How to set an array's value from a JSON file? - ios

Question

I am building a SwiftUI app for iOS to help me and my classmates keep up with assignments.
The way I am syncing homework across devices is by pushing some JSON with the assignments into GitHub Pages and then the app parses the JSON code into a sleek and simple Section within a Form.
I would like to have the following JSON...
[
{
"subject": "Maths",
"content": "Page 142, exercises 4, 5, 6.",
"dueDate": "15/01/2022"
},
{
"subject": "English",
"content": "Write an essay about your favorite subject. 2 pages at least.",
"dueDate": "18/01/2022"
},
{
"subject": "Chemistry",
"content": "Learn every element from the Periodic Table.",
"dueDate": "16/01/2022"
}
]
... turn into something that looks like this:
The easiest way would be to create about 5 Sections and, if there aren't 5 assignments, leave them empty. This solution didn't work because not having 5 assignments in the JSON file means the function that handles the file would abort because JSONDecoder would return nil when unwrapping the 4th assignment.
I've been struggling for quite a while to find a solution. I tried this:
struct Assignments: Decodable {
let subject: [String]
let content: [String]
let dueDate: [String]
}
struct AssignmentView: View {
#State private var currentNumber = 0
#State private var numberOfAssignments = 0
#State private var subject = [""]
#State private var dueDate = [""]
#State private var content = [""]
func downloadAssignments() {
let assignemtURL = URL(string: "https://example.com/assignments.json")!
var assignmentRequest = URLRequest(url: assignmentURL)
assignmentRequest.httpMethod = "GET"
assignmentRequest.attribution = .developer
NSURLConnection.sendAsynchronousRequest(assignmentRequest, queue: OperationQueue.main) {(response, data, error) in
if error != nil {
print("Could not get assignments. :/")
} else {
guard let data = data else { return }
let assignmentJSON = "\(data)"
let jsonData = assignmentJSON.data(using: .utf8)!
let decodedAssignments: Assignments = try! JSONDecoder().decode(Assignments.self, from: jsonData)
let numberOfAssignments: Int = decodedAssignments.count
// Here comes the problem. How do I create an array / modify an existing array with each individual subject taken in order?
}
}
}
var body: some View {
let _ = downloadAssignments()
VStack {
Form {
Section {
ForEach(0..<numberOfAssignments) {
Text("\(subject[$0]) - Due \(dueDate[$0])")
.font(.system(size: 20, weight: .semibold))
Text("\(content[$0])")
}
}
}
}
}
}
}
How can I get the value of each variable from the JSON file and combine it into an array (example: var subjects = ["Maths", "English", "Chemistry"])?
I've been looking for an answer for weeks with no solution. Some help on this would be highly appreciated!

Answer 1

There are quite a few things to point out in your code. I'm afraid I can't present you a full solution, but these pointers might help you go into the right direction:
The structure of your Assignments model doesn't match the JSON (and is also not really easy to work with in the list). Instead of having a single model which has an array for each property, there should one model object per assignment
struct Assignment: Decodable {
let subject: String
let content: String
let dueDate: String
}
and then you can decode/store an array of those:
let decodedAssignments: [Assignment] = try! JSONDecoder().decode([Assignment].self, from: jsonData)
Triggering the download as a side-effect of the body being evaluated is not a good idea, because this does not happen only once. In fact, whenever you modify any state of the view it would re-trigger the download, basically leaving you in an infinite download-loop. Instead, a better place to start the download would be when the view appears:
var body: some View {
VStack {
// ...
}
.onAppear(perform: downloadAssignments)
}
NSURLConnection is an extreeeemly old API that you don't want to use nowadays (it has been officially deprecated for 6 years now!). Have a look at URLSession instead.