY            SecondUser             name   Tom                          If I create model using previous json Using this link  blog    http   www jsoncafe com to generate Codable structure or Any Format   Model  import Foundation struct RootClass   Codable       let user    Users       enum CodingKeys  String  CodingKey           case user    User             init from decoder  Decoder  throws           let values   try  decoder container keyedBy  CodingKeys self          user   try  values  decodeIfPresent  Users  self  forKey   user           struct Users   Codable       let firstUser   FirstUser      let information   String      let secondUser   SecondUser      enum CodingKeys  String  CodingKey           case firstUser    FirstUser          case information    Information          case secondUser    SecondUser            init from decoder  Decoder  throws           let values   try  decoder container keyedBy  CodingKeys self          firstUser   try  FirstUser from  decoder          information   try  values  decodeIfPresent String self  forKey   information          secondUser   try  SecondUser from  decoder          struct SecondUser   Codable       let name   String      enum CodingKeys  String  CodingKey           case name    name            init from decoder  Decoder  throws           let values   try  decoder container keyedBy  CodingKeys self          name   try  values  decodeIfPresent String self  forKey   name          struct FirstUser   Codable       let name   String      enum CodingKeys  String  CodingKey           case name    name            init from decoder  Decoder  throws           let values   try  decoder container keyedBy  CodingKeys self          name   try  values  decodeIfPresent String self  forKey   name            Parse      do           let res   try JSONDecoder   decode RootClass self  from  data          print res  user  first  firstUser  name     Yours optional value         catch           print error

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Swift has a powerful type inference  Lets get rid of  quot if let quot  or  quot guard let quot  boilerplate and force unwraps using functional approach   Here is our JSON  We can use optional JSON or usual  I m using optional in our example   let json  Dictionary lt String  Any gt       quot current quot     quot temperature quot   10     Helper functions  We need to write them only once and then reuse with any dictionary       Curry public func curry lt A  B  C gt    f   escaping  A  B  - gt  C  - gt   A  - gt   B  - gt  C       return   a in           f a   0                 Function that takes key and optional dictionary and returns optional value public func extract lt Key  Value gt    key  Key    json  Dictionary lt Key  Any gt    - gt  Value        return json flatMap           cast  0 key                Function that takes key and return function that takes optional dictionary and returns optional value public func extract lt Key  Value gt    key  Key  - gt   Dictionary lt Key  Any gt    - gt  Value        return curry extract  key         Precedence group for our operator precedencegroup RightApplyPrecedence       associativity  right     higherThan  AssignmentPrecedence     lowerThan  TernaryPrecedence        Apply  g    f    a     g f a   infix operator      RightApplyPrecedence public func    lt A  B gt    f   A  - gt  B    a  A  - gt  B       return f a         Wrapper around operator  quot as quot   public func cast lt A  B gt    a  A  - gt  B        return a as  B     And here is our magic - extract the value   let temperature    extract  quot temperature quot      extract  quot current quot      json     NSNotFound  Just one line of code and no force unwraps or manual type casting  This code works in playground  so you can copy and check it  Here is an implementation on GitHub

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Swift 5 Cant fetch data from your api  Easiest way to parse json is Use Decodable protocol  Or Codable  Encodable  amp  Decodable   For ex  let json    quot  quot  quot         quot dueDate quot              quot year quot   2021           quot month quot   2           quot day quot   17          quot  quot  quot   struct WrapperModel  Codable       var dueDate  DueDate    struct DueDate  Codable       var year  Int     var month  Int     var day  Int    let jsonData   Data json utf8   let decoder   JSONDecoder    do       let model   try decoder decode WrapperModel self  from  jsonData      print model    catch       print error localizedDescription

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This is an other way to solve your problem  So please check out below solution  Hope it will help you   let str       names       Bob      Tim      Tina      let data   str data using  String Encoding utf8  allowLossyConversion  false   do       let json   try JSONSerialization jsonObject with  data  options      as   String  AnyObject      if let names   json  names   as   String            print names          catch let error as NSError       print  Failed to load    error localizedDescription

