How Do I Return This JSON Output Out of The "Do" Call In Swift?

Question

I've spent the last few hours working on retrieving the contents of a JSON and puts it into an array. Now that I've finally got it, I have no idea how to get the variable "students" that contains the array. I want to be able to return this variable back to the viewDidLoad function. Can you please help?

class ViewController: UIViewController {


struct Student: Decodable {
    let Name: String?
    let Gender: String
    let SRT, RST, Accuracy: Double
    let AttentionLevel: Int
    let FavoriteSubject, LeastFavoriteSubject: String

}


struct Student: Decodable {
    let Name: String
    let Score: Int
}
override func viewDidLoad() {
    super.viewDidLoad()

    getJSONFromOnline()

    
}

func getJSONFromOnline(){
    let jsonURLString = "insert example URL String here" //(I'm using a GitHub Pages site to host the students' data)
    
    let url = URL(string: jsonURLString)
    
    URLSession.shared.dataTask(with: url!){
        (data, response, err) in
        
        guard let data = data else {return}
        
        do {
            let students = try JSONDecoder().decode([Student].self, from: data)
            //How do I get this ^^^ variable back to the viewDidLoad function?
        }
        
        catch let jsonErr{
            print("error serializing", jsonErr)
        }
    }.resume()

}

}

Frankenstein Frankenstein · Accepted Answer · 2020-07-22T21:36:39

Add an @escaping completion block to the getJSONFromOnline method and use the closure block the get the students in viewDidLoad.

class ViewController: UIViewController {
    //...
    override func viewDidLoad() {
        super.viewDidLoad()

        getJSONFromOnline { students in
            print("got students", students)
        }
    }

    func getJSONFromOnline(completion: @escaping ([Student]) -> Void) {
        //...
        let students = try JSONDecoder().decode([Student].self, from: data)
        completion(students)
        //...
    }
}

Add-on: It would be better to name the method some a bit more specific, like getStudents or fetchStudents. Also, move the struct Student declaration outside of the ViewCotroller.

How Do I Return This JSON Output Out of The "Do" Call In Swift?

1 Answers