Repeat Network Request Multiple Times With Swift Combine - swift

Question

I'm trying to have a combine pipeline that fetches five random photo urls using the Unsplash API, then downloads a photo from each url. The issue I’m running into is that the images are mostly the same. Sometimes (and I don't know why) one of the images will be different than the other four.
Any help would be appreciated. I've included all the necessary code besides the UnSplash Api key.
static func fetchRandomPhotos() -> AnyPublisher<UIImage, Error>{
let string = createURL(path: "/photos/random")
return [1,2,3,4,5]
.publisher
.flatMap{ i -> AnyPublisher<UnsplashImageResults, Error> in
return self.downloadAndDecode(string, type: UnsplashImageResults.self)
}
.flatMap{ result -> AnyPublisher<UIImage, Error> in
print(result.urls.thumb)
let url = URL(string: result.urls.thumb)!
return URLSession.shared.dataTaskPublisher(for: url)
.map { UIImage(data: $0.data)! }
.mapError{_ in NetworkError.invalidURL}
.eraseToAnyPublisher()
}
.receive(on: RunLoop.main)
.eraseToAnyPublisher()
}
struct UnsplashURLs: Decodable{
let full: String
let regular: String
let small: String
let thumb: String
}
struct UnsplashImageResults: Decodable{
let urls: UnsplashURLs
}
enum NetworkError: LocalizedError{
case invalidURL
var errorDescription: String? {
switch self {
case .invalidURL:
return "The url is invalid"
}
}
}
static private func createURL(path: String)-> String{
var components = URLComponents()
components.scheme = "https"
components.host = "api.unsplash.com"
components.path = path
components.queryItems = [
URLQueryItem(name: "client_id", value: "YOUR API KEY HERE")
]
return components.string!
}
static private func downloadAndDecode<T:Decodable>(_ urlString: String, type: T.Type) -> AnyPublisher<T, Error>{
guard let url = URL(string: urlString) else{
return Fail(error: NetworkError.invalidURL).eraseToAnyPublisher()
}
return URLSession.shared.dataTaskPublisher(for: url)
.tryMap() { element -> Data in
guard let httpResponse = element.response as? HTTPURLResponse,
httpResponse.statusCode == 200 else {
throw URLError(.badServerResponse)
}
return element.data
}
.decode(type: T.self, decoder: JSONDecoder())
.receive(on: RunLoop.main)
.eraseToAnyPublisher()
}
class UnsplashImagesViewModel: ObservableObject{
var subscriptions = Set<AnyCancellable>()
#Published var images = [UIImage]()
init(){
UnsplashAPI.fetchRandomPhotos()
.sink { (_) in
} receiveValue: { image in
self.images.append(image)
}.store(in: &subscriptions)
}
}
struct UnsplashImagesGrid: View {
#StateObject private var model = UnsplashImagesViewModel()
var body: some View {
List(model.images, id: \.self){ image in
Image(uiImage: image)
}
}
}

Answer 1

Unsplash returns the same image, if you send multiple requests at the same time. You can test this behaviour by introducing a delay between your requests.
Anyway, you should be using the count param of Unsplash random API to request a particular number of images. I have made some changes to your code, to receive an array of UIImage. I hope this gives you an idea about, how it can improved further.
static func fetchRandomPhotos() -> AnyPublisher<[UIImage], Error>{
let string = createURL(path: "/photos/random")
return Just(())
.print()
.flatMap{ i -> AnyPublisher<[UnsplashImageResults], Error> in
return self.downloadAndDecode(string, type: UnsplashImageResults.self)
}
.flatMap{ results -> AnyPublisher<[UIImage], Error> in
let images = results.map { result -> AnyPublisher<UIImage, Error> in
let url = URL(string: result.urls.thumb)!
return URLSession.shared.dataTaskPublisher(for: url)
.map { UIImage(data: $0.data)! }
.mapError{_ in NetworkError.invalidURL}
.eraseToAnyPublisher()
}
return Publishers.MergeMany(images)
.collect()
.eraseToAnyPublisher()
}
.receive(on: RunLoop.main)
.eraseToAnyPublisher()
}
static private func createURL(path: String)-> String{
...
components.queryItems = [
URLQueryItem(name: "client_id", value: "ID"),
URLQueryItem(name: "count", value: "5")
]
...
}
static private func downloadAndDecode<T:Decodable>(_ urlString: String, type: T.Type) -> AnyPublisher<[T], Error>{
...
.decode(type: [T].self, decoder: JSONDecoder())
...
}