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let str       names       Bob      Tim      Tina       let data   str data using  String Encoding utf8  allowLossyConversion  false    do       let json   try JSONSerialization jsonObject with  data  options      as   String  AnyObject      if let names   json  names   as   String             print names      catch let error as NSError       print  Failed to load    error localizedDescription

User · Answer

The problem is with the API interaction method  The JSON parsing is changed only in syntax  The main problem is with the way of fetching data  What you are using is a synchronous way of getting data  This doesn t work in every case  What you should be using is an asynchronous way to fetch data  In this way  you have to request data through the API and wait for it to respond with data  You can achieve this with URL session and third party libraries like Alamofire  Below is the code for URL Session method   let urlString    https   api forecast io forecast apiKey 37 5673776 122 048951  let url   URL init string  urlString  URLSession shared dataTask with url      data  response  error  in     guard error    nil else           print error            do           let Data   try JSONSerialization jsonObject with  data   as   String Any             Note if your data is coming in Array you should be using  Any              Now your data is parsed in Data variable and you can use it normally         let currentConditions   Data  currently   as   String Any          print currentConditions          let currentTemperatureF   currentConditions  temperature   as  Double         print currentTemperatureF        catch let error as NSError           print error          resume

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A big change that happened with Xcode 8 Beta 6 for Swift 3 was that id now imports as Any rather than AnyObject   This means that parsedData is returned as a dictionary of most likely with the type  Any Any   Without using a debugger I could not tell you exactly what your cast to NSDictionary will do but the error you are seeing is because dict   currently    has type Any  So  how do you solve this  From the way you ve referenced it  I assume dict   currently    is a dictionary and so you have many options   First you could do something like this     let currentConditionsDictionary   String  AnyObject    dict   currently    as   String  AnyObject      This will give you a dictionary object that you can then query for values and so you can get your temperature like this     let currentTemperatureF   currentConditionsDictionary  temperature   as  Double   Or if you would prefer you can do it in line     let currentTemperatureF    dict   currently    as   String  AnyObject    temperature    as  Double   Hopefully this helps  I m afraid I have not had time to write a sample app to test it   One final note  the easiest thing to do  might be to simply cast the JSON payload into  String  AnyObject  right at the start   let parsedData   try JSONSerialization jsonObject with  data as Data  options   allowFragments  as  Dictionary lt String  AnyObject gt

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I built quicktype exactly for this purpose  Just paste your sample JSON and quicktype generates this type hierarchy for your API data   struct Forecast       let hourly  Hourly     let daily  Daily     let currently  Currently     let flags  Flags     let longitude  Double     let latitude  Double     let offset  Int     let timezone  String    struct Hourly       let icon  String     let data   Currently      let summary  String    struct Daily       let icon  String     let data   Datum      let summary  String    struct Datum       let precipIntensityMax  Double     let apparentTemperatureMinTime  Int     let apparentTemperatureLowTime  Int     let apparentTemperatureHighTime  Int     let apparentTemperatureHigh  Double     let apparentTemperatureLow  Double     let apparentTemperatureMaxTime  Int     let apparentTemperatureMax  Double     let apparentTemperatureMin  Double     let icon  String     let dewPoint  Double     let cloudCover  Double     let humidity  Double     let ozone  Double     let moonPhase  Double     let precipIntensity  Double     let temperatureHigh  Double     let pressure  Double     let precipProbability  Double     let precipIntensityMaxTime  Int     let precipType  String      let sunriseTime  Int     let summary  String     let sunsetTime  Int     let temperatureMax  Double     let time  Int     let temperatureLow  Double     let temperatureHighTime  Int     let temperatureLowTime  Int     let temperatureMin  Double     let temperatureMaxTime  Int     let temperatureMinTime  Int     let uvIndexTime  Int     let windGust  Double     let uvIndex  Int     let windBearing  Int     let windGustTime  Int     let windSpeed  Double    struct Currently       let precipProbability  Double     let humidity  Double     let cloudCover  Double     let apparentTemperature  Double     let dewPoint  Double     let ozone  Double     let icon  String     let precipIntensity  Double     let temperature  Double     let pressure  Double     let precipType  String      let summary  String     let uvIndex  Int     let windGust  Double     let time  Int     let windBearing  Int     let windSpeed  Double    struct Flags       let sources   String      let isdStations   String      let units  String     It also generates dependency-free marshaling code to coax the return value of JSONSerialization jsonObject into a Forecast  including a convenience constructor that takes a JSON string so you can quickly parse a strongly typed Forecast value and access its fields   let forecast   Forecast from json  jsonString   print forecast daily data 0  windGustTime    You can install quicktype from npm with npm i -g quicktype or use the web UI to get the complete generated code to paste into your playground

