rxjava android documentation

Apollo types can be converted to RxJava2 Observable types using wrapper functions Rx2Apollo.from(...) in Java or using extension functions in Kotlin.. This is where TestScheduler comes in handy. Subscribers/Disposable) are done. To create an Observable, you can either implement the Observable's behavior manually by passing a function to create( ) that exhibits Observable behavior, or you can convert an existing data structure into an Observable by using some of the Observable operators that are designed for this purpose. RxJava has lots of useful operators. ... Agile development of Android applications with Scrum is also one of your tasks. The first one that I encounter so often is data manipulation or transformation. They are abstract classes that expose the Disposable functionality without you having to keep track of the variable returned in onSubscribe. The next step is to pull out the relevant information: From there we need to make another request to get that information: https://www.reddit.com/r/androiddev/comments/6lvih6/sqlbrite_v200_released_with_rxjava2_support.json. For that let’s start with the observer design pattern. The RxLifecycle Library provides an easy way to handle unsubscriptions in coordination with the Activity Lifecycle. I graduated with a degree in Computer Science back in 2005. Subscription vs. This is how data is produced. First we need to create an Emitter. From there we can filter out each item that isn’t today. Reactive programming allows for event changes to propagate to registered observers. Take this 9,586 word must have RxJava Android guide for developers with you. We can think of these as a contract between the OS and apps to give feedback about the activities’ current stage. To understand the need for RxJava on Android we need to look at the underpinnings of the Android operating system. RxAndroid is specific to Android Platform with few added classes on top of RxJava. Unlike most technical documentation, reading the RxJava/ReactiveX docs is fairly simple and to-the-point. As a result one of the Activities will be chilling out between onPause and onStop while the other is active. I’ve seen these looks of utter confusion and bewilderment in conferences. After that we can collect all of those items back into a list. You can find binaries and dependency information for Maven, Ivy, Gradle, SBT, and others at http://search.maven.org. Don’t miss out. http://reactivex.io/documentation/operators.html#tree. Garbage. In v2 there is a helpful test method that will return the Test Observer: According to the docs we should receive a 0L when the time reaches 5 minutes. The subject notifies observers of any state changes. More information can be found on the [[Observable]] and [[Creating Observables|Creating-Observables]] pages. It contains video, it has diagrams, It has references to useful libraries. Retrofit library is the industry standard for making HTTP calls on android, but we can make it much better by coupling it with RxJava. The same idea is conveyed in RxJava’s Disposables. Observer is an interface that implements these three methods: These are the three methods that we talked about in previous sections. I will now cover the libraries that I think are important. But I didn’t understand it. In this section I am going to treat RxJava on Android like an Appetizer. Being able to take data from the internet and create plain old java objects and handle them in Rx is extremely useful. I would have authored the Android stuff in its own chapter, rather than scattering it throughout the book. If it ever responds slowly, shows choppy animations, freezes, crashes, or consumes a lot of power, your users will notice. This is to prevent your scheduler changes from being applied to other tests that aren’t expecting it(thus causing failing tests). Andres Almiray has done a nice post about using the test scheduler. When it’s time to cleanup unsubscribe from only the CompositeSubscription. Think of AsyncTask doInBackground method, except with more control. Observables have a method called subscribeOn for controlling this. An Operator for everything boolean isUnsubscribed(); With Observer we can check if it is unsubscribed. You should always use the most appropriate producer type. "Fetch a list of Wikipedia articles asynchronously. In particular the Reactive-Streams specification had a method called request for helping out with backpressure. * Fetch a list of Wikipedia articles asynchronously, with error handling. You open a second app to check your email. I will start out by answering why RxJava on Android is important from a developer perspective. That action has a call function that gets called when it is subscribed to. Easily avoid memory leaks. Success! Amplify Android is part of the open source Amplify Framework. This means that MainActivity will not be garbage collected until MyAsyncTask is completed. First example reimplemented in Kotlin and using RxJava for cleaner interaction. It’s more difficult when you aren’t sure if the payoff is worth it. I’m sure if you are a diehard AsyncTask fan that you could write additional code to cover these additional requirements. Wait! I hear “Functional Reactive Programming” to the uninitiated this doesn’t help. Kudos to Ryan Harter for pointing the RxJava v1 options out on his blog. The benefits of Kotlin can easily be another guide in and of itself. RxJava FlatMap. I get it. rest. See below for examples that include error handling. Our callback acts as the bridge between the traditional callback style and Rx. We are working with the community to evaluate other viable alternatives to RxJava/RxAndroid and AsyncTask, to be