无法快速从 JSON 中正确提取数据

Question

I have a this kind of json object in my response after parsing json string to object

[
    "requestId": 1, 
    "response": {
        code = SUCCESS;
    }, 
    "messageId": ACTION_COMPLETE
]

I am trying to extract requestId using

responseMsg["requestId"] as! Int

I am getting this error

Could not cast value of type 'NSTaggedPointerString' (0x21877a910) to 'NSNumber' (0x218788588).

I tried it changing to Int(responseMsg["requestId"] as! String)! This thing is working for positive numbers but not for negative numbers probably bcz when requestId = -2 it throws me an error

Could not cast value of type '__NSCFNumber' (0x21877a000) to 'NSString' (0x218788290).

I tried with different other solution too but did not work.

Answer 1

For parsing the JSON data , its better use Codable instead of manually parsing everything.

For JSON format ,

{
    "requestId": 1,
    "response": {
        "code":"SUCCESS"
    },
    "messageId": "ACTION_COMPLETE"
}

Create Models like,

struct Root: Decodable {
    let requestId: String?
    let messageId: String
    let response: Response

    enum CodingKeys: String, CodingKey {
        case requestId, messageId, response
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        if let id = try? values.decode(Int.self, forKey: .requestId) {
            requestId = String(id)
        } else if let id = try? values.decode(String.self, forKey: .requestId) {
            requestId = id
        } else {
            requestId = nil
        }
        messageId = try values.decode(String.self, forKey: .messageId)
        response = try values.decode(Response.self, forKey: .response)
    }
}

Now, parse the JSON data using,

do {
    let root = try JSONDecoder().decode(Root.self, from: data)
    print(root.requestId) //access requestId like this....
} catch {
    print(error)
}

Answer 2

Try

Int(String(describing: responseMsg["requestId"]))!

This ensures any data is converted to string first and then to int

Answer 3

This error message

Could not cast value of type 'NSTaggedPointerString' (0x21877a910) to 'NSNumber' (0x218788588).

tells us that the JSON request id is being parsed as a string. NSTaggedPointerString is a special internal type used by the ObjC runtime to represent strings.

Try this:

let requestId = responseMsg["requestId"] as! String
print("request id: \(requestId)") // Prints a string

Note, it may print something that looks like a number, but it isn't one.

The JSON you are parsing probably looks like

{
    "requestId": "1", 
    "response": {
        "code" = "SUCCESS"
    }, 
    "messageId": "ACTION_COMPLETE"
}

Note the 1 in quotes.

Answer 4

Swift 5

String interpolation is what worked for me! (casting it first to String didn't work as I had other values for which the json decoder actually did its job and cast them directly to a number)

if let responseMsg_any = responseMsg["requestId"], 
   let responseMsg_int = Int("\(responseMsg_any)") {
   //..
}

Warning:

This solution allows any Type to become a String and be checked for a Int value. Only use this if you're not concerned about the value's Type prior to interpolation.