Stutern Graduate Accelerator 0.7 Android development guest session - Introduction to Multithreading and Networking on Android

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Multithreading and Networking on Android Moyinoluwa Adeyemi + career advice

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Android Google Developer Expert

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Multithreading with RxJava

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Activity/Fragment (A/F) Service (S) Content Providers (CP) Broadcast Receivers (BR) UI/Main Thread Android Components

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A/F S Activity/Fragment (A/F) Service (S) Content Providers (CP) Broadcast Receivers (BR) BR CP A/F Message Queue Android Components

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A/F S BR CP A/F } 10ms } 13ms } 16ms } 15ms } 4ms 60fps

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A/F S BR CP A/F } 10ms } 13ms } 16ms } 20ms } 4ms Jank

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Common causes ● I/O operations (Network requests, Database Access)

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Common causes ● I/O operations (Network requests, Database Access) ● Long calculations (Image processing)

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The result https://developer.android.com/topic/performance/images/anr-example-framed.png

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Why bother? ⭐⭐⭐⭐⭐

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Why bother? ⭐⭐⭐⭐⭐

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Why bother? ⭐⭐⭐⭐⭐ ⏱⏱⏱⏱⏱

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Solution - Android AsyncTask

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AsyncTask ● Impossible to cancel a task

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AsyncTask ● Impossible to cancel a task ● Potential memory leaks

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Solution - Kotlin Coroutines

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Coroutines ● Beyond the scope of this talk, sadly…

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Solution - Open Source library

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RxJava “RxJava is a Java VM implementation of ReactiveX a library for composing asynchronous and event-based programs by using observable sequences.”

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RxJava Subscriber Observable subscriber.onNext()

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RxJava - Schedulers “Executes arbitrary blocks of code, possibly in the future”

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RxJava - Schedulers “Executes arbitrary blocks of code, possibly in the future” Schedulers + subscribeOn()

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RxJava - Schedulers “Executes arbitrary blocks of code, possibly in the future” Schedulers + subscribeOn() + observeOn()

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Schedulers.io() ● Unbounded pool of threads

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Schedulers.io() ● Unbounded pool of threads ● Threads are recycled

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Schedulers.io() ● Unbounded pool of threads ● Threads are recycled ● Used for I/O bound tasks

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Schedulers.io() ● Unbounded pool of threads ● Threads are recycled ● Used for I/O bound tasks ● Tasks take some time to complete

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Schedulers.computation() ● Bounded pool of threads

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Schedulers.computation() ● Bounded pool of threads ● Used for CPU intensive tasks

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Schedulers.computation() ● Bounded pool of threads ● Used for CPU intensive tasks ● Computation threads limited to the number of CPU cores

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Schedulers.trampoline() ● Schedules tasks in the same thread

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Schedulers.trampoline() ● Schedules tasks in the same thread ● Blocking, but waits for the current task to ﬁnish

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subscribeOn() ● Determines the thread which the source observable emits on

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subscribeOn() ● Determines the thread which the source observable emits on ● Works upstream - only the ﬁrst call counts

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subscribeOn() What thread will the source observable emit on? Observable.just("Hello", "World") .subscribeOn(Schedulers.io()) .subscribeOn(Schedulers.computation()) ...

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observeOn() ● Switches the current observable to the speciﬁed thread

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observeOn() ● Switches the current observable to the speciﬁed thread ● Works downstream - only the last call counts

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observeOn() What thread will the current observable be emitted on? Observable.just("Hello", "World") .subscribeOn(Schedulers.io()) .observeOn(Schedulers.computation()) .observeOn(AndroidSchedulers.mainThread()) ...

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TestScheduler “A special, non thread-safe scheduler for testing operators that require a scheduler without introducing real concurrency and allows manually advancing a virtual time.”

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TestScheduler - UseCase Observable.interval(ONE_SECOND, TimeUnit.SECONDS) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe({ ..... })

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TestScheduler - UseCase private val testScheduler = TestScheduler()

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private val testScheduler = TestScheduler() @Before fun setUp() { RxJavaPlugins.setComputationSchedulerHandler { testScheduler } } TestScheduler - UseCase

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@Test fun test_shouldReturnSuccess_whenRequestIsSuccessful() { viewModel.result.observeForever(observer) testScheduler.advanceTimeBy(1, TimeUnit.SECONDS) verify(observer).onChanged(...) } TestScheduler - UseCase

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AndroidSchedulers.mainThread() ● Available only in RxAndroid

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AndroidSchedulers.mainThread() ● Available only in RxAndroid ● Performs Android UI based work on the main thread

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Import RxJava in Gradle implementation "io.reactivex.rxjava2:rxjava:$rx_java2_version" implementation "io.reactivex.rxjava2:rxandroid:$rx_android_version"

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Networking with Retroﬁt

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Retroﬁt ● Open source library for making HTTP requests

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Retroﬁt ● Open source library for making HTTP requests ● Accepts an HTTP client

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Retroﬁt ● Open source library for making HTTP requests ● Accepts an HTTP client ● Accepts a Call Adapter factory

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Retroﬁt ● Open source library for making HTTP requests ● Accepts an HTTP client ● Accepts a Call Adapter factory ● Accepts a Converter factory