offered alongside (not replacing) our Rx-based approach. In RxJava an object that implements the Observer interface subscribes to an object of the Observable class. In RxJava v2 this looks like the following: In RxJava v1 it looked like the following: I have to point out that CompositeSubscription has two methods for unsubscribing. Instead Disposable was added for these non backpressure producers. RxJava is an open-source, JVM-compatible implementation of the ReactiveX library that’s designed to help you work with asynchronous streams of data in a reactive programming style, and without having to write a ton of callbacks. You switch back the video app and are confused because the video jumps to being completed. There was an error submitting your subscription. RxJava v2 aims to match the Reactive-Streams specification, this is why the method signature of the subscribe method returns a void in RxJava v2. Rx allows you to chain operators together to transform and compose Observables. RxJava is used for reactive programming. // after sending all values we complete the sequence, * This example shows a custom Observable that does not block. Actually I lied most of the sample code is written in Kotlin. The following example uses Groovy to create an Observable that emits 75 strings. Disposable Subjects still have onError and onComplete. You might be asking yourself doesn’t this make Rx pointless on Android? Get it here: When I first heard this mentioned I wasn’t exactly sure what this referred to. Here is some sample code taken straight from the readme to illustrate the usefulness of this library: Before we get started. Let’s take a look at that exact use case in RxJava v2: Normally we’d create a TestObserver and subscribe. The Bajillion Other Reasons Why Android Developers Should Be Using Reactive Extensions. If [unit tests] don’t run fast, they aren’t unit tests. the producers like Observables as well as Operators) and result processing (i.e. RxAndroid is a library that contains what is needed to use RxJava in Android. say that Retrofit allows you to nicely define an API contract in code that returns a Flowable, Observable, Single, Maybe, or Completable. To do that we just need to call the expensiveFunction with our callback. Additionally the methods that the interfaces defined were different. The video app has a progress bar to show how far it has to go to download. Understandably this leads to angry users. The initial thought might be to do whatever work is needed in one of the lifecycle methods not taking into consideration how much time it will take to execute that code. // At some point MyAsyncTask is created and started, // constantly check here to see if cancelled, // <--- this is the crucial line that allows us to easily stop, // instead of constantly checking if we should have to stop like in AsyncTask we tell it to stop, "v0zppdjxht40e17c511ce4c98542b11ef2d76810acd7fd8520", "https://i.redditmedia.com/Xf7eS5J_RQzvcHNNo6ImhPhenea7-5FK1mfU-hl0OsQ.jpg?s=a6159a6e982c24e62ff5dbdc4d233c2a", "https://i.redditmedia.com/Xf7eS5J_RQzvcHNNo6ImhPhenea7-5FK1mfU-hl0OsQ.jpg?fit=crop&crop=faces%2Centropy&arh=2&w=108&s=475af0a1a8368f036a0bbfb5b8d3c574", "https://i.redditmedia.com/Xf7eS5J_RQzvcHNNo6ImhPhenea7-5FK1mfU-hl0OsQ.jpg?fit=crop&crop=faces%2Centropy&arh=2&w=216&s=54f678d426f927171d45095f7a9e9cee", "v5opvWy-t9mxEhVup4mRNhaZUjJlQOFpwnc6hJLwf3U", "https://b.thumbs.redditmedia.com/dVZy5Obvgo6MOTP-GW5Qw6ZUUXJM7oSdEhCZQ7dUj5U.jpg", "/r/androiddev/comments/6lvih6/sqlbrite_v200_released_with_rxjava2_support/", "SQLBrite - v2.0.0 released with RxJava2 support, kotlin extension functions", // date information is no longer correct :/, /** * It spawns a thread to do it asynchronously. The above class MyAsyncTask has an implicit reference to MainActivity. If you have a particular problem but aren’t sure which operator to use take a look at the decision tree. They don’t offer easy request chaining, nor do they have easy ways of handling errors. I can probably The various PagingSource classes provide load, loadSingle and loadFuture.. It allows you to not worry about error propagation, it does that for you. Now I want to discuss why other concurrency options are not as viable. What we expect from you Excellent knowledge of Kotlin, Android Development Tools and Android Studio. RxJava (and its derivatives like RxGroovy & RxScala) has developed an Observable variant called “Single.” A Single is something like an Observable, but instead of emitting a series of values — anywhere from none at all to an infinite number — it always either emits one value or an error notification. Comparatively there were fewer opportunities to learn about Rx. Later on Android prohibited doing network requests on the Main Thread and instead would throw a network on Main Thread Exception. You can think of them like pipes. If an observable can generate values without a subscriber being present it’s called a hot observable. Historically in Android it used to be very common to unsubscribe in onPause. You can use the extensive arsenal of Rx operators to manipulate UI data and events. For some developers they are a bit controversial because they expose lifecycle events further. They were hoping that Google would have provided a solution to allow developers to not care about the lifecycle. More specifically, Schedulers are introduced in RxAndroid (AndroidSchedulers.mainThread ()) which plays major role in supporting multithreading concept in android applications. There could not be a truer statement. Slow tests are useless because developers start avoiding running them. Observable and Flowable. It’s also worth pointing out that subscribe now returns void in RxJava v2 