Swift Thread issues - ios

Question

I have a function where I download a picture from internet and I put it inside a UIImage, it also adds a website to the picture (UIButton). The Urls are stored in my DB and I store them in an Array. Then I generate a random number to get an index and use it to download the picture. I run the code in my viewDidLoad and it shows the picture and if I click it, it opens the webpage. I am also using a timer to repeat this function every 5 seconds so I was expecting it to display a different picture and website.
Unfortunately it keeps displaying the same picture (webpage is changed) and once in a while it changes the picture, but in console this message is displayed "This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread. This can lead to engine corruption and weird crashes."
What can I do to make this function work properly? I thank you all in advance. my code is the following
func descargaPicture(){
do {
let defaults = UserDefaults.standard
let miCIudad = defaults.object(forKey: "ciudad") as! String
let query = tblAd.filter(ciudad == miCIudad)
for infoAd in try conn.db!.prepare(query) {
//Guardar en arreglos
if(imagen.contains(infoAd[fotoAd]!)) {
print("ya existe")
} else {
imagen.append(infoAd[fotoAd]!)
}
if(web.contains(infoAd[webAd]!)){
} else {
web.append(infoAd[webAd]!)
}
} //Termina for
//-------------------------Descarga foto Internet-------------------------------
/*
Este proceso es similar a los anteriores, lo que hacemos es, después de obtener la imagen de nuestra BD, procedemos a hacer una petición para descargar la imagen del internet, así para poder después usarla como banner/Ad en determinadas Views, por lo que este bloque de código se encuentra presente en unas pocas clases de nuestro proyecto.
*/
let numero = imagen.count-1
if numero <= 0 {
print("El array esta vacio")
return
}
else {
var filtro = Int (arc4random_uniform(UInt32(numero)+1))
if imagen[filtro] != "" {
let picture = URL(string: self.imagen[filtro])!
let session = URLSession(configuration: .default)
let downloadPicTask = session.dataTask(with: picture) {(data, response, error) in
if let e = error {
print("Erro al descargar la imagen: \(e)")
}
else {
self.imagenAd.image = nil //-----------
if let res = response as? HTTPURLResponse {
print("Descargando foto, respuesta: \(res.statusCode)") //Da 200 como resp.
if let imageData = data {
let imagen = UIImage(data: imageData as Data)
self.imagenAd.image = imagen
self.webSite = self.web[filtro]
}
else {
print("No se puede obtener imagen")
}
}
else {
print("No se obtiene respuesta del servidor")
}
}
}
downloadPicTask.resume()
}
else {
print("Es NIL")
return
}
} //Cerramos el else definitivo
//--------------------/Descarga foto Internet ------------------------------
} //do
catch {
//Errores
}
}

Answer 1

The error says it all. You should do all UI related tasks on main thread.
Get hold of the main thread using
DispatchQueue.main.async {
//your UI Changes go here
}
And do all your UI Changes in this code block after getting the response.