Reactive Programming with Swift by Cecil Costa

Author:Cecil Costa [Costa, Cecil]
Language: eng
Format: azw3
Publisher: Packt Publishing
Published: 2016-04-28T04:00:00+00:00

Implementing the genre signal

Finally, we have to create the getGenreSignal function, which was used in the previous section. Here, as we know, this is a private function that returns a RACSignal and it will do a request to a specific URL; thus, we can start opening this function with the following code:

private func getGenreSignal() -> RACSignal { let url = NSURL(string: "https://api.themoviedb.org/3/genre/movie/list?api_key=\(self.apiKey)")!

Continue creating a signal, which is the one that will be returned, and using the NSURLSession for requesting the genre list with the following code:

return RACSignal.createSignal({ (subscriber: RACSubscriber!) -> RACDisposable! in let task = NSURLSession.sharedSession().dataTaskWithURL(url) { (data:NSData?, response: NSURLResponse?, error: NSError?) -> Void in

Once the request is done, we have to validate it. We can use the guard statement for controlling the input:

guard error == nil else { subscriber.sendError(error!) return } guard let data = data else { subscriber.sendError(NSError(domain: "app", code: 1, userInfo: nil)) return }

Finally, we can convert the received data into a Swift object (or objects); remember that this conversion can still fail, which will make us trap this error and send it as a signal error rather than propagating it as an exception:

do { let json = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions(rawValue: 0)) subscriber.sendNext(json) subscriber.sendCompleted() }catch let raisedError as NSError { subscriber.sendError(raisedError) } } // end dataTaskWithURL

As you know, a data task doesn't do anything without calling the resume method, and we all agree that it is a good time for doing this:

task.resume()

Finally, we can return the disposable that is required by the function definition. In this case, we have to cancel the request that is being done. After that, this function is done:

return RACDisposable(block: { () -> Void in task.cancel() }) }) } // end getGenreSignal } // end MovieDetailViewController

This View Controller is already done; however, as you can see, it requires some information that need to be sent from the first scene to the second one.

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