JSON parsing in Swift 4 with complex & nested data - json

Question

I am currently trying to make a weather app using JSON from https://openweathermap.org but I am having trouble with the weather part in the JSON file. I am not sure how to access the 'id' value inside the object.
{
"base": "stations",
"clouds": {
"all": 36
},
"cod": 200,
"coord": {
"lat": 51.51,
"lon":
-0.13
},
"dt": 1507497600,
"id": 2643743,
"main": {
"humidity": 82,
"pressure": 1021,
"temp": 10.65,
"temp_max": 13,
"temp_min": 9
},
"name": "London",
"sys": {
"country": "GB",
"id": 5091,
"message": 0.0036,
"sunrise": 1507443264,
"sunset": 1507483213,
"type": 1
},
"visibility": 10000,
"weather": [{
"description": "scattered clouds",
"icon": "03n",
"id": 802,
"main": "Clouds"
}],
"wind": {
"deg": 200,
"speed": 1.5
}
}
How would I be able to get the data in there. In my swift code, I am using structures that conform to the new 'codable' protocol in swift 4.
// all structures for the data
struct CurrentLocalWeather: Codable {
let base: String
let clouds: clouds
let cod: Int
let coord: coord
let dt: Int
let id: Int
let main: main
let name: String
let sys: sys
let visibility: Int
let weather: [weather]
let wind: wind
}
struct clouds: Codable {
let all: Int
}
struct coord: Codable {
let lat: Double
let lon: Double
}
struct main: Codable {
let humidity: Double
let pressure: Double
let temp: Double
let temp_max: Double
let temp_min: Double
}
struct sys: Codable {
let country: String
let id: Int
let message: Double
let sunrise: Double
let sunset: Double
let type: Int
}
struct weather: Codable {
let description: String
let icon: String
let id: Int
let main: String
}
struct wind: Codable {
let deg: Double
let speed: Double
}
// Get data from weather server
func getCurrentWeatherData() {
let jsonUrlString = "https://api.openweathermap.org/data/2.5/weather?id=2643743&units=metric&APPID=fdf04e9483817ae2fa77048f7e6705e8"
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 decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601
let json = try decoder.decode(CurrentLocalWeather.self, from: data)
print("Data Successfully Retrieved!\nServer Response: \(json.cod)\nLocation: \(json.name)")
DispatchQueue.main.async() {
// Any of the following allows me to access the data from the JSON
self.locationLabel.text = "\(json.name)"
self.temperatureLabel.text = "Currently: \(json.main.temp)ºC"
self.highTemperatureLabel.text = "High: \(json.main.temp_max)ºC"
self.lowTemperatureLabel.text = "Low: \(json.main.temp_min)ºC"
self.sunriseLabel.text = "\(self.convertFromUnixToNormal(time: json.sys.sunrise))"
self.sunsetLabel.text = "\(self.convertFromUnixToNormal(time: json.sys.sunset))"
self.humidityLabel.text = "Humidity: \(json.main.humidity)%"
self.pressureLabel.text = "Pressure: \(json.main.pressure) hPa"
self.windSpeedLabel.text = "Wind Speed: \(json.wind.speed) km/h"
}
} catch let jsonErr {
print("Error: \(jsonErr)")
}
}.resume()
}

Answer 1

You need to properly identify your json string and provide all necessary structures to decode it. Just by looking at the json provided you can have an idea of the necessary structs to decode it properly:
struct CurrentLocalWeather: Codable {
let base: String
let clouds: Clouds
let cod: Int
let coord: Coord
let dt: Int
let id: Int
let main: Main
let name: String
let sys: Sys
let visibility: Int
let weather: [Weather]
let wind: Wind
}
struct Clouds: Codable {
let all: Int
}
struct Coord: Codable {
let lat: Double
let lon: Double
}
struct Main: Codable {
let humidity: Int
let pressure: Int
let temp: Double
let tempMax: Int
let tempMin: Int
private enum CodingKeys: String, CodingKey {
case humidity, pressure, temp, tempMax = "temp_max", tempMin = "temp_min"
}
}
struct Sys: Codable {
let country: String
let id: Int
let message: Double
let sunrise: UInt64
let sunset: UInt64
let type: Int
}
struct Weather: Codable {
let description: String
let icon: String
let id: Int
let main: String
}
struct Wind: Codable {
let deg: Int
let speed: Double
}
let weatherData = Data("""
{"base" : "stations",
"clouds": { "all": 36 },
"cod" : 200,
"coord" : { "lat": 51.51,
"lon": -0.13},
"dt": 1507497600,
"id": 2643743,
"main": {
"humidity": 82,
"pressure": 1021,
"temp": 10.65,
"temp_max": 13,
"temp_min": 9},
"name": "London",
"sys": {
"country": "GB",
"id": 5091,
"message": 0.0036,
"sunrise": 1507443264,
"sunset": 1507483213,
"type": 1 },
"visibility": 10000,
"weather": [{
"description": "scattered clouds",
"icon": "03n",
"id": 802,
"main": "Clouds"}],
"wind": {
"deg": 200,
"speed": 1.5
}
}
""".utf8)
let decoder = JSONDecoder()
do {
let currentLocalWeather = try decoder.decode(CurrentLocalWeather.self, from: weatherData)
print(currentLocalWeather) // "CurrentLocalWeather(base: "stations", clouds: __lldb_expr_367.Clouds(all: 36), cod: 200, coord: __lldb_expr_367.Coord(lat: 51.509999999999998, lon: -0.13), dt: 1507497600, id: 2643743, main: __lldb_expr_367.Main(humidity: 82, pressure: 1021, temp: 10.65, temp_max: 13, temp_min: 9), name: "London", sys: __lldb_expr_367.Sys(country: "GB", id: 5091, message: 0.0035999999999999999, sunrise: 1507443264, sunset: 1507483213, type: 1), visibility: 10000, weather: [__lldb_expr_367.Weather(description: "scattered clouds", icon: "03n", id: 802, main: "Clouds")], wind: __lldb_expr_367.Wind(deg: 200, speed: 1.5))\n"
} catch {
print(error)
}

Answer 2

You need to define types for the custom types in your JSON, e.g. weather, clouds, coord, etc. I would recommend looking at the example in the documentation.
In the example, the Landmark type has a 'location' property which is of Coordinate type. You could even use the Coordinate type in the example for the coord property in your JSON object. However, you will need to provide the correct keys using the CodingKey protocol which is also described in the documentation. For example, your Coordinate type may look like this:
struct Coordinate: Codable {
var latitude: Double
var longitude: Double
enum CodingKeys: String, CodingKey {
case latitude = "lat"
case longitude = "lon"
}
}