Get Reactive

Given at Droidcon UK 2015

The RxJava hype is still in full swing and almost everything gets Rxified. At least since the stable RxAndroid 1.0 release it’s time to take RxAndroid seriously!

In this session you will learn what RxJava is about, how to use it on Android and how RxAndroid can be used to build maintainable Android Apps from networking with Retrofit2 to UI with the new RxBinding and RxLifecycle libraries powered by MVP.

If you haven’t had the time to Get Reactive, we’ll provide a quick introduction why you should use RxAndroid in your current and next projects.

Transcript

1. Get Reactive
   

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2. +Wolfram Rittmeyer
   @rittmeyerw
   +Pascal Welsch
   @passsy
   

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3. Reactive Extensions
   

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4. RxJava – a library for composing
   asynchronous and event-based programs
   using observable sequences for the Java VM.
   https://github.com/ReactiveX/RxJava
   

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5. Reactive Extensions
   

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6. Simple Observable
   Observable countObservable =
   Observable.from(Arrays.asList(new Integer[]{2, 3, 5, 7}))
   .filter(n -> n % 2 != 0)
   .count()
   .map(n -> String.format("%d item(s)", n));
   

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7. Simple Subscriber
   countObservable.subscribe(new Subscriber() {
   @Override
   public void onCompleted() {
   Log.d("get_reactive", "Done!");
   }
   @Override
   public void onError(Throwable e) {
   Log.e("get_reactive", "Yikes!", e);
   }
   @Override
   public void onNext(String s) {
   Log.d("get_reactive", s);
   }
   });
   

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8. Simple Subscriber
   countObservable.subscribe(new Subscriber() {
   @Override
   public void onCompleted() {
   Log.d("get_reactive", "Done!");
   }
   @Override
   public void onError(Throwable e) {
   Log.e("get_reactive", "Yikes!", e);
   }
   @Override
   public void onNext(String s) {
   Log.d("get_reactive", s);
   }
   });
   

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9. RxJava in Detail
   

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10. Creating Observables
    ● Basic
    ○ Observable.from()
    ○ Observable.just()
    ○ Observable.range()
    ● Timing based
    ○ Observable.interval()
    ○ Observable.timer()
    ● Custom
    ○ Observable.create()
    

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11. Creating Observables
    Observable.create(new Observable.OnSubscribe() {
    public void call(Subscriber super Integer> s) {
    try {
    Random r = new Random();
    for (int i = 0; i < 10; i++) {
    s.onNext(r.nextInt());
    }
    s.onCompleted();
    }
    catch (Throwable t) {
    s.onError(t);
    }
    }
    });
    

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12. Creating Observables
    Observable.create(new Observable.OnSubscribe() {
    public void call(Subscriber super Integer> s) {
    try {
    Random r = new Random();
    for (int i = 0; i < 10; i++) {
    s.onNext(r.nextInt());
    }
    s.onCompleted();
    }
    catch (Throwable t) {
    s.onError(t);
    }
    }
    });
    

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13. Creating Observables
    Observable.create(new Observable.OnSubscribe() {
    public void call(Subscriber super Integer> s) {
    try {
    Random r = new Random();
    for (int i = 0; i < 10; i++) {
    if (!s.isUnsubscribed()) {
    s.onNext(r.nextInt());
    }
    else {
    break;
    }
    }
    // ...
    

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14. Consuming Observables
    ● subscribe() overloaded
    ● Be careful to not leak anything
    ○ anonymous inner classes
    ○ forgetting to unsubscribe
    

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15. Processing Chain
    ● Transformers
    ○ map, flatMap, scan
    ● Filters
    ○ filter, throttle, take, skip
    ● Conditions
    ○ amb, skipWhile, takeWhile
    ● Combination
    ○ concat, zip, combineLatest
    ● Aggregate
    ○ count, reduce, toList, toMap
    

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16. flatMap
    

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17. combineLatest
    

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18. zip
    

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19. Off the Main thread
    ● Schedulers
    ○ subscribeOn()
    ■ Schedulers.io()
    ■ Schedulers.computation()
    ■ Schedulers.newThread()
    ■ Schedulers.fromExecutor()
    ○ observeOn
    ■ AndroidSchedulers.mainThread()
    

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20. Error Handling
    ● Observable.onErrorResumeNext()
    ● Observable.onErrorReturn()
    ● yourObserver.onError()
    

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21. Backpressure
    ● Observable to fast for consumer
    ● Can happen anywhere in the chain
    ● Some possible actions:
    ○ Throttle
    ○ Buffer
    ○ request(n) upstream items
    

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22. Testing Observables
    ● Create special cases
    ○ Observable.error()
    ○ Observable.empty()
    ○ Observable.never()
    ● Use TestSubscriber
    

