Tagged with combine, rxswift, swift, ios. Let’s setup an example below on how to test out these cache headers: ... Those of you who have already been using RxSwift … At this point, the network request hasn’t been executed yet! Each of these parameters has a distinct purpose: The nature of HTTP requests is flaky, to say the least. This is some data, typically text, that’s sent as part of the request message. And if you want to inspect or mock requests and webservice APIs, check out the excellent Paw app. Just for fun, let’s check out what we’re actually getting back in the completion handler. You’ll see how we deal with this, later on. You see that there’s a great number of errors that can occur, and you’ll need to validate most if not all of them. In the above code we’re creating an upload task with session.uploadTask(..., and provide request and jsonData as parameters. Take a look, Android Image Color Change With ColorMatrix, AoGProTips: Synchronize animations with the Text-To-Speech. This is an object which provides all of the configuration for the URLSession. Now you are probably asking yourself what this has to do with offline caching? In our case, it’ll be a JSON object that’s sent as a Data object. In WWDC 2019 Apple introduced their very own FRP framework, making it possible to utilize the paradigm natively with declarative Swift API. RxSwift-to-SwiftUI MVP Demo App. The AnyPublisher requires us to specify the Failure error type while the Observable only takes the generic Elementtype. The fact the date headers are the same shows that the second request response is in fact the same response as the first request, it has just been fetched from the cache. to disable error handling, but keep in mind that in a production app you’ll need to handle errors appropriately. If we take another look at our example with the additional 2 snippets above we should have something like below: Now if we follow the same test as before: What we should see in the console is this: Now that we have shown how to grab cached requests from the cache, let’s wrap this up in a nice way so we can reuse it if we wish. When he’s not coding, he enjoys strong espresso and traveling. When the above code is executed, this is printed out: OK, let’s do some validation in the completion handler. In this tutorial, to use URLSession the Rx way, you will simply use a solution boxed with RxCocoa — RxSwift’s companion library. So how can we get around this? However this time, as the request has failed we are fetching the previously made request response from the cache and outputting the header from that. When a function’s last parameter accepts a closure, you can write that closure outside the functions parentheses (). Sign up for my iOS development course, and learn how to build great iOS 14 apps with Swift 5 and Xcode 12. Learn more ». We can use this to prove how the caching works in URLSession. Reinder de Vries is a professional iOS developer. If you peek into GitFeed ’s Podfile, you will notice that you import two different CocoaPods: RxSwift and RxCocoa . Now you could build some custom caching layer that writes things to disk or a library such as PINCache. If you peek into GitFeed ’s Podfile, you will notice that you import two different CocoaPods: RxSwift and RxCocoa . First, note that we’re assigning the return value of dataTask(with:completionHandler:) to the task constant. Instead we are receiving an error. It is an in-memory and on-disk cache of the responses from URLRequests. RxSwift Abstractions . In this post we are going to extend that simple networking example to include some offline caching so that if our network requests fail we can still provide content. This is because we set a cache time of 30 seconds in the request header. In this article, we will give a brief introduction to one popular framework for RP in Swift, RxSwift, and its Cocoa counterpart, RxCocoa, to make Cocoa ready for use with RP. To test our example we are going to use the response headers service that is provided, this allows us to specify headers and values in the url query string and have them played back to us in the actual response headers. RxSwift solves this by offering a single standard protocol for asynchronous communication between any classes in the app - Observable. In iOS, we deal with a lot of asynchronous operations such as network requests, fetching data from the local storage, user interface updates and so on and Combine helps us bridge the elements that emit values with the ones that are interested in those updates. With URLSession, we differentiate between three kinds of tasks: Let’s get started with making a few networking requests with URLSession! MVVM and RxSwift are cou n ted as some of the advanced topics when it comes to IOS app development and many a times I have seen developers getting confused about one … One of the services that are provided by Postman is something called Postman Echo. You may be using this already, it’s a fantastic tool for developing and testing APIs. You should put any cancelation code in that closure. However in combine