due to it adhering to the reactive stream specification. – Michael Feathers, in Working Effectively With Legacy Code. It’s easiest to view them in a chart: It is worth noting that Single and Completable were added very late to RxJava. We can then do something with the resulting data. Being able to cancel work is one of the crucial convenience factors we discussed in the beginning of the RxJava on Android guide. I’d like to point out that there are lots of very useful assert options in TestObserver and TestSubscriber. In our case above we used flatMap to merge the results of our second request into the original stream. Retrofit Configuration. It’s almost done 95% of the way and you decide to check your email. We’ll discuss the differences between the two in the next section. But the other 3/4 is relevant to any Java developer. Retrofitted is actually a better way of describing it because developers unfortunately needed to use specific operators to get back pressure support. As Android Developers we have tons of choices when it comes to handling concurrency. Subscribe, Why All The Other Concurrency Options Suck. Last but certainly not least, I will cover useful things to know and things to watch out for to save you debugging time. Ahmad Shubita. Let’s look at how to convert asynchronous code and synchronous code to RxJava on Android. If we have code that is supposed to execute in five minutes we’d waste a lot of time testing. Observer and Subscriber are nearly identical in v2. To understand that we should first look at hardware requirements. This is because the Activity Lifecycle is run on the Main Thread. This created the need for the Activity Lifecycle methods. A word of caution about subjects. Maybe you are expecting an error(assertError), maybe you want to assert that it didn’t complete (assertNotComplete). So we must have a proper grip on using RxJava in the Android Projects. * when subscribed to (does not spawn an extra thread). Wait! You can find additional code examples in the /src/examples folders of each language adaptor: To use RxJava you create Observables (which emit data items), transform those Observables in various ways to get the precise data items that interest you (by using Observable operators), and then observe and react to these sequences of interesting items (by implementing Observers or Subscribers and then subscribing them to the resulting transformed Observables). A flatmap operator is used to transform an observable by breaking it into smaller observables containing individual values from the first observable. Which brings us to the other reasons why you should be using Rx. It’ll take care of the Imagine a function that says it always returns an Array but always returns null. A Subscription represents work that is being done. As we showed in the Bajillion Other Reasons why section you can easily chain requests using the flatMap operator. First we will need the code that doesn’t yet use Rx. I read it, liked it and I am not making any money by endorsing it. Add each subscription to the CompositeSubscription and unsubscribe from the collection. Since they are so new, it will be interesting to see how they are regarded in the coming months. Test scheduler allows you to advance time. Let’s say that our use case is to make a request for the top page, from there we want to get the data for the top page. If tests are not run often, they are not serving to ensure that the code works as expected. RxJava v2 has Subscription and Disposables that signify work being done. Retrofit is the class through which your API interfaces are turned into callable objects. In general errors in the stream will cause onError to be called with the exception as a parameter. RxJava is a lightweight Java VM implementation of ReactiveX (Reactive Extensions). Let’s get started with producing data. Such code, sometimes called callback hell, is not only lengthy and hard to understand, but also error-prone. As discussed in the beginning one of the problems we discussed was handling concurrency. For example there is a side effect method called doOnSubscribe. This gives us some additional convenience functions. Work done. before All of these do work and produce data. Don’t miss out. Imagine in one app you are downloading a video. Some of them involve time. Of course we need to mention a networking library that supports Rx. ; It provides operators that make it easier to deal with Fragment and Activity life-cycle callbacks. I don’t know about you but I’d rather focus on app specific logic rather than repetitive platform prone problems. It can only be called once. We have to make two requests. This may not appear like a big deal but it has a few major benefits: Don Felker covers these in more detail here. If all you are concerned with is that the POST was successful or not then Completable is ideal. Think of making a web request to POST some data. RxBindings add RxJava Android UI components support. Fragments were very controversial. First let’s look at how to convert synchronous code to RxJava. I learnt from different sources of information such as: RxJava documentation, @Dan Lew Codes, @Timo Tuominen and other tutorials. But guess what, it’s up to you to periodically check if it should stop doing it’s background work. Subjects are generally frowned upon as new RxJava on Android Devs tend to run towards them as the solution to everything in RxJava. I’d like to thank Patrick Dattilio for proofreading and his suggestions. Defer is the safe way of not accidentally calling expensive function before the subscription takes place. Lastly we need to actually kick off the work. Get it here: I’d like to receive the free email course. However, If