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Day 49 Recieving Codable Data Issue...

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For some reason I am only getting an Unknown error message when running this code. I have tried debugging and it appears I am getting back data but decoding is apparently failing and I have no idea why. If anyone can help I would appreciate...

import SwiftUI

struct Response: Codable {
    var results: [Result]

struct Result: Codable {
    var trackID: Int
    var trackName: String
    var collectionName: String

struct SendingRecievingCodableDataSample: View {

    @State var results = [Result]()

    var body: some View {
        List(results, id: \.trackID) { item in
            VStack(alignment: .leading) {
//                Text(item.collectionName)
        }//: LIST
        .onAppear(perform: loadData)

    func loadData() {

     //: 1. Create URL we want to access

        guard let url = URL(string: "") else {
            print("Invalid URL")
        //: 2. Wrap that in a URLRequest

        let request = URLRequest(url: url)

        //: 3. Create and start networking task
        URLSession.shared.dataTask(with: request) { data, response, error in

            if let data = data {
                print("Data: \(data)")
                //: 4. Handle result of netwoking task
                if let decodedResponse = try? JSONDecoder().decode(Response.self, from: data) {
                    // we have good data – go back to the main thread
                    print ("DecodeResponse: \(decodedResponse)")

                    DispatchQueue.main.async {
                        // update our UI
                        self.results = decodedResponse.results
                        print ("Results: \(results)")


                    // everything is good, so we can exit

            // if we're still here it means there was a problem
            print("Fetch failed: \(error?.localizedDescription ?? "Unknown error")")




Your keys are not correct. You have trackID but the JSON response has trackId. You either need to rename the key in your Result struct or use a CodingKeys enum to map the key names.


Oh, and a (hopefully helpful) hint when decoding JSON:

Don't do this:

if let decodedResponse = try? JSONDecoder().decode(Response.self, from: data) {

because converting the return value of decode into an Optional masks any error that may occur.

Do this instead:

do {
    let decodedResponse = try JSONDecoder().decode(Response.self, from: data)
catch {

Once you get it working, you can go back to the other way but while developing you want to see the errors. (Also, don't print error.localizedDescription because it is less useful.)


Thank you @roosterboy! Didn't see the key mismatch, and also thanks for the helpful tip on using a do catch block instead of the if let since I was not getting any useful error before.


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