RxFy All The Things !

From Droidcon Paris 2014

Ever had to deal with terribly designed API or spent hours re-factoring your code to deal with an updated API?
You've heard about RxJava but can't see how it could benefit your project?
This talk will take the practical approach of a complex API to explain how RxJava and Functional Reactive Programming (FRP) can be used on every project to make your life easier.

Transcript

1. RxFy All The Things!
   No pain and easy refactoring
   

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2. @Dorvaryn
   +BenjaminAugustin-Dorvaryn
   Dorvaryn
   Benjamin Augustin
   Android Software Craftsman
   

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4. Why ?
   

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5. Development is hell
   

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6. So what is RxJava ?
   

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7. What is an Observable ?
   Single Multiple
   Sync T getData() Iterable getData()
   Async Future getData() Observable getData
   

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8. What is an Observable ?
   

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9. What is an Observer ?
   

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10. Resource
    RxJava wiki
    all the help you need
    https://github.com/ReactiveX/RxJava/wiki
    

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11. Schematics
    

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12. map
    ● Function
    ● Transformation
    ● For each element
    

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13. flatMap
    ● Function
    ● Composition
    ● For each element
    

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14. onErrorResumeNext
    ● Function
    ● Recovery
    ● On Failure
    

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15. Async control
    ● subscribeOn(Scheduler) :
    ○ Execute observable on Scheduler
    ● observeOn(Scheduler) :
    ○ Deliver results to observer on Scheduler
    

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17. All is starting well
    ● addToBasket
    ○ Take a barcode
    ○ Return a basket
    

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18. Easy enough right ?
    private class AddToBasket extends AsyncTask {
    private final API api;
    private final Basket currentBasket;
    private final BasketViewUpdater updater;
    AddToBasket(API api, Basket currentBasket, BasketViewUpdater updater) {
    this.api = api;
    this.currentBasket = currentBasket;
    this.updater = updater;
    }
    @Override
    protected Basket doInBackground(Barcode... barcodes) {
    return api.addToBasket(barcodes[0]);
    }
    @Override
    protected void onPostExecute(Basket response) {
    super.onPostExecute(response);
    updater.updateWith(response);
    }
    }
    

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19. After 4 months...
    private class AddToBasket extends AsyncTask>> {
    private final API api;
    private final Basket currentBasket;
    private final BasketViewUpdater updater;
    AddToBasket(API api, Basket currentBasket, BasketViewUpdater updater) {
    this.api = api;
    this.currentBasket = currentBasket;
    this.updater = updater;
    }
    @Override
    protected AsyncResult> doInBackground(Barcode... barcodes) {
    return AsyncResult.just(api.addToBasket(barcodes[0]));
    }
    @Override
    protected void onPostExecute(AsyncResult> response) {
    super.onPostExecute(response);
    new CheckForError(currentBasket, updater).execute(response);
    }
    }
    private class CheckForError extends AsyncTask>, Void, AsyncResult> {
    private final BasketViewUpdater updater;
    private final Basket currentBasket;
    CheckForError(Basket currentBasket, BasketViewUpdater updater) {
    this.currentBasket = currentBasket;
    this.updater = updater;
    }
    @Override
    protected AsyncResult doInBackground(AsyncResult>... responses) {
    AsyncResult> responseAsyncResult = responses[0];
    if(responseAsyncResult.isError()) {
    return AsyncResult.error(responseAsyncResult.error);
    }
    Response response = responseAsyncResult.value;
    if (response.isSuccess()){
    return AsyncResult.just(response.getValue());
    }
    return AsyncResult.error(new CustomError());
    }
    @Override
    protected void onPostExecute(AsyncResult basket) {
    super.onPostExecute(basket);
    new ApplyDiff(currentBasket, updater).execute(basket);
    }
    }
    private class ApplyDiff extends AsyncTask, Void, AsyncResult> {
    private final Basket currentBasket;
    private final BasketViewUpdater updater;
    

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20. So how to RxFy it ?
    

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21. Rx Style
    class BasketObserver implements Observer {
    public onNext(Basket basket) {
    updateUI(basket);
    }
    public onError(Throwable error) {
    displayDialogFor(error);
    }
    public onComplete() {
    }
    }
    

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22. Rx Style
    Definition:
    Usage:
    public Observable addToBasket(Barcode code);
    addToBasket(code)
    .subscribe(new BasketObserver());
    

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23. HTTP Standard ?
    

