currently working through an app that gets and decodes data from OpenWeatherMap API, currently I've got everything working except getting the decoder to return something. Currently, the decoder is returning nil, however, I am getting bytes of data from the API call. I am not exactly sure what could be the issue. I've got the ViewModel struct set up in terms of hierarchy. The OPW API JSON data seems to be in the format of a dictionary key:value pair collection type, keys are enclosed in quotes, could it be that my decoder isn't finding the necessary information because of the quotation marks?
Getting and Decoding the API call...
#IBAction func saveCityButtonPressed() {
if let city = cityNameTextField.text {
let weatherURL = URL(string: "https://api.openweathermap.org/data/2.5/weather?q=\(city)&APPID=8bad8461edbaf3ff50aa2f2fd8ad8a71&units=imperial")!
let weatherResource = Resource<WeatherViewModel>(url: weatherURL) { data in
let weatherVM = try? JSONDecoder().decode(WeatherViewModel.self, from: data)
return weatherVM
}
Webservice().load(resource: weatherResource) { result in
}
}
}
ViewModel
struct WeatherListViewModel {
private var weatherViewModels = [WeatherViewModel]()
}
struct WeatherViewModel: Decodable {
let name: String
let main: TemperatureViewModel
}
struct TemperatureViewModel: Decodable {
let temp: Double
let temp_min: Double
let temp_max: Double
}
Example of JSON data:
{
"coord":{
"lon":-0.13,
"lat":51.51
},
"weather":[
{
"id":300,
"main":"Drizzle",
"description":"light intensity drizzle","icon":"09d"
}
],
"base":"stations",
"main":{
"temp":280.32,
"pressure":1012,
"humidity":81,
"temp_min":279.15,
"temp_max":281.15
},
"visibility":10000,
"wind":{
"speed":4.1,
"deg":80
},
"clouds":{
"all":90
},
"dt":1485789600,
"sys":{
"type":1,
"id":5091,
"message":0.0103,
"country":"GB",
"sunrise":1485762037,
"sunset":1485794875
},
"id":2643743,
"name":"London",
"cod":200
}
By making the result of JSONDecoder().decode an optional (try?), you are ensuring that you get nil if the decoding goes wrong. You can catch decoding related issues quickly by implementing proper catch blocks. E.g.:
do {
let decoder = JSONDecoder()
let messages = try decoder.decode(WeatherViewModel.self, from: data)
print(messages as Any)
} catch DecodingError.dataCorrupted(let context) {
print(context)
} catch DecodingError.keyNotFound(let key, let context) {
print("Key '\(key)' not found:", context.debugDescription)
print("codingPath:", context.codingPath)
} catch DecodingError.valueNotFound(let value, let context) {
print("Value '\(value)' not found:", context.debugDescription)
print("codingPath:", context.codingPath)
} catch DecodingError.typeMismatch(let type, let context) {
print("Type '\(type)' mismatch:", context.debugDescription)
print("codingPath:", context.codingPath)
} catch {
print("error: ", error)
}
Not a direct answer to your question, but surely will reduce other's time to understand which part of decoding is going wrong.
Your WeatherViewModel property city is a String, but there is no "city" key in your JSON.
Why do we get nil value, when decoding the value?
Reasons:
The response parameter may be the first letter as capital.
Solution:
The coding keys concept is to out to nil value.
Example:
struct Example{
var a: string
var b: string
enum Codingkeys: String,CodingKey{
case a = "a"
case b = "b"
}
}
Related
This question already has an answer here:
Swift 4 JSON Codable - value returned is sometimes an object, others an array
(1 answer)
Closed 3 years ago.
Let's say I have an array of JSON response from the GET method like :
[{
"id":"1",
"Name":"John Doe",
},{
"id":"2",
"Name":"Jane Doe",
}]
And from the POST method using id param I only have 1 object JSON response :
{
"id":"1",
"Name":"John Doe",
}
how can I write a method to decode both the JSON dynamically?
