"Argument type string does not conform to expected type decoder" when trying to get JSON using codable protocol

Question

I'm trying to use Swift 4 Codable feature to get JSON but for some reason it creates an error that says:

Argument type string does not conform to expected type decoder

Here is my code:

Xcode Screenshot

import UIKit

struct aURL : Codable {
    let title: String
    let aurl: String
    //    let style: URLStyle
}

 class SectionTableViewController: UITableViewController {

 override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)

    do {
        let queue = DispatchQueue(label: "cool")
        queue.async {

            if let somedata = try? Data(contentsOf: URL(from: "http://json-schema.org/example/geo.json")!, options: []) {

                let json = try? JSONSerialization.jsonObject(with: somedata, options: [])
                print(json)

                DispatchQueue.main.async {

                }
            }

        }
    } catch let error as NSError {
        print("Error: \(error)")
    }

}

and if I try to fix it using Xcode suggested fix as shown in the image:

Xcode Screenshot

I get this error:

Xcode Screenshot

Could not cast value of type 'Swift.String' (0x1015acf68) to 'Swift.Decoder' (0x1015ec460).

vadian · Accepted Answer · 2018-01-19 14:46:21Z

3

There is a misunderstanding.

The URL API

init(from decoder: Decoder) throws

can only be used within the custom struct to create an URL from a given Decoder very similar to the init(coder API of the class related NSCoding protocol.

In the context to create an URL from a string you have to use URL(string

URL(string: "http://json-schema.org/example/geo.json")!

That's exactly what the error message says: I'm expecting a Decoder but I'm getting a String

Important note:

Never load data from a remote URL with the synchronous API Data(contentsOF: – not even in an asynchronous dispatch queue – and don't carelessly ignore errors with try?

edited Jan 19, 2018 at 14:46

answered Jan 19, 2018 at 14:39

vadian

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