How to convert JSON array objects into list array

I have the following JSON array that is decoded from a URL, currently I am able to parse the array to access invisible object, but how can I recreate a list array of only trialid from the JSON. End result should look like: [27, 33]

The following is the structure of the JSON array:

[
  {
    "name": "mobile",
    "orderid": 1,
    "trialid": 27
  },
  {
    "name": "mobile",
    "orderid": 1,
    "trialid": 33
  }
]

The following is the what I am currently trying - how can foreach be performed here to loop through each object:

var structure = [testStructure]()

func fetch() {
        guard let url = URL(string: "test.com")
        else { return }
        
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.httpBody = "id=1".data(using: .utf8)
        URLSession.shared.dataTask(with: request) { data, _, error in
            guard let data = data else { return }
            
            do {
                let nav  = try JSONDecoder().decode(structure, from: data)
                
              
                    
                
            }
            catch {
                print(error)
            }
            
        }.resume()
        
    }


 struct testStructure: Decodable {
    let name: String?
    let orderid: Int?
    let trialid: Int?
}

UPDATE:

After converting into a list array, I am doing the following afterwards to initiate view controllers from Storyboards

   case .success( let data):
        do {
            let nav = try JSONDecoder().decode([TestStructure].self, from: data)
            self.viewControllers = (nav.map(\.trialid)) { "\($0)" }.map {
                
                let selected = UIImage(named: "Tab4_Large")!
                let normal = UIImage(named: "Tab4_Large")!
                let controller = storyboard!.instantiateViewController(withIdentifier: $0)
                controller.view.backgroundColor = UIColor.white
                controller.floatingTabItem = FloatingTabItem(selectedImage: selected, normalImage: normal)
                return controller
            }
            
        }
        
        catch {print(error)}

This is to overall build up a custom navigation bar

Issue 1:

Unable to infer complex closure return type; add explicit type to disambiguate

Issue 2:

Cannot call value of non-function type '[Int?]'

CodePudding user response：

First of all please name structs and classes always with starting uppercase letter and declare the struct members non-optional if the API sends consistent data

struct TestStructure: Decodable {
    let name: String
    let orderid: Int
    let trialid: Int
}

Second of all the decoding line doesn't compile, you have to write

let nav = try JSONDecoder().decode([TestStructure].self, from: data)

To get an array of all trialid values just map it

let allTrialids = nav.map(\.trialid)

Update: Take the compiler's advice and add explicit type to disambiguate

self.viewControllers = nav.map { test -> UIViewController in
    let selected = UIImage(named: "Tab4_Large")!
    let normal = UIImage(named: "Tab4_Large")!
    let controller = storyboard!.instantiateViewController(withIdentifier: String(test.trialid))
    controller.view.backgroundColor = UIColor.white
    controller.floatingTabItem = FloatingTabItem(selectedImage: selected, normalImage: normal)
    return controller
}

CodePudding user response：

Here is how I would make the Swift model representing your JSON object. I like to make my variables optional, so if they are not in the given JSON object array, it will not fail decoding. Depends if you have a consistent data source.

struct Element: Codable {
    var name: String?
    var orderid, trialid: Int?
}

To decode the above code use:

let elementList = try? JSONDecoder().decode([Element].self, from: data)

To be honest, I find it pretty tedious to create Swift models from JSON objects. I recommend you checkout QuickType. This online, free, tool will generate your Swift models from JSON objects. It works with other languages as well.

Edits: based on comments I removed TypeAlias for simplicity. I disagree that it is convoluted.