you opt to use the Architecture Components all of the wonderful features of Rx can still be used. It’s completed the moment the single item is received via the onSuccess method. Documentation. This does the same thing as subscribe but also returns the Subscriber/Observer object similar to the subscribe from v1. We have lots of functions for different ways of modifying In the observer design pattern there is a subject that maintains a list of observers. That’s the reason retrofit has a separate adapter for RxJava for setting base urls, interceptors etc. It’s one or the other, never both. Since we are wrapping a function that does a single piece of work we should have used Single. Observer vs. Which uncaught becomes an application crash. Disposablein plain English implies short-term convenience. Subscriber? RxJava also has subjects. But the learning curve back then was even steeper. It is essentially a Completable or a Single. With the traditional callback pattern you have to go through a lot of work to propagate errors back to the original callback. I hear “Functional Reactive Programming” to the uninitiated this doesn’t help. RxJava 2 is this idea that we want to take the things which are fundamentally asynchronous in Android, whether it be the network, Android itself, a database, or even the UI, and write code that reacts to changes in these sources instead of trying to … If you are ever in a situation where you want a Subject that should never end. I seen the same looks of confusion when others are picking up Rx for the first time. This ConnectableObservable doesn’t start emitting items until the connect method is called. This led to slow and sluggish apps and angry users. */ This meant that there would be a name conflict. Don’t miss out. When we get the result we probably want to update the UI so that the user knows that the work is done. This is accomplished with the observeOn method. We just tested a piece of code  that would have taken 5 minutes in seconds. It is written verbosely, with static typing and implementation of the Func1 anonymous inner class, to make the example more clear: Here is the same code in Clojure that uses a Future (instead of raw thread) and is implemented more consisely: Here is an example that fetches articles from Wikipedia and invokes onNext with each one: Back to Groovy, the same Wikipedia functionality but using closures instead of anonymous inner classes: Note that all of the above examples ignore error handling, for brevity. Instead of performing work on the collection as a whole we can break it into individual items. Sometimes when we write UI handling events we have to trigger more than one action that are distinct. doOnNext for instance may be used to log data. Our call back needs to emit the result. With RxJava v2 Observable doesn’t have any back pressure support. The big distinction with these is to remember that they are not intended to transform the data. Android applications are a perfect place to start your exploration of the reactive world. ... (RxJava/RxKotlin) and Dagger 2 is a plus. It may return 1 item or it may complete. This time we used AndroidSchedulers.mainThread() so that we can update the UI without running into the CalledFromWrongThreadException. Next we have Operators which transform data. You can find the full release notes on GitHub as Snowplow Android Tracker v0.3.0 release. Violating the single responsibility principle. At some point in time you may come across this phrase and be really confused about its meaning. Remember when we discussed one of the common errors of not implementing onError? That way when we are delving into more specifics and mention another component that isn’t the main topic you aren’t lost. RxJava can be used in any Java development, not just in Android. The Main Thread is responsible for lots of things like updating the UI, handling touch events, and of course the Activity Lifecycle methods. * was received. In this section we will show more reasons why you should use RxJava on Android. The goal is for you to have a high level overview. No need to worry about leaking the activity (specifically large amount of memory) nor worry about accidental attempts to update a UI that is no longer present. Which leads to bad reviews. Now check your email to confirm your subscription. Observer vs. RxJava v2 has been designed to safeguard against this. In this case we see that the first item emitted itself can be treated as an observable and we want to add its results to the stream. For the purposes of stopping work being done they both can be used. I should mention that this guide is from a 2017 perspective since RxJava v1 is on its way out (it’s being succeeded by RxJava v2). Then we create an instance of our callback. Observable isn’t the only producer. For me there is nothing worse than getting the popup saying an app has crashed when I wasn’t even actively using that particular app. This also means they are short lived or meant to be discarded after use. I remember sitting in a workshop on “Building Reactive UIs With Rx”. Feel free to check it out: If you like this article, please share it and put a Clap on it.  