Fetch JSON Data not working

UI Frameworks SwiftUI
Jad-T OP
Created Dec ’20
Replies 11
Boosts 0
Views 2.4k
Participants 3
Hello
I don't get any error when I fetch data but when I run I don't see any data
Thank you 


Code Block 
import SwiftUI
import Combine
struct ContentView: View {
    @ObservedObject var networkController = NetworkController()
    @State var search: String = ""
    var body: some View {
        NavigationView{
            Form{
                Section(){
                    TextField("Search", text: $search)
                }
                Section(){
                    List(networkController.users.filter {
                            $0.state.contains(search) }
                         , id: \.state){ user in
                        Text(user.state)
                    }
                }
            }
            .navigationTitle("API")
        }
    }
}
class NetworkController: ObservableObject {
    private var can: AnyCancellable?
    
    let url = URL(string: "https://api.covidtracking.com/v1/states/current.json")!
    @Published var users = [User(state: "")]
    
    init() {
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            .replaceError(with: [])
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveValue: { users in
                self.users  = users
            })
    }
    
}
struct User: Decodable {
    var state: String
}


Answered by OOPer in 654511022
@Jad-T
Thanks for showing the result. The most important part is the value of completion at the bottom:
Code Block 
failure(Swift.DecodingError.valueNotFound(Swift.Int, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 3", intValue: 3), CodingKeys(stringValue: "deathConfirmed", intValue: nil)], debugDescription: "Expected Int value but found null instead.", underlyingError: nil)))

  • "Expected Int value but found null instead." means some value, which you expect as integer, was not an integer but null.

  • _JSONKey(stringValue: "Index 3", intValue: 3) represents that was in the fourth element of the JSON array.

  • CodingKeys(stringValue: "deathConfirmed", intValue: nil) states that the key was "deathConfirmed".

In fact, when I access the URL directory with browser, I get this:
Code Block 
[
  ...
  {
    "date": 20201227,
    "state": "AS",
    "positive": 0,
    "probableCases": null,
    "negative": 2140,
    "pending": null,
    "totalTestResultsSource": "totalTestsViral",
    "totalTestResults": 2140,
    "hospitalizedCurrently": null,
    "hospitalizedCumulative": null,
    "inIcuCurrently": null,
    "inIcuCumulative": null,
    "onVentilatorCurrently": null,
    "onVentilatorCumulative": null,
    "recovered": null,
    "dataQualityGrade": "D",
    "lastUpdateEt": "12/1/2020 00:00",
    "dateModified": "2020-12-01T00:00:00Z",
    "checkTimeEt": "11/30 19:00",
    "death": 0,
    "hospitalized": null,
    "dateChecked": "2020-12-01T00:00:00Z",
    "totalTestsViral": 2140,
    "positiveTestsViral": null,
    "negativeTestsViral": null,
    "positiveCasesViral": 0,
    "deathConfirmed": null,
    "deathProbable": null,
    "totalTestEncountersViral": null,
    "totalTestsPeopleViral": null,
    "totalTestsAntibody": null,
    "positiveTestsAntibody": null,
    "negativeTestsAntibody": null,
    "totalTestsPeopleAntibody": null,
    "positiveTestsPeopleAntibody": null,
    "negativeTestsPeopleAntibody": null,
    "totalTestsPeopleAntigen": null,
    "positiveTestsPeopleAntigen": null,
    "totalTestsAntigen": null,
    "positiveTestsAntigen": null,
    "fips": "60",
    "positiveIncrease": 0,
    "negativeIncrease": 0,
    "total": 2140,
    "totalTestResultsIncrease": 0,
    "posNeg": 2140,
    "deathIncrease": 0,
    "hospitalizedIncrease": 0,
    "hash": "2787ae39f1498a05878980d1f6195d5d78c19523",
    "commercialScore": 0,
    "negativeRegularScore": 0,
    "negativeScore": 0,
    "positiveScore": 0,
    "score": 0,
    "grade": ""
  },
  ...
]


Can you see "deathConfirmed": null,? The API may return null for "deathConfirmed".

Your model type needs to be ready for null:
Code Block 
struct User: Decodable, Hashable {
    var state: String
    var positive: Int
    var deathConfirmed: Int? //<-
}


Your DetailView needs to adapt to this change:
Code Block 
struct DetailView: View {
    
    var gridItemLayout = [GridItem(.flexible()), GridItem(.flexible())]
    
    var positive: Int
    var state: String
    var deathConfirmed: Int? //<-
    var body: some View {
        ...
                GroupBox{
                    VStack{
                        Text("State: ") //<-???
                        Divider()
                        Text(deathConfirmed.map{"\($0)"} ?? "?") //<-
                            .cornerRadius(16)
                    }
                }.padding()
            }
            .navigationBarTitle(state)
        }
    }
}



Replies  11
Boosts  0
Views  2.4k
Participants  3
Claude31 OP
Dec ’20
Have you checked the content you get at each step of:
Code Block 
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            .replaceError(with: [])
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveValue: { users in
                self.users  = users
            })


Who you paste code, please use Paste and Match Style, to avoid all the extra blank lines.

