Call async func in another function and update UI - swiftui

Question

Here is my async function class:
class MoviesViewModel: ObservableObject {
#Published var topRated: [Movie] = []
#Published var popular: [Movie] = []
#Published var upcoming: [Movie] = []
func getUpcomingMovies() {
if let movies = getMovies(path: "upcoming") {
DispatchQueue.main.async {
self.upcoming = movies
}
}
}
func getPopularMovies() {
if let movies = getMovies(path: "popular") {
DispatchQueue.main.async {
self.popular = movies
}
}
}
func getTopRatedMovies() {
DispatchQueue.main.async {
if let movies = self.getMovies(path: "top_rated") {
self.topRated = movies
}
}
}
func getMovies(path: String) -> [Movie]? {
var movies: [Movie]?
let urlString = "https://api.themoviedb.org/3/movie/\(path)?api_key=\(apiKey)&language=en-US&page=1"
guard let url = URL(string: urlString) else { return [] }
let session = URLSession.shared
let dataTask = session.dataTask(with: url, completionHandler: { data, _, error in
if error != nil {
print(error)
}
do {
if let safeData = data {
let decodedData = try JSONDecoder().decode(NowPlaying.self, from: safeData)
DispatchQueue.main.async {
movies = decodedData.results
}
}
}
catch {
print(error)
}
})
dataTask.resume()
return movies
}
}
When I printed the movies in getMovies function, I can get movies from api without problem. However, UI does not update itself. I used DispatchQueue.main.async function but it did not solve my problem. What can I do in this situation?

Answer 1

dataTask works asynchronously. Your code returns nil even before the asynchronous task is going to start. You have to use a completion handler as described in Returning data from async call in Swift function.
I highly recommend to use async/await in this case. You get rid of a lot of boilerplate code and you don't need to care about dispatching threads.
#MainActor
class MoviesViewModel: ObservableObject {
#Published var topRated: [Movie] = []
#Published var popular: [Movie] = []
#Published var upcoming: [Movie] = []
func getUpcomingMovies() async throws {
self.upcoming = try await getMovies(path: "upcoming")
}
func getPopularMovies() async throws {
self.popular = try await getMovies(path: "popular")
}
func getTopRatedMovies() async throws {
self.topRated = try await getMovies(path: "top_rated")
}
func getMovies(path: String) async throws -> [Movie] {
let urlString = "https://api.themoviedb.org/3/movie/\(path)?api_key=\(apiKey)&language=en-US&page=1"
guard let url = URL(string: urlString) else { throw URLError(.badURL) }
let (data, _) = try await URLSession.shared.data(from: url)
return try JSONDecoder().decode(NowPlaying.self, from: data).results
}
}