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23. Debugging Observables
    ● Side effect operators
    ○ doOnNext()
    ○ doOnSubscribe()
    ○ …
    ● Hooks
    ○ RxJavaObservableExecutionHook
    ○ RxJavaSchedulersHook
    ○ RxJavaErrorHandler
    

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24. RxAndroid
    

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25. RxAndroid
    // RxAndroid contains the AndroidScheduler (main thread)
    // few releases
    compile 'io.reactivex:rxandroid:1.0.1'
    // additionally add specific (latest) version of RxJava
    compile 'io.reactivex:rxjava:1.0.14'
    

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26. Reactive Android UI
    

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27. Make Listeners Reactive
    // typical Android widget listener
    final Button myButton = (Button) findViewById(R.id.myButton);
    myButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(final View v) {
    triggerAction();
    }
    });
    

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28. Make Listeners Reactive
    final Observable myButtonClickObservable =
    Observable.create(subscriber -> {
    myButton.setOnClickListener(v -> {
    if (!subscriber.isUnsubscribed()) {
    subscriber.onNext(v);
    }
    });
    });
    myButtonClickObservable
    .subscribe(v -> triggerAction());
    lamda for
    Observable.OnSubscribe
    unsubscribing not handled!
    

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29. Make Listeners Reactive
    final Observable myButtonClickObservable =
    Observable.create(subscriber -> {
    myButton.setOnClickListener(v -> {
    if (!subscriber.isUnsubscribed()) {
    subscriber.onNext(null);
    }
    });
    });
    myButtonClickObservable
    .delay(100, TimeUnit.MILLISECONDS)
    .observeOn(Schedulers.io())
    .subscribe(v -> triggerAction());
    

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30. compile 'com.jakewharton.rxbinding:rxbinding:0.3.0'
    RxView.clicks(myButton)
    .subscribe(v -> triggerAction());
    RxBinding
    Others and more
    RxView, RxTextView, RxAdapter, RxAdapterView, RxAutoCompleteTextView,
    RxCheckedTextView, RxCompoundButton, RxMenuItem, RxSeekBar, RxViewGroup,
    RxProgressBar, RxRadioGroup, RxRatingBar, RxRecyclerView, RxRecyclerViewAdapter,
    RxSearchView, RxToolbar, ...
    

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31. compile 'com.jakewharton.rxbinding:rxbinding:0.3.0'
    RxView.clicks(myButton)
    .subscribe(v -> triggerAction());
    RxBinding
    Others and more
    RxView, RxTextView, RxAdapter, RxAdapterView, RxAutoCompleteTextView,
    RxCheckedTextView, RxCompoundButton, RxMenuItem, RxSeekBar, RxViewGroup,
    RxProgressBar, RxRadioGroup, RxRatingBar, RxRecyclerView, RxRecyclerViewAdapter,
    RxSearchView, RxToolbar, ...
    rxbinding-support-v4
    rxbinding-appcompat-v7
    rxbinding-design
    rxbinding-recyclerview-v7
    rxbinding-leanback-v17
    

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32. Combine UI events
    

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33. The login view
    TextView username_tv = (TextView) findViewById(R.id.username);
    TextView password_tv = (TextView) findViewById(R.id.password);
    Observable rxUsername = RxTextView.textChanges(username_tv);
    Observable rxPassword = RxTextView.textChanges(password_tv);
    too easy...
    

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34. Build a registration view!
    TextView username_tv = (TextView) findViewById(R.id.username);
    TextView password_tv = (TextView) findViewById(R.id.password);
    TextView fullName_tv = (TextView) findViewById(R.id.fullName); // optional field
    Observable rxUsername = RxTextView.textChanges(username_tv);
    Observable rxPassword = RxTextView.textChanges(password_tv);
    Observable rxFullName = RxTextView.textChanges(fullName_tv);
    Observable.combineLatest(
    rxUsername, rxPassword, rxFullName, RegistrationModel::new)
    .filter(RegistrationModel::isValid)
    .subscribe(LoginActivity::enableSubmitButton);
    never called when fullName not entered
    

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35. combineLatest
    

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36. Build a registration view!
    TextView username_tv = (TextView) findViewById(R.id.username);
    TextView password_tv = (TextView) findViewById(R.id.password);
    TextView fullName_tv = (TextView) findViewById(R.id.fullName); // optional field
    Observable rxUsername = RxTextView.textChanges(username_tv);
    Observable rxPassword = RxTextView.textChanges(password_tv);
    Observable rxFullName = RxTextView.textChanges(fullName_tv)
    .mergeWith(Observable.just(""));
    Observable.combineLatest(
    rxUsername, rxPassword, rxFullName, RegistrationModel::new)
    // triggers now without entering a fullName
    .filter(RegistrationModel::isValid)
    .subscribe(LoginActivity::enableSubmitButton);
    emits "" after subscribe
    