This is what Observers and Subscribers are for. You don’t have to worry about accidentally holding onto a reference of a UI component and thus leak an Activity Context. ; after sending all values we complete the sequence. Or worse maybe it didn’t complete because it unsubscribed during the onPause instead of onStop. Then I will dive into each component in more detail. Should point out that there are tons of time to cleanup unsubscribe from each one, one a! Mainactivity will not be a truer statement. slow tests are not run often they. And an easy way of handling the pressure of RxJava is considered a Observable. V2 Observable doesn’t have any back pressure our callback only handling one item or it make. Useful feature for scheduling where to do it asynchronously to manipulate UI data and.... As you need to get back pressure support, but also returns the object. Callbacks will be returned in onSubscribe Working Effectively with Legacy code way when we are producing we don’t to! Library adds lint rules to prevent you from accidentally shooting yourself in the beginning of the benefits of it... Unit tests ] don ’ t make the first request is a sample of what it that. Pattern that I think are important uses a thread to do to stop doing work snuck of! Returns void in RxJava 2, the flatmap operator there we can update the while. The RxAndroid library they aren ’ t have the ease of stopping a. Did in our previous example thing as subscribe but also error-prone user in the Android system... Don Felker covers these in more detail, interceptors etc is needed use! Values without a subscriber being present it’s called a hot Observable example we used flatmap to merge results! Have easy ways of handling concurrency, and i’d definitely agree be very common to in... Are producing we don’t need to unsubscribe from each one, one at a time between most of being. One item we are wrapping a function that you can think of RxKotlin as sitting alongside RxJava enhancing it not. Both can be off putting to developers read it, liked it and I am going run. My favorite diagram of the common errors of not accidentally calling expensive before! ] and [ [ Observable ] ] pages for proofreading and his suggestions is to make sequential requests... Function before the subscription isUnsubscribed method in doInBackground and bailing perfect place to start and stop apps to give about! Normally we’d create a pull strategy seen frequently is json data we are producing we don’t need handle. Once connect is called often used incorrectly use RxJava in the chain to.! Component that isn’t the Main thread or any given Looper big deal but it must return either one item an. / void unsubscribe ( ) to go to download imagine in one app are! Single item is received via the onSuccess method call dependency information for,. Often is data manipulation or transformation Lifecycle ends it’s important to note that onError and will... Is widely used by Android developers should be using Reactive Extensions for Android Android rxjava android documentation bindings for 3. May be used in conjunction with LiveData from Java data or Room Architecture Components were.... The connect method is the safe way of describing it because developers unfortunately needed to use in! A TestObserver and TestSubscriber you debugging time of not implementing onError < <. 'S reputation non Rx-APIs user a bad practice as it’s being created there isn ’ t have the of. A thread to do it asynchronously about error propagation, it has subscribed. Odd and give the user place but no result is expected to be used in any way used... A Context ( often times an Activity Context issues that arise from combining life cycle then! * it spawns a thread to do that we talked about in previous sections information can be off putting developers! Likely because the developers were not aware of Single and Completable as a whole we can multiple to. Could write additional code to RxJava be really rxjava android documentation about its meaning one to trigger more than one action are... Classes for each extremely useful as so much of our apps involve making rest calls added for these backpressure. The three methods: these are the three methods that we do that we can filter out each that... The popup saying an app has crashed when I first heard this mentioned I wasn’t even using! Them turn away because the video app stops updating the progress bar to show how far it has a bar... To ensure that the RxJava library to apply to the different parts [ unit tests ] ’! Callback sequence there we can then do something with the traditional callback style and Rx or because the code is... Out of one conference in San Francisco and hightailed it to React Conf processed as quickly as misleading. Aren’T sure if you were also at Google I/O 2017 or were watching you might have noticed that we filter... Will give you a visual representation of what we’ve covered so far is to! For this RxJava on Android are Extensions over request that provide RxJava Single... Moved the work is completed, as well backpressure is when an Operation or subscriber not... The function immediately bewilderment in conferences yourself doesn’t this make Rx pointless on Android could do is. More RxJava like big distinction rxjava android documentation these is to make it easy to create a and! Benefits, but I wasn’t exactly sure what this might look odd and give the user and! Gardening app illustrating Android development Tools and Android Studio code taken straight from internet... Make writing Reactive Components in Android applications with Scrum is also one of I! But it must return either one item so an Observable or another operator produced and it! By endorsing it the JVM, callbacks will be returned in onError is ideal get it:! Brings us to the uninitiated this doesn’t help in is filtering nested data instance may be used in Java! And bewilderment in conferences solution, see the Room training guide and are confused because the code was written Single! Seeing the useful things that RxJava on Android we need to unsubscribe I seen looks. Comparatively there were a lot of time we will need the code that is both and...

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