SwiftUI - Publish Background Thread Not Allowed - on code that does not update ui - swiftui

Question

New to swiftui and don't understand why the JSONDecoder() line in the first code throws
[SwiftUI] Publishing changes from background threads is not allowed; make sure to publish values from the main thread (via operators like receive(on:)) on model updates.
This to me is not updating ui so why is this showing?
do {
// pass the request type, bearer token, and email / password ( which are sent as POST body params )
let request = L.getRequest(requestType:"POST", token: token, email: self.username, password: self.psw)
L.fetchData(from: request) { result in
switch result {
case .success(let data):
// covert the binary data to a swift dictionary
do {
let response = try JSONDecoder().decode(WpJson.self, from: data)
for (key, title) in response.allowedReadings {
let vimeoId = Int( key )!
let vimeoUri = self.buildVimeoUri(vimeoId: key)
self.addReadingEntity(vimeoUri: vimeoUri, vimeoId: vimeoId, title: title)
}
self.writeToKeychain(jwt:response.jwt, displayName: response.displayName)
readings = self.fetchReadings()
}
catch {
self.error = error.localizedDescription
}
case .failure(let error):
self.error = error.localizedDescription
}
}
}
I tried wrapping a main queue around the do-catch in the L.fetchData(from: request) { result in but this did not help
DispatchQueue.main.async { [weak self] in
Here is the Login protocol, again without any ui work:
import Foundation
import SwiftUI
struct Login: Endpoint {
var url: URL?
init(url: URL?) {
self.url = url
}
}
protocol Endpoint {
var url: URL? { get set }
init(url: URL?)
}
extension Endpoint {
func getRequestUrl() -> URLRequest {
guard let requestUrl = url else { fatalError() }
// Prepare URL Request Object
return URLRequest(url: requestUrl)
}
func getRequest(requestType:String="POST", token:String, email:String="", password:String="") -> URLRequest {
var request = self.getRequestUrl()
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
if ( "" != email && "" != password && requestType == "POST") {
let parameters:[String:String?] = [
"email": email,
"password": password
]
// Run the request
do {
// pass dictionary to nsdata object and set it as request body
request.httpBody = try JSONSerialization.data(withJSONObject: parameters, options: .prettyPrinted)
} catch let error {
print(error.localizedDescription)
}
}
return request;
}
func fetchData(from request: URLRequest, completion: #escaping (Result<Data, NetworkError>) -> Void) {
URLSession.shared.dataTask(with: request) { data, response, error in
if let data = data {
completion(.success(data))
} else if error != nil {
// any sort of network failure
completion(.failure(.requestFailed))
} else {
// this ought not to be possible, yet here we are
completion(.failure(.unknown))
}
}.resume()
}
}
extension URLSession {
func dataTask(with request: URLRequest, completionHandler: #escaping (Result<(Data, HTTPURLResponse), Error>) -> Void) -> URLSessionDataTask {
return dataTask(with: request, completionHandler: { (data, urlResponse, error) in
if let error = error {
completionHandler(.failure(error))
} else if let data = data, let urlResponse = urlResponse as? HTTPURLResponse {
completionHandler(.success((data, urlResponse)))
}
})
}
}
Do you have any idea on how to fix this?

Answer 1

Wrap it right in place of assignment
catch {
DispatchQueue.main.async {
self.error = error.localizedDescription
}
}
case .failure(let error):
DispatchQueue.main.async {
self.error = error.localizedDescription
}
}