At the moment, this is what I'm using :
func convertJSON<T:Decodable>(result: Any?, model: T.Type) -> T? {
if let res = result {
do {
let data = try JSONSerialization.data(withJSONObject: res, options: JSONSerialization.WritingOptions.prettyPrinted)
return try JSONDecoder().decode(model, from: data)
} catch {
print(error)
return nil
}
} else {
return nil
}
}
The method can be used to decode a single object using dynamic model, but I just can't figure it out to handle a single object / an array of objects dynamically.
The most I can get with is just using a duplicate of the method but replacing T with
[T] in the method parameter and return type, if the response is an array.
I'm open to any suggestion, any help is appreciated, Thank You in advance.
Edit : If this question is duplicate of this , I'm not sure how the marked answer could be a solution.
One solution could be to always return [Model]?.
Inside your function first try to decode as Model, on success return an array with that single decoded object inside it. If this fails then try to decode as [Model], on success return the decoded object else return nil.
Using your sample JSONs I created a struct:
struct Person: Codable {
let id, name: String
enum CodingKeys: String, CodingKey {
case id
case name = "Name"
}
}
Then I created a struct with a couple of methods to decode from either a String or an optional Data.
struct Json2Type<T: Decodable> {
// From data to type T
static public func convertJson(_ data: Data?) -> [T]? {
// Check data is not nil
guard let data = data else { return nil }
let decoder = JSONDecoder()
// First try to decode as a single object
if let singleObject = try? decoder.decode(T.self, from: data) {
// On success return the single object inside an array
return [singleObject]
}
// Try to decode as multiple objects
guard let multipleObjects = try? decoder.decode([T].self, from: data) else { return nil }
return multipleObjects
}
// Another function to decode from String
static public func convertJson(_ string: String) -> [T]? {
return convertJson(string.data(using: .utf8))
}
}
Finally call the method you prefer:
Json2Type<Person>.convertJson(JsonAsDataOrString)
Update: #odin_123, a way to have either a Model or [Model] as return value can be accomplish using an enum. We can even add the error condition there to avoid returning optionals. Let's define the enum as:
enum SingleMulipleResult<T> {
case single(T)
case multiple([T])
case error
}
Then the struct changes to something like this:
struct Json2Type<T: Decodable> {
static public func convertJson(_ data: Data?) -> SingleMulipleResult<T> {
guard let data = data else { return .error }
let decoder = JSONDecoder()
if let singleObject = try? decoder.decode(T.self, from: data) {
return .single(singleObject)
}
guard let multipleObjects = try? decoder.decode([T].self, from: data) else { return .error }
return .multiple(multipleObjects)
}
static public func convertJson(_ string: String) -> SingleMulipleResult<T> {
return convertJson(string.data(using: .utf8))
}
}
You can call it the same way we did before:
let response = Json2Type<Person>.convertJson(JsonAsDataOrString)
And use a switch to check every possible response value:
switch(response) {
case .single(let object):
print("One value: \(object)")
case .multiple(let objects):
print("Multiple values: \(objects)")
case .error:
print("Error!!!!")
}
I have reduced my dictionary keys successfully in this question as pseudo-code without a real json model. The goal which I accomplished in the previous question is to return only the keys that have matching values. So the output is a dictionary that looks something like this ["WoW": ["#jade", "#kalel"]. Exactly what I needed. Of course there could be other matches and I'd like to return those as well.
Now that I have a proper json model, the reduce function is printing out an empty dictionary [:]. Is it the type in .reduce(into: [String:[String]]() that is causing the issue?
All the data is printing so the json and model structure must be correct.
json
[
{
"id": "tokenID-tqkif48",
"name": "#jade",
"game": "WoW",
"age": "18"
},
{
"id": "tokenID-fvkif21",
"name": "#kalel",
"game": "WoW",
"age": "20"
}
]
UserModel
public typealias Users = [UserModel]
public struct UserModel: Codable {
public let name: String
public let game: String
// etc...
enum CodingKeys: String, CodingKey {
case name
case game
// etc...
