Getting nil value when read JSON data in Swift - swift

Question

if let postString = NSString(data:data!, encoding: NSUTF8StringEncoding) as? String {
guard let jsonData = postString.dataUsingEncoding(NSASCIIStringEncoding) else {
fatalError()
}
guard let jsonObjects = try? NSJSONSerialization.JSONObjectWithData(jsonData,options: [])
,let JSONArray = jsonObjects as? [[String: AnyObject]]
else {
fatalError()
}
print(JSONArray)
}
In postString constant, I am getting "[{\"Name\":\"ABC\",\"Age\":35},{\"Name\":\"CDE\",\"Age\":36‌​}]"
and when I run this code then fatalError() code call.

Answer 1

A couple of other people have explained what you did wrong in this case (Tried to cast the output of deserialization to a dictionary when it actually contains an array.)
Stepping back from the details, when something fails, you need to break your code into smaller pieces and then trace through it to see what's failing.
The "as?" cast says "Try to cast this object to another type. Wrap the results in an Optional." If the cast fails, the result is nil. If it succeeds, the optional contains the new type.
If you rewrote your code as:
let jsonObject = try NSJSONSerialization.JSONObjectWithData(data!,
options: NSJSONReadingOptions.AllowFragments)
guard let jsonDict = jsonObject as [String: Any] else {
print("Cast failed")
return
}
Then the print statement would fire and you'd know that the cast was the problem.
EDIT:
I just noticed that your JSON data contains an array of dictionaries of type [String: Int]. In Swift Ints are not an Object type, so you need to cast your results to [[String:Any]], not [[String:AnyObject]]. I've fixed my code above.
I Wrote the following code in a playground and it works:
let jsonString = "[{\"Name\":\"ABC\",\"Age\":35},{\"surveyName\":\"CDE\",\"Age\":36}]"
guard let jsonData = jsonString.data(using: .ascii) else {
fatalError()
}
guard let jsonObjects = try? JSONSerialization.jsonObject(with: jsonData, options: []),
let JSONArray = jsonObjects as? [[String: Any]]
else {
fatalError()
}
print(String(describing: jsonObjects))
It gives the output:
(
{
Age = 35;
Name = ABC;
},
{
Age = 36;
surveyName = CDE;
}
)
Which is what I would expect.
EDIT #2:
Actually, on further investigation I'm stumped as to why your code isn't working. I just tested it, and the as [[String: AnyObject]] works. It turns out that in Swift 3 if you cast an Int to AnyObject and you've included Foundation (or UIKit) then it gets silently converted to an NSNumber, which IS an Object type.
You're going to need to show your actual JSON data and the code that converts it to an object if you need help debugging it.
EDIT #3:
Below is code I wrote and tested in Swift 2.3:
func parseJSONTest() {
let jsonString = "[{\"Name\":\"ABC\",\"Age\":35},{\"surveyName\":\"CDE\",\"Age\":36}]"
guard let jsonData = jsonString.dataUsingEncoding(NSASCIIStringEncoding) else {
fatalError()
}
//I'm not sure why you take JSON data, convert it to a string, and convert
//It back to NSData, but to prove a point, this is your code being fed
//well-formed JSON data in an NSData object:
if let postString = NSString(data:jsonData,
encoding: NSASCIIStringEncoding) as? String {
guard let jsonData = postString.dataUsingEncoding(NSASCIIStringEncoding) else {
fatalError()
}
guard let jsonObjects = try? NSJSONSerialization.JSONObjectWithData(jsonData,options: []),
let JSONArray = jsonObjects as? [[String: AnyObject]]
else {
fatalError()
}
print(JSONArray)
}
}
In order to provide a complete test I first take a string containing JSON data and convert it to NSData. I then convert that NSData back to JSON objects and cast them to the desired type, and it works. The code above displays:
[["Name": ABC, "Age": 35], ["surveyName": CDE, "Age": 36]]
Which matches the structure you have (an array of dictionaries).

Answer 2

The above is technically not an json object it is a json array.
Try casting as [AnyObject] instead of [String: AnyObject]
Then use the array to access the item you need. Then cast that to
[String:AnyObject]
because they are json objects within a json array