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

In this presentation, I introduced two programming concepts to beginner Android developers in the Stutern Graduate Accelerator 0.7 Android development track. I explored Multithreading and Networking on Android with RxJava and Retrofit.

I also shared some career advice based on my experience. It touched on topics such as figuring out what employers are looking out for, learning how to build a career portfolio as an Android developer and how to find job opportunities.

Transcript

1. Multithreading and Networking on Android Moyinoluwa Adeyemi + career advice
2. Android Google Developer Expert
3. Multithreading with RxJava
4. Activity/Fragment (A/F) Service (S) Content Providers (CP) Broadcast Receivers (BR) UI/Main Thread Android Components
5. A/F S Activity/Fragment (A/F) Service (S) Content Providers (CP) Broadcast Receivers (BR) BR CP A/F Message Queue Android Components
6. A/F S BR CP A/F } 10ms } 13ms } 16ms } 15ms } 4ms 60fps
7. A/F S BR CP A/F } 10ms } 13ms } 16ms } 20ms } 4ms Jank
8. Common causes • I/O operations (Network requests, Database Access)
9. Common causes • I/O operations (Network requests, Database Access) • Long calculations (Image processing)
10. The result https://developer.android.com/topic/performance/images/anr-example-framed.png
11. Why bother? ⭐⭐⭐⭐⭐
12. Why bother? ⭐⭐⭐⭐⭐
13. Why bother? ⭐⭐⭐⭐⭐ ⏱⏱⏱⏱⏱
14. Solution - Android AsyncTask
15. AsyncTask • Impossible to cancel a task
16. AsyncTask • Impossible to cancel a task • Potential memory leaks
17. Solution - Kotlin Coroutines
18. Coroutines • Beyond the scope of this talk, sadly…
19. Solution - Open Source library
20. RxJava “RxJava is a Java VM implementation of ReactiveX a library for composing asynchronous and event-based programs by using observable sequences.”
21. RxJava Subscriber Observable subscriber.onNext()
22. RxJava - Schedulers “Executes arbitrary blocks of code, possibly in the future”
23. RxJava - Schedulers “Executes arbitrary blocks of code, possibly in the future” Schedulers + subscribeOn()
24. RxJava - Schedulers “Executes arbitrary blocks of code, possibly in the future” Schedulers + subscribeOn() + observeOn()
25. Schedulers.io() • Unbounded pool of threads
26. Schedulers.io() • Unbounded pool of threads • Threads are recycled
27. Schedulers.io() • Unbounded pool of threads • Threads are recycled • Used for I/O bound tasks
28. Schedulers.io() • Unbounded pool of threads • Threads are recycled • Used for I/O bound tasks • Tasks take some time to complete
29. Schedulers.computation() • Bounded pool of threads
30. Schedulers.computation() • Bounded pool of threads • Used for CPU intensive tasks
31. Schedulers.computation() • Bounded pool of threads • Used for CPU intensive tasks • Computation threads limited to the number of CPU cores
32. Schedulers.trampoline() • Schedules tasks in the same thread
33. Schedulers.trampoline() • Schedules tasks in the same thread • Blocking, but waits for the current task to finish
34. subscribeOn() • Determines the thread which the source observable emits on
35. subscribeOn() • Determines the thread which the source observable emits on • Works upstream - only the first call counts
36. subscribeOn() What thread will the source observable emit on? Observable.just("Hello", "World") .subscribeOn(Schedulers.io()) .subscribeOn(Schedulers.computation()) ...
37. observeOn() • Switches the current observable to the specified thread
38. observeOn() • Switches the current observable to the specified thread • Works downstream - only the last call counts
39. observeOn() What thread will the current observable be emitted on? Observable.just("Hello", "World") .subscribeOn(Schedulers.io()) .observeOn(Schedulers.computation()) .observeOn(AndroidSchedulers.mainThread()) ...
40. 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.”
41. TestScheduler - UseCase Observable.interval(ONE_SECOND, TimeUnit.SECONDS) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe({ ..... })
42. TestScheduler - UseCase private val testScheduler = TestScheduler()
43. private val testScheduler = TestScheduler() @Before fun setUp() { RxJavaPlugins.setComputationSchedulerHandler { testScheduler } } TestScheduler - UseCase