Playground
guard let url = Bundle.main.url(forResource: "Users", withExtension: "json") else {
fatalError()
}
guard let data = try? Data(contentsOf: url) else {
fatalError()
}
let decoder = JSONDecoder()
do {
let response = try decoder.decode([UserModel].self, from: data)
for userModel in response {
let userDict: [String:String] = [ userModel.name:userModel.game ]
let reduction = Dictionary(grouping: userDict.keys) { userDict[$0] ?? "" }.reduce(into: [String:[String]](), { (result, element) in
if element.value.count > 1 {
result[element.key] = element.value
}
})
// error catch etc
}
Your code is too complicated. You can group the array by game simply with
let response = try decoder.decode([UserModel].self, from: data)
let reduction = Dictionary(grouping: response, by: {$0.game}).mapValues{ usermodel in usermodel.map{ $0.name}}
UPDATE I may be mistaking what you want to get. There's another code below and please check the results and choose one you want.
If you want to use reduce(into:updateAccumulatingResult:), you can write something like this.
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(name: String, game: String)] = response.map {($0.name, $0.game)}
let reduction = userArray.reduce(into: [String:[String]]()) {result, element in
if !element.game.isEmpty {
result[element.name, default: []].append(element.game)
}
}
print(reduction)
} catch {
print(error)
}
If you prefer an initializer of Dictionary, this may work:
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(name: String, games: [String])] = response.map {
($0.name, $0.game.isEmpty ? [] : [$0.game])
}
let reduction = Dictionary(userArray) {old, new in old + new}
print(reduction)
} catch {
print(error)
}
Both output:
["#jade": ["WoW"], "#kalel": ["WoW"]]
Anyway, your way of combining loop, Dictionary(grouping:) and reduce(into:) in addition of userDict.keys is making things too complex than they should be.
ADDITION When you want to get a Dictionary with keys as games:
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(game: String, name: String)] = response.compactMap {
$0.game.isEmpty ? nil : ($0.game, $0.name)
}
let reduction = userArray.reduce(into: [String:[String]]()) {result, element in
result[element.game, default: []].append(element.name)
}
print(reduction)
} catch {
print(error)
}
Or:
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(game: String, names: [String])] = response.compactMap {
$0.game.isEmpty ? nil : ($0.game, [$0.name])
}
let reduction = Dictionary(userArray) {old, new in old + new}
print(reduction)
} catch {
print(error)
}
Output:
["WoW": ["#jade", "#kalel"]]
I am new to swift programming and Xcode and am try to call mysql data from the database to Xcode using Json encoding. I was able to successfully call all the data (array) but when I decide to call only one value(column) say Courses.name I get the "Decoding Error -- Expected to decode Dictionary but found an array instead." How do I work my way around this problem? My goal is to print only courses.name
import UIKit
struct Course: Decodable {
let id: String
let name: String
let member: String
}
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let jsonUrlString = "http://oriri.ng/aapl/service.php"
guard let url = URL(string: jsonUrlString) else
{ return }
URLSession.shared.dataTask(with: url) { (data, response, err) in
guard let data = data else{ return }
do {
let courses = try JSONDecoder().decode(Course.self, from: data)
print(courses.name)
} catch let jsonErr {
print("Error serializing json:", jsonErr)
}
}.resume()
}
}
[{"id":"1","name":"sobande_ibukun","member":"blue"}]
The [] around denotes that it is an array. Decode with the following and it should work:
let courses = try JSONDecoder().decode([Course].self, from: data)
If you are sure that it will always be one course you can do:
print(courses.first!.name)
If there may be many courses you can print every name:
courses.forEach { course in print(course.name) }
Just wanted to add to Fabians response above.
