How can I access values within Optional NSSingleObjectArrayI? - ios

Question

I do not know how to access the 'duration' value within my nested Optional NSSingleObjectArrayI that is constructed from a JSON response. How do I access the nested values within this data structure?
When I call print(firstRow["elements"]), I get the following output:
Optional(<__NSSingleObjectArrayI 0x60000120f920>(
{
distance = {
text = "1.8 km";
value = 1754;
};
duration = {
text = "5 mins";
value = 271;
};
"duration_in_traffic" = {
text = "4 mins";
value = 254;
};
status = OK;
}
))
I have tried string indexing (firstRow['elements']['duration']) but am getting errors.
fetchData { (dict, error) in
if let rows = dict?["rows"] as? [[String:Any]]{
if let firstRow = rows[0] as? [String:Any]{
print("firstRow is")
print(firstRow["elements"])
// Trying to access duration within firstRow['elements'] here
}
}
}
For reference, this is the fetchData function:
func fetchData(completion: #escaping ([String:Any]?, Error?) -> Void) {
let url = getRequestURL(origin: "test", destination: "test")!;
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do {
if let array = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String:Any]{
completion(array, nil)
}
} catch {
print(error)
completion(nil, error)
}
}
task.resume()
}
A sample HTTP JSON request is here:
https://maps.googleapis.com/maps/api/distancematrix/json?destinations=77%20Massachusetts%20Ave,%20Cambridge,%20MA&departure_time=now&key=AIzaSyB65D4XHv6PkqvWJ7C-cFvT1QHi9OkqGCE&origins=428%20Memorial%20Dr,%20Cambridge,%20MA

Answer 1

Seeing your output, your firstRow["elements"] is Optional, so you need to unwrap it. And it actually is an NSArray with a single element, where the only element is a Dictionary, with 4 entries -- "distance", "duration", "duration_in_traffic" and "status". You may need to cast the element to a Dictionary to access each entry.
You may use Optional binding with as?-casting for this purpose:
fetchData { (dict, error) in
if let rows = dict?["rows"] as? [[String: Any]] {
if let firstRow = rows.first {
print("firstRow is")
print(firstRow["elements"])
//Unwrap and cast `firstRow["elements"]`.
if let elements = firstRow["elements"] as? [[String: Any]] {
//The value for "duration" is a Dictionary, you need to cast it again.
if let duration = elements.first?["duration"] as? [String: Any] {
print(duration["text"] as? String)
print(duration["value"] as? Int)
}
}
}
}
}
Or too deeply nested ifs are hard to read, so someone would like it as:
fetchData { (dict, error) in
if
let rows = dict?["rows"] as? [[String: Any]],
let firstRow = rows.first,
let elements = firstRow["elements"] as? [[String: Any]],
let duration = elements.first?["duration"] as? [String: Any]
{
print(duration["text"] as? String)
print(duration["value"] as? Int)
}
}
Or using guard may be a better solution.
Or else, if you can show us the whole JSON text in a readable format, someone would show you how to use Codable, which is a modern way to work with JSON in Swift.