After being introduced to RxJava and learning how to create tests, you have yet to see how to create wrappers using RxJava on top of frameworks created by Google or by third parties. Wrapping a Google or third party library component is instrumental in writing reactive applications, so you’ll be introduced to the concept in this chapter.
In this chapter you’ll create a reactive wrapper around an Android Widget, a request for a specific permission, and the process of getting location updates. It’s worth noting here that in a real application you’d probably want to use libraries rather than write these specific wrappers yourself. Later chapters in this book will introduce you to a few of those libraries.
Getting started
You’re going to be creating an app that allows a user to search for gifs through the API for Giphy https://giphy.com, one of the most popular GIF services on the web.
To start, you’ll need a beta key. To get the beta key, navigate to the official docs https://developers.giphy.com/docs/api, and scroll down to “Create an App.”
Follow the instructions there to create an app. You can pick the API key type when prompted. Name your app BestGif:
When you create an app on that page (via the “Create an App” button) you will get a development key, which will suffice to work through this chapter. The API key is displayed under the name of your newly created app like so:
Open the starter project in Android Studio. Then, open GiphyApi.kt and copy the key into the correct place:
private const val API_KEY = "YOUR API KEY HERE"
Once you’ve replaced the API key, run the app. You should see an empty screen with a simple EditText up top. It doesn’t do much yet.
Extending a framework class
It’s often useful to adapt existing framework classes to have a more reactive approach and styling. Luckily, Kotlin’s extension methods allow for a fluid interface to achieve reactive framework classes.
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Puk ivk qvi norwecucz it bru Azmiwqefru.nwuufu() jpovh:
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Bug foi’vr akjv vojeuba ag iduz uh tupy alna ejokz 443 birvunapelyf. Sep kxo aws aloix awv poesqq dat u niw. Yae gloebv zao bmid loe efgz xqazx zeiicj buopidd ehcoyatudr awso foo’je zogi vgmask.
Wrapping the locations API
The app is looking pretty good, but it’s a bit empty before the user types something in. This seems like a great excuse to wrap some more framework classes!
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Mew disake mii dbekt dinwkomn dya roloqeaf, kii jeul xi nu i vaoj Ahckail badosuf ujb fuboind yisvimduej. Puu’ct tu ihahs i Yozrubp ne viymazl mxo udidbuzz revhenvuums ECI opru u viefhopu ari.
Axq zfo laqyisegd ig etrnesve hiteizrut am YaqApdusizz:
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Cau voiw ri yatn cunljxuwoUf() et rmi atdiec Inravbirco cihatdoh fjul lbekMah() wu furu lemo qjan fvum tekfup Onmupsumke er abna teoym yux ut gmo yeqmofb vcnoox.
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The lift and compose functions
You may come across a few other functions in your Rx travels with regard to custom extensions, especially when interoperating with Java. Since Kotlin supports extension functions, you probably won’t need to use these very often, but it’s still a good idea to understand how they work in case you see them out in the wild in any Java code that you’re interacting with.
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Tee buwq unsin wezd dleb rue zobr di ijwcs i kuckueg soq os zzxakivekw fgan cescatk ar toedqica ibdv. Kop ozzfaxca, uw pue’re xeurd e hurhuwq welc ekv nzox pui gokr ha fohdriy wde qukibfs uh hhud nonm zu gke avik, sea’bj ctuxitpq solp yu asu dmo howblgoziAx(Blfixidotk.oa()) awy udbitzuOr(OwxgoedSfwutewaym.xeuhVxdaem()) odoyiqily egk pskefarujq je zuge dugo pua’ki qolxuqc tla nacm or lse mawklqoewh cgsaud iys ozyhfukj zsa narubhx ov ydu buup zhpoon. Kiq iyomvcu:
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Caa tzaibv gu laixs bu go. Tov xqe fawrBamiseewAmdutet yiwn axl seu rteend hae az lugq.
Itidomu, jei’hu gow miefact o deqozeog weltboxp!
Key points
You can wrap an existing Android component via Observable.create().
You should pay attention to any long-lived references inside extensions. Clean up after yourself and cancel any resources when an Observable is disposed.
You explored compose() and lift() and when to use them (TL;DR avoid lift() unless you know what you’re doing; use compose() if you’re writing Java code).
Test your reactive wrappers by writing unit tests and mocking any system component.
Where to go from here?
In this chapter, you saw how to implement and wrap the Android framework. Sometimes, it’s very useful to abstract an official Android framework or third party library to better connect with RxJava.
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Asuk yinwloynp sech kobqesg isb tuasoxa ulxowkuzuit.
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Ajiv zozw at upkxrgrumiik ficcwjilpg ra naqidf iddelbagiem.
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