The fix for showing all of them is to have a struct with each of your keys (in the array) like so:
struct Advisor_Info: Decodable {
let advisor_email: String
let advisor_firstname: String
let advisor_lastname: String
let advisor_phonenumber: String
}
Then extract your items from the JSON dictionary string like so:
do {
let decodedResponse = try JSONDecoder().decode([Advisor_Info].self, from: data)
print(decodedResponse as Any)
for each in decodedResponse {
print(each)
print(each.advisor_email)
}
} catch DecodingError.dataCorrupted(let context) {
print(context)
} catch DecodingError.keyNotFound(let key, let context) {
print("Key '\(key)' not found:", context.debugDescription)
print("codingPath:", context.codingPath)
} catch DecodingError.valueNotFound(let value, let context) {
print("Value '\(value)' not found:", context.debugDescription)
print("codingPath:", context.codingPath)
} catch DecodingError.typeMismatch(let type, let context) {
print("Type '\(type)' mismatch:", context.debugDescription)
print("codingPath:", context.codingPath)
} catch {
print("error: ", error)
}
}
I receive from a post request, this JSON:
"clinic_info": {
"city": "Querétaro",
"state": "Querétaro",
"country": "México",
"phone": null,
"ext": null,
"coords": "20.6046089,-100.37826050000001",
"location": "Querétaro"
}
But when it is empty the JSON is:
"clinic_info": []
This produces an error: Expected to decode Dictionary but found an array instead.
This is happening because decoder want dictionary and your JSON is array
Need to check before decoding that JSON response is dictionary or Array and do decoding accordingly.
If you find Dictionary then do like this
let myData = try JSONDecoder().decode(YourModel.self, from: jsonData)
If you find Array then do like this
let myData = try JSONDecoder().decode([YourModel].self, from: jsonData)
You can do it using try, throw like that
import Foundation
struct ClinicData: Codable {
let clinicInfo: ClinicInfo?
enum CodingKeys: String, CodingKey {
case clinicInfo = "clinic_info"
}
}
struct ClinicInfo: Codable {
let city, state, country: String
let coords, location: String
}
// MARK: Convenience initializers
extension ClinicData {
init(data: Data) throws {
self = try JSONDecoder().decode(ClinicData.self, from: data)
}
init(_ json: String, using encoding: String.Encoding = .utf8) throws {
guard let data = json.data(using: encoding) else {
throw NSError(domain: "JSONDecoding", code: 0, userInfo: nil)
}
try self.init(data: data)
}
func jsonData() throws -> Data {
return try JSONEncoder().encode(self)
}
func jsonString(encoding: String.Encoding = .utf8) throws -> String? {
return String(data: try self.jsonData(), encoding: encoding)
}
}
**get clinicInfo**
if let clinicData = try? ClinicData.init(data: Data()), let clinicInfo =
clinicData.clinicInfo{
}
The service that provides those JSON responses replies with:
"clinic_info": { ... }
Where ... is a valid JSON object.
But when it is empty, you are saying it looks like this:
"clinic_info": []
Notice the [] that say this is an empty array of objects.
You might want to change the service response (if possible), since it looks inconsistent to me having it return an object when it has valid data, and an array when there is no valid data.
The error message you are getting is clear:
Expected to decode Dictionary but found an array instead.
It expected an object {}, but found an array [].
The Array class has a method for this.
Using typeof will always return "object".
The code below shows how to use the isArray() method in the Array class.
const obj = {
_array: [],
_object: {}
}
console.log(Array.isArray(obj._array)); // true
console.log(Array.isArray(obj._object)); // false
I have json data like this code below:
{
"all": [
{
"ModelId": 1,
"name": "ghe",
"width": 2
},
{
"ModelId": 2,
"name": "ban",
"width": 3
}]
}
I try to get the modelId and convert it to String but it's not working with my code:
let data = NSData(contentsOf: URL(string: url)!)
do {
if let data = data, let json = try JSONSerialization.jsonObject(with: data as Data) as? [String: Any], let models = json["all"] as? [[String:Any]] {
for model in models {
if let name = model["ModelId"] as? String {
_modelList.append(name)
}
}
}
completion(_modelList)
}catch {
print("error")
completion(nil)
}
How to fix this issue? Thanks.
