API call function with completion handler crashes when accessed from different VC - ios

Question

Can someone fix my function code because I have created a API call function which will get the imageURL for the specific object in my class and display the results in the second view controller. I have created custom completion handler so that the code from second VC is only executed when dowloading of the imageURL is completed.
However, when I am testing this function in the second view controller to print me data that it has arrived I am getting a crash on the print statement line.
Here is the code for my API call function located in Model class file:
func parseImageData(finished: () -> Void) {
let urlPath = _exerciseURL
let url = URL(string: urlPath!)
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
if error != nil {
print("Error while parsing JSON")
}
else {
do {
if let data = data,
let fetchedImageData = try JSONSerialization.jsonObject(with: data, options: .mutableLeaves) as? [String:Any],
let images = fetchedImageData["results"] as? [[String: Any]] {
for eachImage in images {
let imageUrl = eachImage["image"] as! String
self._imageUrl = URL(string: imageUrl)
}
print(self._imageUrl)
}
}
catch {
print("Error while parsing data.")
}
}
}
task.resume()
finished()
}
And here in the second view controller I am just testing if I can access the code block:
override func viewDidLoad() {
super.viewDidLoad()
exercise.parseImageData() {
print("Arrived Here?") // I am getting crash on this line moving to debug navigator.
}
}

Answer 1

If the crash says something about force unwrapping nil then it's probably because let task = URLSession.shared.dataTask(with: url!) is unwrapping url which is a nil optional variable here.
But your completion handler is called in the wrong place anyway, try putting your finished() callback into the do statement instead. Because finished was executed the moment you called exercise.parseImageData()
if error != nil {
print("Error while parsing JSON")
}
else {
do {
if let data = data,
let fetchedImageData = try JSONSerialization.jsonObject(with: data, options: .mutableLeaves) as? [String:Any],
let images = fetchedImageData["results"] as? [[String: Any]] {
for eachImage in images {
let imageUrl = eachImage["image"] as! String
self._imageUrl = URL(string: imageUrl)
}
print(self._imageUrl)
finished()
}
}
catch {
print("Error while parsing data.")
}
}