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
   

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2. Android Google
   Developer Expert
   

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3. Multithreading
   with RxJava
   

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

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

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

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

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

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

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11. Why bother?
    ⭐⭐⭐⭐⭐
    

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12. Why bother?
    ⭐⭐⭐⭐⭐
    
    

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13. Why bother?
    ⭐⭐⭐⭐⭐
    
    ⏱⏱⏱⏱⏱
    

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14. Solution - Android
    AsyncTask
    

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15. AsyncTask
    ● Impossible to cancel a task
    

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16. AsyncTask
    ● Impossible to cancel a task
    ● Potential memory leaks
    

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17. Solution - Kotlin
    Coroutines
    

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18. Coroutines
    ● Beyond the scope of this talk, sadly…
    

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19. Solution - Open Source library
    

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20. 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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21. RxJava
    Subscriber Observable
    subscriber.onNext()
    

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

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

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

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25. Schedulers.io()
    ● Unbounded pool of threads
    

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

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

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28. 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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29. Schedulers.computation()
    ● Bounded pool of threads
    

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

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

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

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

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

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

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

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

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

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39. 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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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.”
    

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

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42. TestScheduler - UseCase
    private val testScheduler = TestScheduler()
    

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

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

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45. AndroidSchedulers.mainThread()
    ● Available only in RxAndroid
    

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

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

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48. Networking with
    Retrofit
    

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49. Retrofit
    ● Open source library for making HTTP requests
    

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

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

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52. 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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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
    

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

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

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

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

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

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59. Retrofit - Annotations
    GET
    POST
    PUT
    DELETE
    HEAD
    

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

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

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63. 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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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"
    

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65. Career Section
    

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66. What are employers
    looking for?
    

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

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

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

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

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71. 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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72. Building a career
    portfolio
    

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73. Building a career portfolio
    ● Contribute to an existing project
    

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

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75. 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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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
    

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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
    

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78. How to find
    opportunities
    

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

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

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81. 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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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
    

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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
    

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84. Questions?
    

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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
    

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86. Take home task
    

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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.
    

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88. Thank you!
    

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