I think ModelId is integer type. So, can you try to cast it to Integer
for model in models {
if let name = model["ModelId"] as? Int{
_modelList.append("\(name)")
}
}
Hope, it will help you.
if let as? is to unwrap, not type casting. So you unwrap first, then you cast it into string.
for model in models {
if let name = model["ModelId"] as? Int {
_modelList.append("\(name)")
}
}
Currently you are looking for a wrong key ,
for model in models {
if let name = model["ModelId"] as? NSNumber {
_modelList.append(name.stringValue)
}
}
As long as you are using JSONSerialization.jsonObject to parse your JSON you have very little control over the type the deserialiser will create, you basically let the parser decide. Sensible as it is it will create "some kind of " NSNumber of an Int type from a number without quotes. This can not be cast to a String, therefore your program will fail.
You can do different things in order to "fix" this problem, I would like to suggest the Codable protocol for JSON-parsing, but this specific problem can probably only be solved using a custom initialiser which looks kind of verbose as can be seen in this question.
If you just want to convert your NSNumber ModelId to a String you will have to create a new object (instead of trying to cast in vain). In your context this might simply be
if let name = String(model["ModelId"]) { ...
This is still not an elegant solution, however it will solve the problem at hand.
another approach is:
import Foundation
struct IntString: Codable
{
var value: String = "0"
init(from decoder: Decoder) throws
{
// get this instance json value
let container = try decoder.singleValueContainer()
do
{
// try to parse the value as int
value = try String(container.decode(Int.self))
}
catch
{
// if we failed parsing the value as int, try to parse it as a string
value = try container.decode(String.self)
}
}
func encode(to encoder: Encoder) throws
{
var container = encoder.singleValueContainer()
try container.encode(value)
}
}
my solution is to create a new struct that will be able to receive either a String or and Int and parse it as a string, this way in my code i can decide how to treat it, and when my server sends me sometimes an Int value and sometimes a json with that same key as a String value - the parser can parse it without failing
of course you can do it with any type (date / double / float / or even a full struct), and even insert it with some logic of your own (say get the string value of an enum based on the received value and use it as index or whatever)
so your code should look like this:
import Foundation
struct Models: Codable {
let all: [All]
}
struct All: Codable {
let modelID: IntString
let name: String
let width: IntString
enum CodingKeys: String, CodingKey {
case modelID = "ModelId"
case name = "name"
case width = "width"
}
}
parse json into the Models struct:
let receivedModel: Decodable = Bundle.main.decode(Models.self, from: jsonData!)
assuming you'r json decoder is:
import Foundation
extension Bundle
{
func decode<T: Decodable>(_ type: T.Type, from jsonData: Data, dateDecodingStrategy: JSONDecoder.DateDecodingStrategy = .deferredToDate, keyDecodingStrategy: JSONDecoder.KeyDecodingStrategy = .useDefaultKeys) -> T
{
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = dateDecodingStrategy
decoder.keyDecodingStrategy = keyDecodingStrategy
do
{
return try decoder.decode(T.self, from: jsonData)
}
catch DecodingError.keyNotFound(let key, let context)
{
fatalError("Failed to decode \(jsonData) from bundle due to missing key '\(key.stringValue)' not found – \(context.debugDescription)")
}
catch DecodingError.typeMismatch(let type, let context)
{
print("Failed to parse type: \(type) due to type mismatch – \(context.debugDescription) the received JSON: \(String(decoding: jsonData, as: UTF8.self))")
fatalError("Failed to decode \(jsonData) from bundle due to type mismatch – \(context.debugDescription)")
}
catch DecodingError.valueNotFound(let type, let context)
{
fatalError("Failed to decode \(jsonData) from bundle due to missing \(type) value – \(context.debugDescription)")
}
catch DecodingError.dataCorrupted(_)
{
fatalError("Failed to decode \(jsonData) from bundle because it appears to be invalid JSON")
}
catch
{
fatalError("Failed to decode \(jsonData) from bundle: \(error.localizedDescription)")
}
}
}