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Updated the isConnectToNetwork-Function afterwards  thanks to this post   I wrote an extra method for it    import SystemConfiguration  func loadingJSON   link String  postString String  completionHandler   escaping    JSONObject  AnyObject  - gt             if isConnectedToNetwork      false           completionHandler  -1  as AnyObject          return            let request   NSMutableURLRequest url  URL string  link        request httpMethod    POST      request httpBody   postString data using  String Encoding utf8       let task   URLSession shared dataTask with  request as URLRequest    data  response  error in         guard error    nil  amp  amp  data    nil else      check for fundamental networking error             print  error   error                return                    if let httpStatus   response as  HTTPURLResponse   httpStatus statusCode    200      check for http errors             print  statusCode should be 200  but is   httpStatus statusCode                print  response     response                        JSON successfull         do               let parseJSON   try JSONSerialization jsonObject with  data   options   allowFragments              DispatchQueue main async execute                    completionHandler parseJSON as AnyObject                            catch let error as NSError               print  Failed to load    error localizedDescription                        task resume      func isConnectedToNetwork   - gt  Bool        var zeroAddress   sockaddr in sin len  0  sin family  0  sin port  0  sin addr  in addr s addr  0   sin zero   0  0  0  0  0  0  0  0       zeroAddress sin len   UInt8 MemoryLayout size ofValue  zeroAddress       zeroAddress sin family   sa family t AF INET       let defaultRouteReachability   withUnsafePointer to   amp zeroAddress             0 withMemoryRebound to  sockaddr self  capacity  1   zeroSockAddress in             SCNetworkReachabilityCreateWithAddress nil  zeroSockAddress                       var flags  SCNetworkReachabilityFlags   SCNetworkReachabilityFlags rawValue  0      if SCNetworkReachabilityGetFlags defaultRouteReachability    amp flags     false           return false            let isReachable    flags rawValue  amp  UInt32 kSCNetworkFlagsReachable      0     let needsConnection    flags rawValue  amp  UInt32 kSCNetworkFlagsConnectionRequired      0     let ret    isReachable  amp  amp   needsConnection       return ret     So now you can easily call this in your app wherever you want  loadingJSON  yourDomain com login php   postString  email   userEmail   amp password   password       parseJSON in      if String describing  parseJSON      -1            print  No Internet         else        if let loginSuccessfull   parseJSON  loginSuccessfull   as  Bool                 do stuff

