'NSInvalidArgumentException', reason: 'Invalid type in JSON write (__SwiftValue)'

Question

I am getting the following error when I try to encode an object.

'NSInvalidArgumentException', reason: 'Invalid type in JSON write (__SwiftValue)'

The definition of this object is as under:-

public struct Item: Codable {
    public var _id: Int
    public var name: String
    public var price: Float

    public init(_id: Int, name: String, price: Float) {
        self._id = _id
        self.name = name
        self.price = price
    }    

    public enum CodingKeys: String, CodingKey {
        case _id = "id"
        case name
        case price
    }
}

And I am trying to encode it by:

public func createDictionaryRequestForAddingItems(item : Item)->Data{
    let dictRequest = ["item":item];
    let dataRequest = try! JSONSerialization.data(withJSONObject: dictRequest, options: []);
    return dataRequest;
}

If instead of an item object I use a simple object like a String or an Int directly, then it all works, but when the request needs an Item object (which IS-A Codable instance) then it gives the above error.

JSONSerialization.isValidJSONObject(item) always gives false, even for the requests that getting properly getting encoded.

Answer 1

The problem is that you are trying to combine two types of JSON encoding. JSONSerialization and Codable. JSONSerialization has nothing to do with Codable.

Actually, you want something like this:

public func createDictionaryRequestForAddingItems(item: Item) -> Data {
   let dictRequest = ["item": item]
   let dataRequest = try! JSONEncoder().encode(dictRequest)
   return dataRequest
}

JSONSerialization can encode only the following types: Array, Dictionary, String, Bool and numeric types (e.g. Double, Int).