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24. Refactoring
    public Observable addToBasket(Barcode code) {
    return addToBasketReq(code).flatmap(checkAPISuccess());
    }
    private Observable> addToBasketReq(Barcode code);
    Definition:
    addToBasket(code)
    .subscribe(new BasketObserver());
    Usage:
    

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25. flatMap
    ● Function
    ● Composition
    ● For each element
    

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26. Function
    public Func1, Observable> checkApiSuccess() {
    return new Func1, Observable>() {
    @Override
    public Observable call(Response response) {
    if (response.isSuccess()) {
    return Observable.from(response.getBody());
    }
    return Observable.error(new CustomError(header));
    }
    };
    }
    

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27. Stateless ?
    

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28. Refactoring
    public Observable addToBasket(Barcode code) {
    return addToBasketReq(code)
    .flatmap(checkAPISuccess())
    .map(applyDiffTo(cachedBasket));
    }
    Definition:
    

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29. map
    ● Function
    ● Transformation
    ● For each element
    

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30. Function
    public Func1 applyDiffTo(final Basket basket) {
    return new Func1() {
    @Override
    public Basket call(Diff diff) {
    return basket.apply(diff);
    }
    };
    }
    

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31. Logic server side ?
    

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32. Refactoring
    public Observable addToBasket(Barcode code) {
    return addToBasketReq(code)
    .flatmap(checkAPISuccess())
    .flatmap(addCustomerIfNeeded())
    .map(applyDiffTo(cachedBasket));
    }
    Definition:
    

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33. Function
    private Func1> addCustomerIfNeeded() {
    return new Func1>() {
    @Override
    public Observable call(Diff diff) {
    if (diff.requireAddCustomer()) {
    return addCustomer(diff.getCustomerId());
    }
    return Observable.from(diff);
    }
    };
    }
    

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34. Oh what about the law ?
    

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35. UI in network flow ?
    

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36. Refactoring
    public Observable addToBasket(Barcode code) {
    return addToBasket(code, Data.emptyData);
    }
    public Observable addToBasket(Barcode code, Data data) {
    return addToBasketReq(code, data)
    .flatmap(checkAPISuccess())
    .flatmap(addCustomerIfNeeded())
    .map(applyDiffTo(cachedBasket))
    .onErrorResumeNext(checkForError(continuation(code)));
    }
    Definition:
    

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37. onErrorResumeNext
    ● Function
    ● Recovery
    ● On Failure
    

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38. Function
    public Func1> checkForError(final Func1Observable> continuation) {
    return new Func1>() {
    @Override
    public Observable call(Throwable error) {
    if (error instanceof BusinessRuleExeption) {
    return Observable.error(new NeedMoreDataException(continuation));
    }
    return Observable.error(error);
    }
    };
    }
    

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39. Function
    public Func1> continuation(final Barcode
    barcode) {
    return new Func1> {
    @Override
    public Observable call (Data data){
    return addToBasket(barcode, data);
    }
    }
    }
    

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40. Observer
    class BasketObserver implements Observer {
    public onNext(Basket basket) {
    updateUI(basket);
    }
    public onError(Throwable error) {
    displayDialogFor(error).flatmap(withContinuationFrom(error));
    }
    public onComplete() {
    }
    }
    

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41. Function
    private Observable displayDialogFor(Throwable error);
    private Func1> withContinuationFrom(NeedMoreData
    error) {
    return new Func1>() {
    @Override
    public Observable call(final Data data) {
    return error.getContinuation().call(data);
    }
    };
    }
    

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42. Dialog is reactive
    public class ReactiveDialog extends DialogFragment {
    public Observable show(final FragmentManager manager) {
    return Observable.create(new Observable.OnSubscribe() {
    @Override
    public void call(rx.Subscriber super T> subscriber) {
    UUID key = subscriberVault.store(subscriber);
    getArguments().putSerializable(REACTIVE_DIALOG_KEY, key);
    show(manager, getClass().getSimpleName());
    }
    });
    }
    }
    

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43. Reactive Dialogs ?!
    

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44. Recap
    public Observable addToBasket(Barcode code, Data data) {
    return addToBasketReq(code, data)
    .flatmap(checkAPISuccess())
    .flatmap(addCustomerIfNeeded())
    .map(applyDiffTo(cachedBasket))
    .onErrorResumeNext(checkForError(continuation(code, data)));
    }
    Definition:
    

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46. Resource
    RxAndroid
    collection of tools for RxJava on Android
    https://github.com/ReactiveX/RxAndroid
    

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47. Resource
    RxJava workshop
    a simple workshop to start
    http://goo.gl/eI3hMc
    

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48. We’re hiring !
    join@novoda.com
    

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49. Questions ?
    

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50. @Dorvaryn
    +BenjaminAugustin-Dorvaryn
    Dorvaryn
    Benjamin Augustin
    Android Software Craftsman
    

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