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First of all never load data synchronously from a remote URL  use always asynchronous methods like URLSession       Any  has no subscript members   occurs because the compiler has no idea of what type the intermediate objects are  for example currently in   currently     temperature    and since you are using Foundation collection types like NSDictionary the compiler has no idea at all about the type   Additionally in Swift 3 it s required to inform the compiler about the type of all subscripted objects   You have to cast the result of the JSON serialization to the actual type   This code uses URLSession and exclusively Swift native types  let urlString    https   api forecast io forecast apiKey 37 5673776 122 048951   let url   URL string  urlString  URLSession shared dataTask with url      data  response  error  in   if error    nil       print error      else       do          let parsedData   try JSONSerialization jsonObject with  data   as   String Any        let currentConditions   parsedData  currently   as   String Any         print currentConditions         let currentTemperatureF   currentConditions  temperature   as  Double       print currentTemperatureF        catch let error as NSError         print error               resume     To print all key   value pairs of currentConditions you could write   let currentConditions   parsedData  currently   as   String Any     for  key  value  in currentConditions       print    key  -   value           A note regarding jsonObject with data   Many  it seems all  tutorials suggest  mutableContainers or  mutableLeaves options which is completely nonsense in Swift  The two options are legacy Objective-C options to assign the result to NSMutable    objects  In Swift any variable is mutable by default and passing any of those options and assigning the result to a let constant has no effect at all  Further most of the implementations are never mutating the deserialized JSON anyway   The only  rare  option which is useful in Swift is  allowFragments which is required if if the JSON root object could be a value type String  Number  Bool or null  rather than one of the collection types  array or dictionary   But normally omit the options parameter which means No options                                                                                Some general considerations to parse JSON  JSON is a well-arranged text format  It s very easy to read a JSON string  Read the string carefully  There are only six different types      two collection types and four value types     The collection types are   Array - JSON  objects in square brackets    - Swift   Any  but in most cases   String Any   Dictionary - JSON  objects in curly braces    - Swift   String Any    The value types are   String - JSON  any value in double quotes  Foo   even  123 or  false      Swift  String Number - JSON  numeric values not in double quotes 123 or 123 0     Swift  Int or Double Bool - JSON  true or false not in double quotes     Swift  true or false null - JSON  null     Swift  NSNull   According to the JSON specification all keys in dictionaries are required to be String      Basically it s always recommeded to use optional bindings to unwrap optionals safely  If the root object is a dictionary      cast the type to  String Any   if let parsedData   try JSONSerialization jsonObject with  data   as   String Any          and retrieve values by keys with  OneOfSupportedJSONTypes is either JSON collection or value type as described above    if let foo   parsedData  foo   as  OneOfSupportedJSONTypes       print foo         If the root object is an array      cast the type to   String Any    if let parsedData   try JSONSerialization jsonObject with  data   as    String Any           and iterate through the array with   for item in parsedData       print item      If you need an item at specific index check also if the index exists  if let parsedData   try JSONSerialization jsonObject with  data   as    String Any    parsedData count  gt  2     let item   parsedData 2  as  OneOfSupportedJSONTypes         print item              In the rare case that the JSON is simply one of the value types      rather than a collection type     you have to pass the  allowFragments option and cast the result to the appropriate value type for example   if let parsedData   try JSONSerialization jsonObject with  data   options   allowFragments  as  String         Apple has published a comprehensive article in the Swift Blog  Working with JSON in Swift                                                                                 In Swift 4  the Codable protocol provides a more convenient way to parse JSON directly into structs   classes   For example the given JSON sample in the question  slightly modified   let jsonString         icon    partly-cloudy-night    precipProbability   0   pressure   1015 39   humidity   0 75   precip intensity   0   wind speed   6 04   summary    Partly Cloudy    ozone   321 13   temperature   49 45   dew point   41 75   apparent temperature   47   wind bearing   332   cloud cover   0 28   time   1480846460        can be decoded into the struct Weather  The Swift types are the same as described above  There are a few additional options    Strings representing an URL can be decoded directly as URL   The time integer can be decoded as Date with the dateDecodingStrategy  secondsSince1970  snaked cased JSON keys can be converted to camelCase with the keyDecodingStrategy  convertFromSnakeCase     struct Weather  Decodable       let icon  summary  String     let pressure  Double  humidity  windSpeed   Double     let ozone  temperature  dewPoint  cloudCover  Double     let precipProbability  precipIntensity  apparentTemperature  windBearing   Int     let time  Date    let data   Data jsonString utf8  do       let decoder   JSONDecoder       decoder dateDecodingStrategy    secondsSince1970     decoder keyDecodingStrategy    convertFromSnakeCase     let result   try decoder decode Weather self  from  data      print result    catch       print error      Other Codable sources    Apple  Encoding and Decoding Custom Types HackingWithSwift  Codable Cheat Sheet Ray Wenderlich  Encoding and Decoding in Swift

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