Reactive Live Coding

Presentation covering basics of Reactive Programming, RxJava and RxAndroid prepared for GDG DevFest 2015 in Warsaw, Poland (http://devfest.pl). It was also presented during Gliwice Software Barcamp in January 2016 and Silesian Java Users Group (SJUG) meeting in Katowice in February 2016. Source code of the sample Android app shown and partially coded during the presentation is available at: https://github.com/pwittchen/guitar-browser

Transcript

1. Reactive Live Coding
   Piotr Wittchen
   

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2. What is the presentation plan?
   ● Quick introduction to RxJava
   ● Some coding
   ● Summary
   

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3. What is Reactive Programming?
   

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4. ArrayList list = Arrays.asList( );
   Imperative Programming
   1 2 3 4 5 6
   for(Integer n : list) {
   operate(n);
   }
   for(Integer n : list) {
   if(n % 2 == 0) {
   operate(n);
   }
   }
   Data is pulled from its source
   

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5. Reactive Programming
   1 2 3 4 5 6
   2 4 6
   filter(n % 2 == 0)
   Data is pushed to the stream
   

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6. Observable.just( )
   .filter(i -> i % 2 == 0)
   .subscribe(i -> {
   });4
   Reactive Programming
   1 2 3 4 5 6
   2 4 6
   

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7. Reactive Programming
   Observable.just(1,2,3,4,5,6)
   .filter(i -> i % 2 == 0)
   .subscribe(item -> System.out.println(item));
   

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8. Reactive Programming
   Observable.just(1,2,3,4,5,6)
   .filter(new Func1() {
   @Override public Boolean call(Integer i) {
   return i % 2;
   }
   })
   .subscribe(new Action1() {
   @Override public void call(Integer item) {
   System.out.println(item);
   }
   });
   

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9. Important structures of RxJava
   public class Observable {
   Subscription subscribe();
   // has maaany methods for stream operations
   ...
   }
   public class Subscriber
   implements Observer, Subscription {
   ...
   }
   public interface Observer {
   void onCompleted();
   void onError(Throwable e);
   void onNext(T t);
   }
   public interface Subscription {
   void unsubscribe();
   boolean isUnsubscribed();
   }
   

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10. Multi-threading with RxJava
    Observable.just(1,2,3,4,5,6)
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(new Action1() {
    @Override public void call(Integer item) {
    System.out.println(item);
    }
    });
    order of called methods matters
    

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11. Let’s code!
    

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12. Everything can be a stream! Observable is an abstraction!
    ● HTTP responses: Retrofit
    ● Changes in SQLite database: Sqlbrite
    ● Changes in SharedPreferences: rx-preferences and prefser
    ● Location changes: Android-ReactiveLocation
    ● Network changes: ReactiveNetwork
    ● Stream of sensor readings: ReactiveSensors
    ● Stream of appearing BLE Beacons: ReactiveBeacons
    ● Reactive UI widgets: RxBinding
    ● and many more!
    programmer decides how to implement an Observable
    

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13. but...
    ...there is no silver bullet
    The Mythical Man-Month: Essays on Software Engineering - a book by Frederick Brooks
    interesting article available as *.pdf file at: http://worrydream.com/refs/Brooks-NoSilverBullet.pdf
    

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14. ...so when should we use RxJava?
    ● non-deterministic operations (we don’t know, when they will start or finish)
    ● long lasting operations
    ● processing large amount of data
    ● error prone operations
    

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15. RxJava is powerful library, but it’s just another tool
    ● Don’t use it everywhere and use it wisely
    ● Choose tools, which are the most appropriate for your solution
    ● Avoid over-engineering
    ● Keep your app simple
    

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16. Resources
    ● https://github.com/ReactiveX/RxJava/
    ● https://github.com/ReactiveX/RxJava/wiki
    ● http://reactivex.io/
    ● https://gist.github.com/staltz/868e7e9bc2a7b8c1f754 - Introduction to RxJava you’ve been missing
    ● https://speakerdeck.com/jakewharton/demystifying-rxjava-subscribers-oredev-2015
    ● https://speakerdeck.com/jakewharton/retrofit-and-rxjava-netflix-open-source-meetup-s02e02
    ● https://www.youtube.com/watch?v=sTSQlYX5DU0 - What does it mean to be reactive?
    ● http://blog.danlew.net/2014/09/15/grokking-rxjava-part-1/
    ● http://blog.danlew.net/2014/09/22/grokking-rxjava-part-2/
    ● http://blog.danlew.net/2014/09/30/grokking-rxjava-part-3/
    ● http://mttkay.github.io/blog/2013/08/25/functional-reactive-programming-on-android-with-rxjava/
    ● https://speakerdeck.com/benjchristensen
    ● http://rxmarbles.com/
    

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17. Reactive Live Coding
    Piotr Wittchen
    twitter.com/piotr_wittchen
    github.com/pwittchen
    piotr@wittchen.biz.pl
    wittchen.biz.pl
    

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