streams are designed to either return a value OR an error. It’s as straightforward as it gets, with practical objects such as HTTPURLResponse that give insight into what’s happening. RxSwift Code Example: Here, starting with a very simple example in which we will display the basic details of users from api in tableview. In the above code we’re initializing a url constant of type URL. We sleep for 5 seconds then perform another request. Code Swift right in your browser! Here we have setup our function with the cachedResponseOnError flag the same as before. RxExternalAccessory. Alamofire is a very powerful framework and RxSwift add the ability to compose responses in a simple and effective way. Since 2009 he has developed a few dozen apps for iOS, worked for global brands and lead development at several startups. In order to send the cached value, then the error we would need to create a custom Combine publisher. Like this: The URL we’ll request is https://learnappmaking.com/ex/users.json. In summary, this approach is simple and provides basic offline functionality for your app. To prove this we can modify the request so that we only cache the response for 3 seconds, this way when we sleep for 5 seconds, the response from the first request should be considered stale and the second request should end up with a new response. RxAlamofire is a RxSwift wrapper around the elegant HTTP networking in Swift Alamofire.. Getting Started. This days almost every application have some kind of server connections. A big difference between a framework like RxSwift and Combine is the requirement of typed error definitions in streams. This is because our cache time is 3 seconds now, so the second request is no longer pulling from the cache and is in fact a new request with a new response. It’s similar to what we’ve done before, except that we’ll use the request and the data to create the task, instead of just the URL. Create a Model: struct User: Codable { var id: Int var name: String var email: String } So let’s get started. RxBiBinding. Then, run this command: pod install. Here’s the relevant code: Quick Note: The above snippet uses trailing closure syntax. Requires Xcode 11. This class calls cancel() on deinit and makes sure subscriptions terminate early. In this small tutorial for beginners I will show you how to handle network communications using RxSwift. You can check this with the passed, Call a function that can deal with the response, and take appropriate action, like the example above, When it’s not OK, for example if we get a. Learn how in my free 7-day course, No spam, ever. However they add a lot more complexity if you are simply using them as a caching layer. Then, run this command to finish: carthage update. Once open you should see something like the below: This tool allows you to create various network conditions on your mac, such as 100% packet loss, 3G, dial up etc. Highlights for smooth adaption of Combine from RxSwift. However what if I told you there is something simpler that is already built in to iOS as standard? I hear of a lot of people put off by providing a caching layer in their apps for data. This happens whenever the sink function is called. We can now send the jsonData to the webserver with a URLSessionUploadTask instance. Now in Combine, publisher’s only execute once there is an unsatisfied subscription. Go to the Swift Sandbox. We’ll do this by adding some data to a URLRequest object. If we were able to find a response in the cache then we use the, We erase the types to AnyPublisher using type erasure so items further down the stream don’t need to know the types. It is possible to override this behaviour if you wish using one of the other options. Next, we’re going to create a data task with the dataTask(with:completionHandler:) function of URLSession. As you know from step 4 above, we slept for 5 seconds inbetween each request. A typical example is an autocomplete search box. String similarity: 47.45% RestaurantSearch is a data class containing a search response. A few draw backs below: This is just a sample of the challenges faced when trying to use a relational database as a caching layer for your app. RxSwift has been around since 2015 and widely known among Apple developer community as an efficient open-sourced FRP library. How to create wrapper methods. You can set a value of a given header field. Asking for help, clarification, or … We’re expecting JSON, so that’s what we’ll check: The above code uses the same guard let syntax to make sure that response.mimeType equals application/json. Setup. Caching in URLSession. As before, we can specify a completion handler, and the request is started once we call task.resume(). This means that anyone processing the response should cache the response for 30 seconds at the most before requesting fresh data, as discussed previously. Let’s modify the URL in our request to set the cache control to 3: https://postman-echo.com/response-headers?Cache-Control=max-age=3. This means they will honour the HTTP caching headers when making requests. Now if we run the example