问题
I have been trying to get this code to work for like 6 hours. I get the error: "failed to convert The data couldn’t be read because it is missing." I don't know while the File is missing is there something wrong in my models(structs). Do I need to write a struct for very json dictionary? Currently I have only made those JSON dictionaries to a struct, which I actually need. The full JSON file can be found at https://api.met.no/weatherapi/sunrise/2.0/.json?lat=40.7127&lon=-74.0059&date=2020-12-22&offset=-05:00 . I want to be able to print the time of the sunrise, sunset and solar noon as well as the elevation of the sun at solar noon. It's currently 1 am and I am desperate. Good Night!
class ViewController: NSViewController {
@IBOutlet weak var sunriseField: NSTextField!
@IBOutlet weak var sunsetField: NSTextField!
@IBOutlet weak var daylengthField: NSTextField!
override func viewDidLoad() {
super.viewDidLoad()
let url = "https://api.met.no/weatherapi/sunrise/2.0/.json?lat=40.7127&lon=-74.0059&date=2020-12-22&offset=-05:00"
getData(from: url)
// Do any additional setup after loading the view.
}
private func getData(from url: String) {
let task = URLSession.shared.dataTask(with: URL(string: url)!, completionHandler: {data, response, error in
guard let data = data, error == nil else {
print("something went wrong")
return
}
var result: MyTime?
do {
result = try JSONDecoder().decode(MyTime.self, from: data)
}
catch {
print("failed to convert \(error.localizedDescription)")
}
guard let json = result else {
return
}
let sunrise1 = json.sunrise.time
DispatchQueue.main.async { [weak self] in
self?.sunriseField.stringValue = sunrise1
}
print(json)
})
task.resume()
}
override var representedObject: Any? {
didSet {
// Update the view, if already loaded.
}
}
}
struct MyData : Codable {
let location : Location
let meta : Meta
}
struct MyTime : Codable {
let solarnoon : Solarnoon
let sunset : Sunset
let sunrise : Sunrise
}
struct Location : Codable {
let height : String
let time : [MyTime]
let longitude : String
let latitude : String
}
struct Meta : Codable {
let licenseurl : String
}
struct Solarnoon : Codable {
let desc : String
let time : String
let elevation : String
}
struct Sunrise : Codable {
let desc : String
let time : String
}
struct Sunset : Codable {
let time : String
let desc : String
}
回答1:
You don't really have a SwiftUI class, but that is a different question. I am going to work on fixing getData(). I have tried to comment it extensively, but let me know if you have any questions.
private func getData(from url: String) {
// Personally I like converting the string to a URL to unwrap it and make sure it is valid:
guard let url = URL(string: urlString) else {
print("Bad URL: \(urlString)")
return
}
let config = URLSessionConfiguration.default
// This will hold the request until you have internet
config.waitsForConnectivity = true
URLSession.shared.dataTask(with: url) { data, response, error in
// A check for a bad response
guard let httpResponse = response as? HTTPURLResponse,
httpResponse.statusCode == 200 else {
print("Bad Server Response")
return
}
if let data = data {
// You can print(data) here that will shown you the number of bytes returned for debugging.
//This work needs to be done on the main thread:
DispatchQueue.main.async {
let decoder = JSONDecoder()
if let json = try? decoder.decode(MetDecoder.self, from: data){
print(json)
//At this point, you have your data in a struct
self.sunriseTime = json.dailyData?.solarData?.first?.sunrise?.time
}
}
}
}
.resume()
}
With regard to your structs, you only need them for the data you are trying to parse. If you don't need it, don't worry about it. I would make this a separate class named MetDecoder or something that makes sense to you and indicates the decoder for your JSON. You will also note that I changed the names of some of the variables. You can do that so long as you use a CodingKeys enum to translate your JSON to your struct as in the case of dailyData = "location", etc. This is ugly JSON, and I am not sure why the Met decided everything should be a string, but this decoder is tested and it works:
import Foundation
// MARK: - MetDecoder
struct MetDecoder: Codable {
let dailyData: DailyData?
enum CodingKeys: String, CodingKey {
case dailyData = "location"
}
}
// MARK: - Location
struct DailyData: Codable {
let solarData: [SolarData]?
enum CodingKeys: String, CodingKey {
case solarData = "time"
}
}
// MARK: - Time
struct SolarData: Codable {
let sunrise, sunset: RiseSet?
let solarnoon: Position?
let date: String?
enum CodingKeys: String, CodingKey {
case sunrise, sunset, solarnoon, date
}
}
// MARK: - HighMoon
struct Position: Codable {
let time: String?
let desc, elevation, azimuth: String?
}
// MARK: - Moonrise
struct RiseSet: Codable {
let time: String?
let desc: String?
}
You should see what the National Weather Service does to us in the US to get the JSON. Lastly, when working on JSON I find the following pages VERY helpful: JSON Formatter & Validator which will help you parse out the wall of text that gets returned in a browser, and quicktype which will parse JSON into a programming language like Swift. I will warn you that the parsing can give some very ugly structs in Swift, but it gives you a nice start. I used both sites for this answer.
回答2:
Apple's new framework, Combine, helps to simplify the code needed for async fetch requests. I have used the MetDecoder in @Yrb's response above (you can accept his answer) and altered the getData() function. Just make sure you import Combine at the top.
import Combine
var sunriseTime: String?
var sunsetTime: String?
var solarNoonTime: String?
var solarNoonElevation: String?
func getData() {
let url = URL(string: "https://api.met.no/weatherapi/sunrise/2.0/.json?lat=40.7127&lon=-74.0059&date=2020-12-22&offset=-05:00")!
URLSession.shared.dataTaskPublisher(for: url)
// fetch on background thread
.subscribe(on: DispatchQueue.global(qos: .background))
// recieve response on main thread
.receive(on: DispatchQueue.main)
// ensure there is data
.tryMap { (data, response) in
guard
let httpResponse = response as? HTTPURLResponse,
httpResponse.statusCode == 200 else {
throw URLError(.badServerResponse)
}
return data
}
// decode JSON data to MetDecoder
.decode(type: MetDecoder.self, decoder: JSONDecoder())
// Handle results
.sink { (result) in
// will return success or failure
print("completion: \(result)")
} receiveValue: { (value) in
// if success, will return MetDecoder
// here you can update your view
print("value: \(value)")
if let solarData = value.dailyData?.solarData?.first {
self.sunriseTime = solarData.sunrise?.time
self.sunsetTime = solarData.sunset?.time
self.solarNoonTime = solarData.solarnoon?.time
self.solarNoonElevation = solarData.solarnoon?.elevation
}
}
// After recieving response, the URLSession is no longer needed & we can cancel the publisher
.cancel()
}
回答3:
from the json data (2nd entry), looks like you need at least:
struct MyTime : Codable {
let solarnoon : Solarnoon?
let sunset : Sunset?
let sunrise : Sunrise?
}
and you need:
var result: MyData?
do {
result = try JSONDecoder().decode(MyData.self, from: data)
}
catch {
print("----> error failed to convert \(error)")
}
来源：https://stackoverflow.com/questions/65417381/json-file-is-missing-struct-is-wrong