Code Block 
import SwiftUI
import Combine
struct ContentView: View {
    @ObservedObject var networkController = NetworkController()
    @State var search: String = ""
    var body: some View {
        NavigationView{
            Form{
                Section(){
                    TextField("Search", text: $search)
                }
                Section(){
                    List(networkController.users.filter {
                            $0.state.contains(search) }
                         , id: \.state){ user in
                        Text(user.state)
                    }
                }
            }
            .navigationTitle("API")
        }
    }
}
class NetworkController: ObservableObject {
    private var can: AnyCancellable?
    
    let url = URL(string: "https://api.covidtracking.com/v1/states/current.json")!
    @Published var users = [User(state: "")]
    
    init() {
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            .replaceError(with: [])
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveValue: { users in
                self.users  = users
            })
    }
    
}
struct User: Decodable {
    var state: String
}

0
Jad-T OP
Dec ’20
Still not working (I changed some code)
Code Block 
//
//  Charts
//
//  Created by Jad on 08/12/20.
//
import SwiftUI
import Combine
struct ContentView: View {
    @ObservedObject var networkController = NetworkController()
    @State var search: String = ""
    var body: some View {
        NavigationView{
            Form{
                Section(){
                    TextField("Search", text: $search)
                }
                Section(){
                    if search.isEmpty{
                        List(networkController.users, id: \.self){ user in
                            NavigationLink(destination: DetailView(positive: user.positive, deathConfirmed: user.deathConfirmed)){
                                    Text(user.state)
                            }
                        }
                    } else{
                        List(networkController.users.filter{$0.state.contains(search)}, id: \.self){ user in
                            NavigationLink(destination: DetailView(positive: user.positive, deathConfirmed: user.deathConfirmed)){
                                    Text(user.state)
                            }
                        }
                    }
                }
            }
            .navigationTitle("API")
        }
    }
}
class NetworkController: ObservableObject {
    private var can: AnyCancellable?
    
    let url = URL(string: "https://api.covidtracking.com/v1/states/current.json")!
    @Published var users = [User(state: "", positive: 0, deathConfirmed: 0)]
    
    init() {
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            .replaceError(with: [])
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveValue: { users in
                self.users  = users
            })
    }
    
}
struct User: Decodable, Hashable {
    var state: String
    var positive: Int
    var deathConfirmed: Int
}
//struct Records: Decodable, Hashable {
//    var countriesAndTerritories: String
//}


0
OOPer OP
Dec ’20

I don't get any error

You do not get any error because you are replacing error with empty result.
In the line marked as <- in your code:
Code Block 
   init() {
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            .replaceError(with: []) //<-
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveValue: { users in
                self.users  = users
            })
    }


Please try changing the lines above as follows and tell us what you see:
Code Block 
    init() {
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            //.replaceError(with: [])
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveCompletion: {completion in
                print(completion)
            }, receiveValue: { users in
                self.users  = users
            })
    }



0
Jad-T OP
Dec ’20
I still don't get an error but I can't see any data

Code:
Code Block 
//
//  Charts
//
//  Created by Jad on 08/12/20.
//
import SwiftUI
import Combine
struct ContentView: View {
    @ObservedObject var networkController = NetworkController()
    @State var search: String = ""
    var body: some View {
        NavigationView{
            Form{
                Section(){
                    TextField("Search", text: $search)
                }
                Section(){
                    if search.isEmpty{
                        List(networkController.users, id: \.self){ user in
                            NavigationLink(destination: DetailView(positive: user.positive, state: user.state, deathConfirmed: user.deathConfirmed)){
                                    Text(user.state)
                            }
                        }
                    } else{
                        List(networkController.users.filter{$0.state.contains(search)}, id: \.self){ user in
                            NavigationLink(destination: DetailView(positive: user.positive, state: user.state, deathConfirmed: user.deathConfirmed)){
                                    Text(user.state)
                            }
                        }
                    }
                }
            }
            .navigationTitle("API")
        }
    }
}
class NetworkController: ObservableObject {
    private var can: AnyCancellable?
    
    let url = URL(string: "https://api.covidtracking.com/v1/states/current.json")!
    @Published var users = [User(state: "", positive: 0, deathConfirmed: 0)]
    
    init() {
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            //.replaceError(with: [])
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveCompletion: {completion in
                print(completion)
            }, receiveValue: { users in
                self.users  = users
            })
    }
    