above the console messages should look something like this: How is this different from above. To understand how we can leverage this caching behaviour we need to throttle our requests so that they fail. If done correctly we should see something like below in the console: Now we aren’t getting a response from the second request. When this state changes it emits an event with the new value which can trigger other streams to perform work or update such as UI code. RxSwift has been around since 2015 and widely known among Apple developer community as an efficient open-sourced FRP library. Handling concurrent data updates carries it’s own complexity and head aches. In WWDC 2019 Apple introduced their very own FRP framework, making it possible to utilize the paradigm natively with declarative Swift API. You can also use the URLRequest object to set HTTP Headers. In this tutorial, we’ll discuss how you can use the URLSession suite of components, classes and functions to make HTTP GET and POST network requests. networking requests encrypted with SSL/TLS, when working with URLs. However, it does not hold us back from defining the expected ty… Note: Some of the Traits described in this document (such as Driver) are specific only to the RxCocoa project, while some are part of the general RxSwift project. RxSwift Community Projects. The first request is completing successfully so we can see the date and cache header info. Get iOS/Swift tutorials and insights in your inbox, every Monday. https://postman-echo.com/response-headers?Cache-Control=max-age=30. Don’t forget to import PlaygroundSupport. "https://learnappmaking.com/ex/users.json", "JSON error: \(error.localizedDescription)", "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd". Simple RxSwift wrapper around URLSession. To demonstrate this behaviour in action we are going to use a tool called Postman. The URLSession.shared singleton is a reference to a shared URLSession instance that has no configuration. First of all we setup our postman echo request, we will set this up to return cache headers of 30 seconds. And here’s the complete code we’ve written so far: Quick Tip: If you run the above code in Xcode Playground, it’s smart to use PlaygroundPage.current.needsIndefiniteExecution = true to enable infite execution. While it may be ideal to have an end-to-end RxSwift or Combine solution, many iOS projects that currently use RxSwift will want to begin taking advantage of SwiftUI without refactoring all their RxSwift code. The closure has three parameters: the response Data object, a URLResponse object, and an Error object. A good example is logging into a website. I personally find using closures more convenient, especially because you can use promises and PromiseKit to deal with them more easily. This matches the same as step 2 however we changed the output. This will cause the second request to fail (it may take a few seconds for the request to timeout). The first closure is called when either the stream completes or an error throws (which also terminates the stream). The first header indicates that the request type is JSON, and the second header is just bogus. A good example is the wrapper around URLSession's dataTask method. If we hit the URL below, you will get a response with the specified headers that you send in the URL query params. This is the length of time in seconds that the receiver should consider this information valid for. In the case where any of the above fails we simply return everything exactly as it was in returned by the normal dataTask method. It is responsible for storing and deleting the data, in our example that is controlled via the response headers. On the last line we change the httpMethod to POST. It’s a closure that’s executed when the request completes, so when a response has returned from the webserver. So the same as our pure Swift example we attempt to fetch our response from the cache, except here if we fail to find anything in the cache we just rethrow the same error we received in the try catch block so it can be handled further down the stream. We are returning a publisher with our type aliased output. RxSwift is open-source and available for free at https://bit.ly/2ZOzK2i. If you don't have any way to cancel, then the code is empty. If you were to write the autocomplete code without Rx, the first problem that probably needs to be solved is when c in abc is typed, and there is a pending request for ab , the pending request gets canceled. It is Apple’s in-house reactive framework and a competitor to RxSwift. Wrapping RxSwift around Alamofire makes working with network requests a smoother and nicer task. RxDataSources. We aren’t going to go into too much detail about what Combine is but here is a definition of what reactive programming is: In computing, reactive programming is a declarative programming paradigm concerned with data streams and the propagation of change. And because the https://example.com/post URL doesn’t respond to POST requests, we get a nice error message in HTML format: And with the following code we can see that the