How to parse local JSON data in Swift? - json

Question

How to parse local JSON data where nested (optional) property is same as main.
Items data may be available or may not be available.
struct Category: Identifiable, Codable {
let id: Int
let name: String
let image: String
var items: [Category]?
}
I am using common Bundle extension to parse JSON data.
extension Bundle {
func decode<T: Codable>(_ file: String) -> T {
guard let url = self.url(forResource: file, withExtension: nil) else {
fatalError("Failed to locate \(file) in bundle.")
}
guard let data = try? Data(contentsOf: url) else {
fatalError("Failed to load \(file) from bundle.")
}
let decoder = JSONDecoder()
let formatter = DateFormatter()
formatter.dateFormat = "y-MM-dd"
decoder.dateDecodingStrategy = .formatted(formatter)
guard let loaded = try? decoder.decode(T.self, from: data) else {
fatalError("Failed to decode \(file) from bundle.")
}
return loaded
}
}
For eg data :
[
{
"id": 1,
"name": "Apple",
"image": "img_url",
"items" : [
{
"id": 1,
"name": "iPhone",
"image": "img_url",
"items" : [
{
"id": 1,
"name": "iPhone 11 Pro",
"image": "img_url"
},
{
"id": 2,
"name": "iPhone 11 Pro Max",
"image": "img_url"
}
]
},
{
"id": 2,
"name": "iPad",
"image": "img_url",
"items" : [
{
"id": 1,
"name": "iPad mini",
"image": "img_url"
},
{
"id": 2,
"name": "iPad Air",
"image": "img_url"
},
{
"id": 3,
"name": "iPad Pro",
"image": "img_url"
}
]
}
]
},
{
"id": 2,
"name": "Samsung",
"image": "img_url",
"items" : [
{
"id": 1,
"name": "Phone",
"image": "img_url"
},
{
"id": 2,
"name": "Tablet",
"image": "img_url"
}
]
}
]

Answer 1

Nesting is not the issue here, You are facing an Array of Contents. so you should pass [Content] to the decoder like:
let jsonDecoder = JSONDecoder()
try! jsonDecoder.decode([Category].self, from: json)
🎁 Property Wrapper
You can implement a simple property wrapper for loading and decoding all of your properties:
#propertyWrapper struct BundleFile<DataType: Decodable> {
let name: String
let type: String = "json"
let fileManager: FileManager = .default
let bundle: Bundle = .main
let decoder = JSONDecoder()
var wrappedValue: DataType {
guard let path = bundle.path(forResource: name, ofType: type) else { fatalError("Resource not found") }
guard let data = fileManager.contents(atPath: path) else { fatalError("File not loaded") }
return try! decoder.decode(DataType.self, from: data)
}
}
Now you can have any property that should be loaded from a file in a Bundle like:
#BundleFile(name: "MyFile")
var contents: [Content]
Note that since the property should be loaded from the bundle, I raised a FatalError. Because the only person should be responsible for these errors is the developer at the code time (not the run time).