}
struct User: Decodable, Hashable {
    var state: String
    var positive: Int
    var deathConfirmed: Int
}
struct DetailView: View {
    
    var gridItemLayout = [GridItem(.flexible()), GridItem(.flexible())]
    
    var positive: Int
    var state: String
    var deathConfirmed: Int
    var body: some View {
        ScrollView{
            LazyVGrid(columns: gridItemLayout, spacing: 10){
                
                GroupBox{
                    VStack{
                        Text("State: ")
                        Divider()
                        Text(String(state))
                            .cornerRadius(16)
                    }
                }.padding()
                
                GroupBox{
                    VStack{
                        Text("Positive: ")
                        Divider()
                        Text(String(positive))
                            .cornerRadius(16)
                    }
                    
                }.padding()
                
                GroupBox{
                    VStack{
                        Text("State: ")
                        Divider()
                        Text(String(deathConfirmed))
                            .cornerRadius(16)
                    }
                }.padding()
            }
            .navigationBarTitle(state)
        }
    }
}


```
0
OOPer OP
Dec ’20

I still don't get an error but I can't see any data

Have you activated the Debug Console?
From the main menu of Xcode, View > Debug Area > Activate Console.

0
Jad-T OP
Dec ’20 
Code Block 
2020-12-28 14:36:28.125962+0100 Charts[47870:4787368] [] nw_protocol_get_quic_image_block_invoke dlopen libquic failed
2020-12-28 14:36:28.201001+0100 Charts[47870:4787265] [LayoutConstraints] Unable to simultaneously satisfy constraints.
	Probably at least one of the constraints in the following list is one you don't want. 
	Try this: 
		(1) look at each constraint and try to figure out which you don't expect; 
		(2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x600002f2fe30 'BIB_Trailing_CB_Leading' H:[_UIModernBarButton:0x7f86e8424430]-(6)-[_UIModernBarButton:0x7f86e8421fd0'API']   (active)>",
    "<NSLayoutConstraint:0x600002f2fe80 'CB_Trailing_Trailing' _UIModernBarButton:0x7f86e8421fd0'API'.trailing <= _UIButtonBarButton:0x7f86e8411020.trailing   (active)>",
    "<NSLayoutConstraint:0x600002f0cc80 'UINav_static_button_horiz_position' _UIModernBarButton:0x7f86e8424430.leading == UILayoutGuide:0x60000351f1e0'UIViewLayoutMarginsGuide'.leading   (active)>",
    "<NSLayoutConstraint:0x600002f0ccd0 'UINavItemContentGuide-leading' H:[_UIButtonBarButton:0x7f86e8411020]-(0)-[UILayoutGuide:0x60000351f100'UINavigationBarItemContentLayoutGuide']   (active)>",
    "<NSLayoutConstraint:0x600002f3d950 'UINavItemContentGuide-trailing' UILayoutGuide:0x60000351f100'UINavigationBarItemContentLayoutGuide'.trailing == _UINavigationBarContentView:0x7f86e8610bf0.trailing   (active)>",
    "<NSLayoutConstraint:0x600002f0d450 'UIView-Encapsulated-Layout-Width' _UINavigationBarContentView:0x7f86e8610bf0.width == 0   (active)>",
    "<NSLayoutConstraint:0x600002f3dd10 'UIView-leftMargin-guide-constraint' H:|-(0)-[UILayoutGuide:0x60000351f1e0'UIViewLayoutMarginsGuide'](LTR)   (active, names: '|':_UINavigationBarContentView:0x7f86e8610bf0 )>"
)
Will attempt to recover by breaking constraint 
Error:
<NSLayoutConstraint:0x600002f2fe30 'BIB_Trailing_CB_Leading' H:[_UIModernBarButton:0x7f86e8424430]-(6)-[_UIModernBarButton:0x7f86e8421fd0'API']   (active)>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.
failure(Swift.DecodingError.valueNotFound(Swift.Int, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 3", intValue: 3), CodingKeys(stringValue: "deathConfirmed", intValue: nil)], debugDescription: "Expected Int value but found null instead.", underlyingError: nil)))

0
Claude31 OP
Dec ’20
I tested in playground and got nothing.
Problem is probably your line 41.

I modified like this and seemed to work much better when appending after completion:

Code Block 
var users : [User] = []
let can = URLSession.shared.dataTaskPublisher(for: uUrl)
    .map { $0.data }
    .decode(type: [User].self, decoder: JSONDecoder())
    .replaceError(with: [])
    .eraseToAnyPublisher()
    .receive(on: DispatchQueue.main)
    .sink(receiveCompletion: { print ("Received completion: \($0)."); print(users.count, users[1]) },
          receiveValue: { user in print ("Received user: \(user).") ; users.append(contentsOf: user)
          })

print gives:
56 User(state: "AL")