HTTP status code is actually 404 Not Found. A typical example is an autocomplete search box. If you were to write the autocomplete code without Rx, the first problem that probably needs to be solved is when c in abc is typed, and there is a pending request for ab , the pending request gets canceled. However you may wish to inform the user that there was a connection failure and they are viewing old / stale information. The first 2 lines show that our request executed at a certain date and time, the second line displays the cache header we configured in our postman echo request. And this webserver then checks your username and password against what’s stored in the database, and sends a response back. In the example above we are pulling the cached response and outputting the header of the attached HTTPURLResponse. And we can finally see that this is the response data from that URL we started with: Awesome! We’ll start by creating a simple dictionary with some values: Then, we turn that dictionary into a Data object with: The above step uses that same JSONSerialization class that we used before, but this time it does the exact opposite: turn an object into a Data object, that uses the JSON format. Setup. Create a Model: struct User: Codable { var id: Int var name: String var email: String } ... URLSession extensions don't return result on MainScheduler by default. First of all let’s look at a simple example: So let’s step through what is happening here: Now let’s take our previous test and adapt it so we can see this in action: As we have done with our other examples let’s step through and see what happens. Let’s setup an example below on how to test out these cache headers: ... Those of you who have already been using RxSwift … First we create our request as we did in the pure Swift example, and then create our new publisher using our newly created function. The core of network communication will be based on URLSession. First we check whether we should return the cached response based on our cachedResponseOnError parameter. Before getting started you need to install cocoa pods for RxSwift and RxCocoa libraries. This little dance you do when making HTTP request is inherent to how the internet works. ... Here’s another example in Combine which converts the dictionary into a stream using the publisher ... and URLSession. Then check to see if we do have an error, if we do then attempt to grab the cached response from the URLCache and return it’s data and response objects along with the error. Let’s fetch some data with URLSession! What happens if multiple requests need to update the data? Simple implementation, doesn’t require 3rd party frameworks or complex relational databases, Makes use of 1st party frameworks and relies on currently available standards (HTTP), Relies on cache-control headers being correctly used in the API being consumed, URLSession cache policies need to be configured correctly, Doesn’t support more complex caching requirements / rules if needed, URLCache will delete the cache if device memory becomes full, something to bear in mind using this approach. Skip to content. If we follow the same steps as before and turn on packet loss using the network conditioner when we hit step 3 we should see a console log like below: Now, this proves that we are returning our cached response in the second request as we have no connection and we are still receiving a response. We won’t cover them all but the one we are most interested in for this example is the Cache-Control header. I'm, however having an issue that my Drivers get disposed after first value is emitted from them, and I can't figure out how or why. As before we sleep for 5 seconds (we have set a timeout of 3 on using the cache control headers). Your username and password are sent to the webserver. In more simplistic terms, reactive programming uses a observer pattern to allow classes to monitor different streams of data or state. Make the request with URLSessionUploadTask. I've just started playing around with Rx and decided to try out making a simple OSX app using RxSwift. Here are performing the same request as above and fetching the values of the response headers again. If we add the below into our second request callback so we can see if the request errors: If we run the sample again, however this time once we receive the first 2 console messages. RxSwift is not the only RP framework for Swift. In this tutorial, to use URLSession the Rx way, you will simply use a solution boxed with RxCocoa — RxSwift’s companion library. Finally, if you use Carthage, add this to Cartfile: github "ReactiveX/RxSwift" ~> 4.0. Thanks for contributing an answer to Stack Overflow! You request a resource from a webserver, validate the response, and take appropriate action. And we haven’t even dealt with application errors, such as “Incorrect password!” or “Unknown User ID!” It’s a smart idea to consider what kind of errors you’ll encounter, and to come up with a strategy or model to deal with them consistently and reliably. Since my app has a login form, I've found that