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Retrofit - Converters ● Gson: com.squareup.retrofit2:converter-gson ● Jackson: com.squareup.retrofit2:converter-jackson ● Moshi: com.squareup.retrofit2:converter-moshi ● Protobuf: com.squareup.retrofit2:converter-protobuf ● Wire: com.squareup.retrofit2:converter-wire ● Simple XML: com.squareup.retrofit2:converter-simplexml ● Scalars (primitives, boxed, and String): com.squareup.retrofit2:converter-scalars

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Retroﬁt + OkHttp val okHttpClient = OkHttpClient.Builder() .build()

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Retroﬁt + OkHttp Retrofit.Builder() .client(okHttpClient)

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Retroﬁt Retrofit.Builder() .client(okHttpClient) .baseUrl(BuildConfig.BASE_URL)

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Retroﬁt Retrofit.Builder() .client(okHttpClient) .baseUrl(BuildConfig.BASE_URL) .addConverterFactory(MoshiConverterFactory.create(moshi))

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Retroﬁt Retrofit.Builder() .client(okHttpClient) .baseUrl(BuildConfig.BASE_URL) .addConverterFactory(MoshiConverterFactory.create(moshi)) .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .build()

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Retroﬁt - Annotations GET POST PUT DELETE HEAD

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Retroﬁt - Interface https://demo.sga.org/latest?town=lagos interface DemoService { @GET("/latest") fun getLatestDemo(@Query("town") town: String): Observable }

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Retroﬁt - Interface https://demo.sga.org/latest?town=lagos interface DemoService { @GET("/latest") fun getLatestDemo(@Query("town") town: String): Observable } val demoService = retrofit.create(DemoService::class.java)

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Retroﬁt + RxJava (Multithreading) https://demo.sga.org/latest?town=lagos demoService.getLatestDemo("lagos") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread())

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Retroﬁt + RxJava (Error handling) https://demo.sga.org/latest?town=lagos demoService.getLatestDemo("lagos") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe({ demo -> ...}, { error -> ... })

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Import Retroﬁt in Gradle // moshi implementation "com.squareup.moshi:moshi-kotlin:$moshi_version" implementation "com.squareup.moshi:moshi-adapters:$moshi_version" // Retrofit implementation "com.squareup.retrofit2:retrofit:$retrofit_version" implementation "com.squareup.retrofit2:converter-moshi:$moshi_converter_version" implementation "com.squareup.retrofit2:adapter-rxjava2:$rx_java_adapter_version"

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Career Section

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What are employers looking for?

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What are employers looking for? ● Technical Experience suitable for the role

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What are employers looking for? ● Technical Experience suitable for the role ● “Soft” skills

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What are employers looking for? ● Technical Experience suitable for the role ● “Soft” skills ● Growth potential

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What are employers looking for? ● Technical Experience suitable for the role ● “Soft” skills ● Growth potential ● Bonus - Writing skills

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What are employers looking for? ● Technical Experience suitable for the role ● “Soft” skills ● Growth potential ● Bonus - Writing skills ● Bonus - Contributions to the community

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Building a career portfolio

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Building a career portfolio ● Contribute to an existing project

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Building a career portfolio ● Contribute to an existing project ● Upload code snippets or sample apps to Github

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Building a career portfolio ● Contribute to an existing project ● Upload code snippets or sample apps to Github ● Publish apps on Google Play

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Building a career portfolio ● Contribute to an existing project ● Upload code snippets or sample apps to Github ● Publish apps on Google Play ● Write technical articles

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Building a career portfolio ● Contribute to an existing project ● Upload code snippets or sample apps to Github ● Publish apps on Google Play ● Write technical articles ● Give talks

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How to ﬁnd opportunities

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How to ﬁnd opportunities ● Social media (LinkedIn, Twitter, StackOverﬂow Jobs)

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How to ﬁnd opportunities ● Social media (LinkedIn, Twitter, StackOverﬂow Jobs) ● Newsletters (Forloop, Android/Kotlin Weekly)

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How to ﬁnd opportunities ● Social media (LinkedIn, Twitter, StackOverﬂow Jobs) ● Newsletters (Forloop, Android/Kotlin Weekly) ● Job Search marketplace (Hired.com, Fiverr, Upwork)

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How to ﬁnd opportunities ● Social media (LinkedIn, Twitter, StackOverﬂow Jobs) ● Newsletters (Forloop, Android/Kotlin Weekly) ● Job Search marketplace (Hired.com, Fiverr, Upwork) ● Company Career pages

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Questions?

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Resources ● https://developer.android.com/training/articles/perf-anr ● http://hvasconcelos.github.io/articles/Oﬄoading-work-from-the- UI-Thread ● https://blog.gojekengineering.com/multi-threading-like-a-boss-in -android-with-rxjava-2-b8b7cf6eb5e2 ● https://square.github.io/retroﬁt/ ● Reactive Programming with RxJava - Tomasz Nurkiewicz

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Take home task

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Take home task Create a one page app with GitHub’s public REST API, listing all names of users in Lagos. The app should make use of both RxJava and Retroﬁt for networking. Make the network request on the io thread. For bonus points, use an Android App architecture and write tests.

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Thank you!