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37. network requests
    triggered by UI
    

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38. GitHub repository
    search
    Using Retrofit 2 for the
    network calls
    

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39. the Android Way
    searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
    @Override
    public boolean onQueryTextChange(final String query) {
    if (!TextUtils.isEmpty(query)) {
    mGitApiService.searchRepositories(query).enqueue(callback);
    }
    return true;
    }
    @Override
    public boolean onQueryTextSubmit(final String query) {
    return false;
    }
    });
    

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40. the Android Way
    Callback callback
    = new Callback() {
    @Override public void onFailure(final Throwable t) {
    showEmptyErrorView(t.getMessage());
    }
    @Override
    public void onResponse(
    Response response, Retrofit retrofit) {
    if (response.isSuccess()) {
    showRepositories(response.body().getItems());
    } else {
    try {
    showEmptyErrorView(response.errorBody().string());
    } catch (IOException e) {
    showEmptyErrorView(response.message());
    // [\)\]\}]*
    

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41. the RxBeginner solution
    RxSearchView.queryTextChanges(searchView)
    .filter(charSequence -> !TextUtils.isEmpty(charSequence))
    .flatMap(charSequence -> {
    return mGitApiService
    .searchRepositoriesObservable(charSequence.toString())
    .subscribeOn(Schedulers.io());
    })
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(response -> {
    showRepositories(response.getItems());
    }, throwable -> {
    showEmptyErrorView(throwable.getMessage());
    });
    

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42. The RxBeginner solution
    RxSearchView.queryTextChanges(searchView)
    .filter(charSequence -> !TextUtils.isEmpty(charSequence))
    .flatMap(charSequence -> {
    return searchRepositories(charSequence);
    })
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(response -> {
    showRepositories(response.getItems());
    }, throwable -> {
    showEmptyErrorView(throwable.getMessage());
    });
    

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43. keep order with concatMap
    RxSearchView.queryTextChanges(searchView)
    .filter(charSequence -> !TextUtils.isEmpty(charSequence))
    .concatMap(charSequence -> {
    return searchRepositories(charSequence);
    })
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(response -> {
    showRepositories(response.getItems());
    }, throwable -> {
    showEmptyErrorView(throwable.getMessage());
    });
    

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44. handle backpressure
    RxSearchView.queryTextChanges(searchView)
    .filter(charSequence -> !TextUtils.isEmpty(charSequence))
    .throttleLast(100, TimeUnit.MILLISECONDS)
    .debounce(200, TimeUnit.MILLISECONDS)
    .onBackpressureLatest()
    .concatMap(charSequence -> {
    return searchRepositories(charSequence);
    })
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(response -> {
    showRepositories(response.getItems());
    }, throwable -> {
    showEmptyErrorView(throwable.getMessage());
    });
    prevents request for
    every character
    only one query waiting
    while request running
    

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45. handle error
    RxSearchView.queryTextChanges(searchView)
    .filter(charSequence -> !TextUtils.isEmpty(charSequence))
    .throttleLast(100, TimeUnit.MILLISECONDS)
    .debounce(200, TimeUnit.MILLISECONDS)
    .onBackpressureLatest()
    .concatMap(charSequence -> {
    return searchRepositories(charSequence);
    })
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(response -> {
    showRepositories(response.getItems());
    }, throwable -> {
    showEmptyErrorView(throwable.getMessage());
    });
    1. error not handled
    2. handled here
    3. completes Observable
    with error
    -> no more emits!
    

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46. handle error
    private Observable
    searchRepositories(CharSequence charSequence) {
    return mGitApiService
    .searchRepositoriesObservable(charSequence.toString())
    .subscribeOn(Schedulers.io())
    .onErrorResumeNext(throwable -> {
    // handle error somehow, change UI
    return Observable.empty();
    });
    } Observable
    completes without error
    and without result
    rx.Single doesn’t support
    this error handling :(
    

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47. Mock network requests
    // retrofit 2 interface
    @GET("/search/repositories")
    Observable>
    searchRepositoriesObservable(@Query("q") String name);
    // implementation
    @Override
    public Observable>
    searchRepositoriesObservable(final String name) {
    GitHubResponse response =
    new GitHubResponse<>(testRepo1, testRepo2, testRepoN);
    return Observable.just(response)
    .delay(1000, TimeUnit.MILLISECONDS);
    }
    

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48. cancel requests
    Call unsubscribe in #onStop();
    mSearchViewSubscription.unsubscribe();
    or use github.com/trello/RxLifecycle for it
    Use a Presenter (MVP) to continue the request during a
    configuration change
    Recommendation: Mosby or Nucleus
    github.com/sockeqwe/mosby github.com/konmik/nucleus
    

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49. +Wolfram Rittmeyer
    @rittmeyerw
    +Pascal Welsch
    @passsy
    

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