How to return single.deferred in closure

Question

What am I doing wrong? How do I get the Single from the closure? How can I get value from Alamofire.request?

 func loadImageName(url: URL) -> Single<String> {
    let data = try? Data(contentsOf: url)
    guard let query = data else {
        return .error(Error.notFound)
    }

        ...

    return Single.deferred {
        Alamofire.request(request).responseJSON {
            if let error = $0.error {
                return Single<String>.error(error)
            }

            return Single<String>.just(result)
        }
    }
}

Answer 1

In this case you'll want Single.create.

This takes a block, which has a single argument. This argument is a function that you can call to pass a SingleEvent, i.e. either a .success(Element) (where Element is String in your case) or an .error.

The block must return a Disposable. You can construct a Disposable that will do additional work when it gets disposed. In the context of network requests, it makes sense to cancel the request.

func loadImageName(url: URL) -> Single<String> {
    let data = try? Data(contentsOf: url)
    guard let query = data else {
        return .error(Error.notFound)
    }

    // ...

    Single.create { single in
        let request = Alamofire.request(request).responseJSON {
            if let error = $0.error {
                return single(.error(error))
            }

            return single(.success(result))
        }

        return Disposables.create { request.cancel() }
    }
}