Integrate Combine Into an App
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Next episode: 04. Use Publishers in the ViewModel
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Before we can use publishers in our view model, we have to define them first. We’ll need to use them in our production and test code, so some overarching protocols will work best here.
public protocol JokeServiceDataPublisher {
func publisher() -> AnyPublisher<Data, URLError>
}
public protocol TranslationServiceDataPublisher {
func publisher(for joke: Joke, to languageCode: String)
-> AnyPublisher<Data, URLError>
}
extension TranslationService: TranslationServiceDataPublisher {
public func publisher(for joke: Joke, to languageCode: String)
-> AnyPublisher<Data, URLError> {
URLSession.shared.dataTaskPublisher(
for: url(for: joke, languageCode: languageCode)
)
.map(\.data)
.eraseToAnyPublisher()
}
}
extension JokesService: JokeServiceDataPublisher {
public func publisher() -> AnyPublisher<Data, URLError> {
URLSession.shared
.dataTaskPublisher(for: url)
.map(\.data)
.eraseToAnyPublisher()
}
}
func publisher() -> AnyPublisher<Data, URLError> {
// 1
let publisher = CurrentValueSubject<Data, URLError>(data)
// 2
if let error = error {
publisher.send(completion: .failure(error))
}
// 3
return publisher.eraseToAnyPublisher()
}
func publisher(for joke: Joke, to languageCode: String) -> AnyPublisher<Data, URLError> {
// 1
let publisher = CurrentValueSubject<Data, URLError>(data)
// 2
if let error = error {
DispatchQueue.global().asyncAfter(deadline: .now() + 0.1) {
publisher.send(completion: .failure(error))
}
}
// 3
return publisher.eraseToAnyPublisher()
}