Empty List from JSON in SwiftUI

Question

I'm having some trouble fetching data from the PiHole API;

This is the JSON format (from the url http://pi.hole/admin/api.php?summary ):

{
  "domains_being_blocked": "1,089,374",
  "dns_queries_today": "34,769",
  "ads_blocked_today": "11,258",
  "ads_percentage_today": "32.4",
  "unique_domains": "9,407",
  "queries_forwarded": "17,972",
  "queries_cached": "5,539",
  "clients_ever_seen": "35",
  "unique_clients": "23",
  "dns_queries_all_types": "34,769",
  "reply_NODATA": "1,252",
  "reply_NXDOMAIN": "625",
  "reply_CNAME": "10,907",
  "reply_IP": "21,004",
  "privacy_level": "0",
  "status": "enabled",
  "gravity_last_updated": {
    "file_exists": true,
    "absolute": 1588474361,
    "relative": {
      "days": "0",
      "hours": "14",
      "minutes": "18"
    }
  }
}

This is my code:

ContentView.swift

import SwiftUI

struct NetworkController {
    static func fetchData(completion: @escaping (([PiHole.Stat]) -> Void)) {
       if let url = URL(string: "http://pi.hole/admin/api.php?summary") {
          URLSession.shared.dataTask(with: url) { (data, response, error) in

            if let data = data {
                let stat = try? JSONDecoder().decode(PiHole.self, from: data)
                completion(stat?.stats ?? [])
            }
          }.resume()
       }
    }
}

class ContentViewModel: ObservableObject {
    @Published var messages: [PiHole.Stat] = []

    func fetchData() {
        NetworkController.fetchData { messages in
            DispatchQueue.main.async {
                self.messages = messages
            }
        }
    }
}

struct ContentView: View {

    @ObservedObject var viewModel = ContentViewModel()

    var body: some View {
        List {
            ForEach(viewModel.messages, id: \.self) { stat in
                Text(stat.domains_being_blocked)
            }
        }.onAppear{
            self.viewModel.fetchData()
        }
    }
}

Data.swift

struct PiHole: Decodable {
    var stats: [Stat]

    struct Stat: Decodable, Hashable {
        var domains_being_blocked: String
        var ads_percentage_today: String
        var ads_blocked_today: String
        var dns_queries_today: String
    }
}

Everything seems okay, no errors, yet when I run it, the simulator only shows an empty list

In Playground I can retrieve those data just fine:

import SwiftUI

struct PiHoleTest: Codable {
    let domains_being_blocked: String
    let ads_blocked_today: String
}

let data = try! Data.init(contentsOf: URL.init(string: "http://pi.hole/admin/api.php?summary")!)

do {
    let decoder: JSONDecoder = JSONDecoder.init()
    let user: PiHoleTest = try decoder.decode(PiHoleTest.self, from: data)

    print("In Blocklist \(user.domains_being_blocked)")
    print("Blocked Today: \(user.ads_blocked_today) ")


} catch let e {
    print(e)
}

The Output:

In Blocklist 1,089,374
Blocked Today: 11,258

What am I doing wrong? Or better, is there another way to fetch these stats?

Thanks in Advance!

Answer 1

The issue was related to the structure. Your JSON decoded were not an array. So PiHole struct was unnecessary. I can tested and this code is working now.

import SwiftUI

struct NetworkController {
    static func fetchData(completion: @escaping ((Stat) -> Void)) {
        if let url = URL(string: "http://pi.hole/admin/api.php?summary") {
            let request = URLRequest(url: url)
            URLSession.shared.dataTask(with: request) { (data, response, error) in
                do {
                    if let data = data {
                        let stat = try JSONDecoder().decode(Stat.self, from: data)
                        DispatchQueue.main.async() {
                            completion(stat)
                        }
                        return
                    } else {
                        print("Error Found")
                    }
                } catch let error as NSError {
                    print(error.localizedDescription)
                }
            }.resume()
        }
    }
}

class ContentViewModel: ObservableObject {
    @Published var stat: Stat? = nil
    func fetchData() {
        NetworkController.fetchData { stat in
            self.stat = stat
        }
    }
}

struct TestView: View {
    @ObservedObject var viewModel = ContentViewModel()
    var body: some View {
        List {
            Text(viewModel.stat?.domains_being_blocked ?? "No Data")
            Text(viewModel.stat?.ads_blocked_today ?? "No Data")
            Text(viewModel.stat?.ads_percentage_today ?? "No Data")
            Text(viewModel.stat?.dns_queries_today ?? "No Data")
        }.onAppear{
            self.viewModel.fetchData()
        }
    }
}

struct Stat: Decodable, Hashable {
    var domains_being_blocked: String
    var ads_percentage_today: String
    var ads_blocked_today: String
    var dns_queries_today: String
}