Note: see this https://developer.apple.com/documentation/foundation/urlsession/processing_url_session_data_task_results_with_combine
0
Jad-T OP
Dec ’20
Still not working

Code Block 
struct User: Decodable, Hashable {
    var state: String
    var positive: Int
    var deathConfirmed: Int
}

I don't know why but when I delete deathConfirmed it works

0
OOPer OP
Dec ’20
Accepted Answer
@Jad-T
Thanks for showing the result. The most important part is the value of completion at the bottom:
Code Block 
failure(Swift.DecodingError.valueNotFound(Swift.Int, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 3", intValue: 3), CodingKeys(stringValue: "deathConfirmed", intValue: nil)], debugDescription: "Expected Int value but found null instead.", underlyingError: nil)))

  • "Expected Int value but found null instead." means some value, which you expect as integer, was not an integer but null.

  • _JSONKey(stringValue: "Index 3", intValue: 3) represents that was in the fourth element of the JSON array.

  • CodingKeys(stringValue: "deathConfirmed", intValue: nil) states that the key was "deathConfirmed".

In fact, when I access the URL directory with browser, I get this:
Code Block 
[
  ...
  {
    "date": 20201227,
    "state": "AS",
    "positive": 0,
    "probableCases": null,
    "negative": 2140,
    "pending": null,
    "totalTestResultsSource": "totalTestsViral",
    "totalTestResults": 2140,
    "hospitalizedCurrently": null,
    "hospitalizedCumulative": null,
    "inIcuCurrently": null,
    "inIcuCumulative": null,
    "onVentilatorCurrently": null,
    "onVentilatorCumulative": null,
    "recovered": null,
    "dataQualityGrade": "D",
    "lastUpdateEt": "12/1/2020 00:00",
    "dateModified": "2020-12-01T00:00:00Z",
    "checkTimeEt": "11/30 19:00",
    "death": 0,
    "hospitalized": null,
    "dateChecked": "2020-12-01T00:00:00Z",
    "totalTestsViral": 2140,
    "positiveTestsViral": null,
    "negativeTestsViral": null,
    "positiveCasesViral": 0,
    "deathConfirmed": null,
    "deathProbable": null,
    "totalTestEncountersViral": null,
    "totalTestsPeopleViral": null,
    "totalTestsAntibody": null,
    "positiveTestsAntibody": null,
    "negativeTestsAntibody": null,
    "totalTestsPeopleAntibody": null,
    "positiveTestsPeopleAntibody": null,
    "negativeTestsPeopleAntibody": null,
    "totalTestsPeopleAntigen": null,
    "positiveTestsPeopleAntigen": null,
    "totalTestsAntigen": null,
    "positiveTestsAntigen": null,
    "fips": "60",
    "positiveIncrease": 0,
    "negativeIncrease": 0,
    "total": 2140,
    "totalTestResultsIncrease": 0,
    "posNeg": 2140,
    "deathIncrease": 0,
    "hospitalizedIncrease": 0,
    "hash": "2787ae39f1498a05878980d1f6195d5d78c19523",
    "commercialScore": 0,
    "negativeRegularScore": 0,
    "negativeScore": 0,
    "positiveScore": 0,
    "score": 0,
    "grade": ""
  },
  ...
]


Can you see "deathConfirmed": null,? The API may return null for "deathConfirmed".

Your model type needs to be ready for null:
Code Block 
struct User: Decodable, Hashable {
    var state: String
    var positive: Int
    var deathConfirmed: Int? //<-
}


Your DetailView needs to adapt to this change:
Code Block 
struct DetailView: View {
    
    var gridItemLayout = [GridItem(.flexible()), GridItem(.flexible())]
    
    var positive: Int
    var state: String
    var deathConfirmed: Int? //<-
    var body: some View {
        ...
                GroupBox{
                    VStack{
                        Text("State: ") //<-???
                        Divider()
                        Text(deathConfirmed.map{"\($0)"} ?? "?") //<-
                            .cornerRadius(16)
                    }
                }.padding()
            }
            .navigationBarTitle(state)
        }
    }
}



1
Claude31 OP
Dec ’20
So, your init would be

Code Block 
    init() {
        var receivedUsers : [User] = []
        self.can = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: [User].self, decoder: JSONDecoder())
            .replaceError(with: [])
            .eraseToAnyPublisher()
            .receive(on: DispatchQueue.main)
            .sink(receiveCompletion: { _ in users = receivedUsers },
                    receiveValue: { user in receivedUsers.append(contentsOf: user)
          })
    }


On your posts:

  • when you reply, please tell which proposal you replied to

  • don't just say "it doesn't work". Take time, as those who answer to help you, to explain what you exactly tried, what you get,

0
Jad-T OP
Dec ’20
Thank you very much
It worked
0
Fetch JSON Data not working
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