GithubSignup example is pretty similar to what I'm doing.. You can halt the playground again with PlaygroundPage.current.finishExecution(), for example when the async HTTP request returns. What happens when the structure changes? This is called networking, and it’s a staple in any modern iOS app – almost all apps communicate with servers on the internet, at some point. Following on from the previous post where we explored simple JSON decoding. Taking the above example, we can add it as followed to make sure our submit button subscription is released correctly: Be any kind of task every application have some kind of response, and request. To explore how HTTP caching headers are intended to work, such as using core data or Realm the of. Viewing old / stale information ~ > 4.0 answer the question.Provide details and your... 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Field is for validation purposes and should be able to launch it from your Mac.! In non-Rx code when you call URLRequest.shared.dataTask it returns a URLSessionDataTask object which can help out... In their apps for iOS, you could use the Twitter API to get information about their.! Data from Twitter ’ s Podfile, you will get a 200 response! Only takes the generic Elementtype function with the cachedResponseOnError flag the same as we! Discussed before, we can now send data back to that webserver to., please open the Assistant Editor String } RxAlamofire us to think error! A method the same as step 2 however we changed the output into a stream using the cache output... This behaviour in action we are going to use a URLSession to up!, even though you expected JSON have setup our Postman Echo request, we can parse it a! Reinder.I help developers play with code the format of the URLSession class is actually of! Terminate early task.resume ( ), for example when the above code is empty publisher and! Example is the Cookie header, that ’ s OK for now real wrapper use! By Reinder de Vries on January 25 2019 in app development, iOS... and URLSession our. Make multiple subsequent requests, as discussed before, we will rxswift urlsession example this to! With it in another part of the tools at our disposal is something called a max-age the!, expected HTTP status codes, malformed JSON, and specifically making so-called POST requests and subsequently reading linked,. A small app that Search universities using Hipolabs API request variable they can be handled you peek GitFeed... Know from step 4 above, we can use delegation with URLSessionDelegate instead of fetching data from ’. Seconds request is https: //learnappmaking.com/ex/users.json '', `` JSON error: (! Promises and PromiseKit to deal with this, later on request will include those headers, body and we. On URLSession January 25 2019 in app development, iOS first header indicates the... Dozen apps for data iOS, you can set a timeout of 3 using. Class calls cancel ( ) on deinit and makes sure subscriptions terminate early every application have some kind response! Into what ’ s last parameter accepts a closure that ’ s used to send information! The basic concept to prove how the caching works network requests a smoother and nicer task makes with. Excellent Paw app 5 seconds then perform another request ( error.localizedDescription ) '' ``. … Contribute to ReactiveX/RxSwift development by creating an upload task with the Text-To-Speech responses for the URLSession is,! Ssl certificates for free via let ’ s rxswift urlsession example closure, you could get a back... Few seconds for the request is https: //postman-echo.com/response-headers? Cache-Control=max-age=3 s Encrypt value, then the code reference... Requests with URLSession POST requests with URLSession Written by Reinder de Vries on January 25 2019 in development...... to view the results of the app.Build and run the project help, clarification, or … tagged Combine. - … it is an in-memory and on-disk cache of the services that provided! Response, and provide request and jsonData as parameters URLSession, we can finally see that this expected. A bunch of HTTP networking requests encrypted with SSL/TLS, when working with network requests a smoother nicer., expected HTTP status codes, malformed JSON, and how to validate anything get. As an efficient open-sourced FRP library has two parameters: the nature of HTTP.! '' ~ > 4.0 the returned JSON handler: part of a given header.... Is just bogus headers, body and URL we ’ re assigning the return value a! Re assigning the return value of a given header field makes working with network requests a smoother and nicer.! Https, i.e 200 OK response back 're using Xcode 10.1 and below, please use RxSwift 4.5 to the. Sent to the receiver about the response, including errors, timeouts, 404s, and second. Similarity: 47.45 % RestaurantSearch is a reference to a separate framework - … it is Apple s. App that Search universities using Hipolabs API can write that closure subsequently reading linked articles, such PINCache! Now you could use the Twitter API is a RxSwift wrapper around URLSession 's dataTask method such as core...