44. @Test fun test_shouldReturnSuccess_whenRequestIsSuccessful() { viewModel.result.observeForever(observer) testScheduler.advanceTimeBy(1, TimeUnit.SECONDS) verify(observer).onChanged(...) } TestScheduler - UseCase
45. AndroidSchedulers.mainThread() • Available only in RxAndroid
46. AndroidSchedulers.mainThread() • Available only in RxAndroid • Performs Android UI based work on the main thread
47. Import RxJava in Gradle implementation "io.reactivex.rxjava2:rxjava:$rx_java2_version" implementation "io.reactivex.rxjava2:rxandroid:$rx_android_version"
48. Networking with Retrofit
49. Retrofit • Open source library for making HTTP requests
50. Retrofit • Open source library for making HTTP requests • Accepts an HTTP client
51. Retrofit • Open source library for making HTTP requests • Accepts an HTTP client • Accepts a Call Adapter factory
52. Retrofit • Open source library for making HTTP requests • Accepts an HTTP client • Accepts a Call Adapter factory • Accepts a Converter factory
53. 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
54. Retrofit + OkHttp val okHttpClient = OkHttpClient.Builder() .build()
55. Retrofit + OkHttp Retrofit.Builder() .client(okHttpClient)
56. Retrofit Retrofit.Builder() .client(okHttpClient) .baseUrl(BuildConfig.BASE_URL)
57. Retrofit Retrofit.Builder() .client(okHttpClient) .baseUrl(BuildConfig.BASE_URL) .addConverterFactory(MoshiConverterFactory.create(moshi))
58. Retrofit Retrofit.Builder() .client(okHttpClient) .baseUrl(BuildConfig.BASE_URL) .addConverterFactory(MoshiConverterFactory.create(moshi)) .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .build()
59. Retrofit - Annotations GET POST PUT DELETE HEAD
60. Retrofit - Interface https://demo.sga.org/latest?town=lagos interface DemoService { @GET("/latest") fun getLatestDemo(@Query("town") town: String): Observable<Demo> }
61. Retrofit - Interface https://demo.sga.org/latest?town=lagos interface DemoService { @GET("/latest") fun getLatestDemo(@Query("town") town: String): Observable<Demo> } val demoService = retrofit.create(DemoService::class.java)
62. Retrofit + RxJava (Multithreading) https://demo.sga.org/latest?town=lagos demoService.getLatestDemo("lagos") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread())
63. Retrofit + RxJava (Error handling) https://demo.sga.org/latest?town=lagos demoService.getLatestDemo("lagos") .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe({ demo -> ...}, { error -> ... })
64. 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"
65. Career Section
66. What are employers looking for?
67. What are employers looking for? • Technical Experience suitable for the role
68. What are employers looking for? • Technical Experience suitable for the role • “Soft” skills
69. What are employers looking for? • Technical Experience suitable for the role • “Soft” skills • Growth potential
70. What are employers looking for? • Technical Experience suitable for the role • “Soft” skills • Growth potential • Bonus - Writing skills
71. What are employers looking for? • Technical Experience suitable for the role • “Soft” skills • Growth potential • Bonus - Writing skills • Bonus - Contributions to the community
72. Building a career portfolio
73. Building a career portfolio • Contribute to an existing project
74. Building a career portfolio • Contribute to an existing project • Upload code snippets or sample apps to Github
75. Building a career portfolio • Contribute to an existing project • Upload code snippets or sample apps to Github • Publish apps on Google Play
76. 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
77. 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
78. How to find opportunities
79. How to find opportunities • Social media (LinkedIn, Twitter, StackOverflow Jobs)
80. How to find opportunities • Social media (LinkedIn, Twitter, StackOverflow Jobs) • Newsletters (Forloop, Android/Kotlin Weekly)
81. How to find opportunities • Social media (LinkedIn, Twitter, StackOverflow Jobs) • Newsletters (Forloop, Android/Kotlin Weekly) • Job Search marketplace (Hired.com, Fiverr, Upwork)
82. 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
83. 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 • Employee referrals
84. Questions?
85. 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
86. Take home task
87. 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.
88. Thank you!