How to parse JSON using init() - ios

Question

I can't display the json Array by using its object
showing this error :
"Thread 1: Fatal error: Unexpectedly found nil while unwrapping an
Optional value"
class sample{
var jarray:[[String:Any]]!
init(url: String) {
let urll = URL(string: url)
var request = URLRequest(url: urll!)
request.httpMethod = "GET"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
let task = URLSession.shared.dataTask(with: request, completionHandler: {(Data,response,Error) in
do
{
let jsonresponse = try JSONSerialization.jsonObject(with: Data!, options: [])
let jsonarray = jsonresponse as? [[String:Any]]
self.jarray = jsonarray!
print(self.jarray)
DispatchQueue.main.async {
}
}
catch let parsingerror
{
print("error",parsingerror)
}
})
task.resume()
}
}

Answer 1

First of all: Handle always errors and unwrap optionals safely.
Second of all Data and Error (capitalized) are reserved words, use always lowercased parameter labels in closures (and uppercased class names).
Many lines in your code are redundant.
class Sample {
var jarray = [[String:Any]]()
init(url: String) {
guard let urll = URL(string: url) else { return }
let task = URLSession.shared.dataTask(with: urll) { data, _ , error in
if let error = error { print(error); return }
do
{
// if error is nil then data is guaranteed to be non-nil
if let jsonarray = try JSONSerialization.jsonObject(with: data!) as? [[String:Any]] {
self.jarray = jsonarray
print(self.jarray)
DispatchQueue.main.async {
}
}
}
catch {
print("error", error)
}
}
task.resume()
}
}
Note: It's bad practice to run asynchronous tasks in init methods

Answer 2

Avoid using force unwrapping unnecessarily. I might result in unwanted crashes in your app. In your code,
Check if Data is nil. If it is, the below line will result in runtime exception.
let jsonresponse = try JSONSerialization.jsonObject(with: Data!, options: [])
In the below line of code, check whether jsonarray is nil.
self.jarray = jsonarray!
If not, then add the line where your app is crashing.
Try replacing your code with:
class sample {
var jarray: [[String:Any]]?
init(url: String) {
if let urll = URL(string: url) {
URLSession.shared.dataTask(with: urll) { (data, response, error) in
do {
if let data = data {
let jsonresponse = try JSONSerialization.jsonObject(with: data, options: [])
self.jarray = jsonresponse as? [[String:Any]]
print(self.jarray)
DispatchQueue.main.async {
}
}
} catch {
print("error",error)
}
}.resume()
}
}
}
Also, don't use reserved words as variable names like you did for Data and Error.
Most importantly - Never use forced unwrapping (!) with server response. API response might not be as expected always. Try handling that.

Answer 3

JSONSerialization is now old-fashioned way. Apple introduced Codable protocol that handles for you serialisation and deserialisation of objects.
Example:
struct Photo: Codable
{
//String, URL, Bool and Date conform to Codable.
var title: String
var url: URL
var isSample: Bool
//The Dictionary is of type [String:String] and String already conforms to Codable.
var metaData: [String:String]
//PhotoType and Size are also Codable types
var type: PhotoType
var size: Size
}
And in the response from the server:
if let jsonData = jsonString.data(using: .utf8)
{
let photoObject = try? JSONDecoder().decode(Photo.self, from: jsonData)
}