Problem converting JSON to Array with Swift

Question

I try to convert a JSON to an Array but I face some issue and do not know how to sort it out. I use Swift 5 and Xcode 12.2.

Here is the JSON from my PHP query:

 [ { Crewcode = AAA; Phone = 5553216789; Firstname = Philip; Lastname = MILLER; email = "[email protected]"; }, { Crewcode = BBB; Phone = 5557861243; Firstname = Andrew; Lastname = DEAN; email = "[email protected]"; } ]

And here is my Swift code :

 let url: URL = URL(string: "https://xxx.php")! let defaultSession = Foundation.URLSession(configuration: URLSessionConfiguration.default) let task = defaultSession.dataTask(with: url) { (data, response, error) in if error != nil { print("Failed to download data") } else { print("Data downloaded") do { if let jsondata = (try? JSONSerialization.jsonObject(with: data!, options: [])) { print(jsondata) struct Crew: Decodable { var Code: String var Phone: String var Firstname: String var Lastname: String var email: String } let decoder = JSONDecoder() do { let people = try decoder.decode([Crew].self, from: jsondata as! Data) print(people) } catch { print(error) } } } } } task.resume()

When I run my code I get the following error:

Could not cast value of type '__NSArrayI' (0x7fff86b930b0) to 'NSData' (0x7fff86b911e8). 2020-12-09 14:52:48.988468+0100 FTL[57659:3019805] Could not cast value of type '__NSArrayI' (0x7fff86b930b0) to 'NSData' (0x7fff86b911e8). Could not cast value of type '__NSArrayI' (0x7fff86b930b0) to 'NSData' (0x7fff86b911e8).

Should you have any idea to get it right, I thank you in advance for your assistance on this !

You're mixing JSONSerialization with JSONDecoder. These are not related (the former is a long-existing ObjC system; the latter is a newer Swift system). JSONDecoder expects you to pass the actual data to it. Remove the JSONSerialization code. But note that your struct requires that there be a Code parameter that your JSON doesn't include. If it's optional, then you need to make it optional (String?). — Rob Napier
– Rob Napier, Commented Dec 9, 2020 at 20:22

vadian · Accepted Answer · 2020-12-09 20:36:38Z

You are deserializing the JSON twice by mixing up JSONSerialization and JSONDecoder.

Delete the first one

~~if let jsondata = (try? JSONSerialization.jsonObject(with: data!, options: [])) {~~

– By the way the JSON in the question is neither fish nor fowl, neither JSON nor an NS.. collection type dump –

and replace

let people = try decoder.decode([Crew].self, from: jsondata as! Data)

with

let people = try decoder.decode([Crew].self, from: data!)

and the struct member names must match the keys otherwise you have to add CodingKeys

Thank you so much for your help! I tried and it works very well.

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