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
2. @Dorvaryn +BenjaminAugustin-Dorvaryn Dorvaryn Benjamin Augustin Android Software Craftsman
4. Why ?
5. Development is hell
6. So what is RxJava ?
7. What is an Observable ? Single Multiple Sync T getData() Iterable<T> getData() Async Future<T> getData() Observable<T> getData
8. What is an Observable ?
9. What is an Observer ?
10. Resource RxJava wiki all the help you need https://github.com/ReactiveX/RxJava/wiki
11. Schematics
12. map • Function • Transformation • For each element
13. flatMap • Function • Composition • For each element
14. onErrorResumeNext • Function • Recovery • On Failure
15. Async control • subscribeOn(Scheduler) : ◦ Execute observable on Scheduler • observeOn(Scheduler) : ◦ Deliver results to observer on Scheduler
17. All is starting well • addToBasket ◦ Take a barcode ◦ Return a basket
18. Easy enough right ? private class AddToBasket extends AsyncTask<Barcode, Void, Basket> { 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); } }
19. After 4 months... private class AddToBasket extends AsyncTask<Barcode, Void, AsyncResult<Response<Diff>>> { 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<Response<Diff>> doInBackground(Barcode... barcodes) { return AsyncResult.just(api.addToBasket(barcodes[0])); } @Override protected void onPostExecute(AsyncResult<Response<Diff>> response) { super.onPostExecute(response); new CheckForError(currentBasket, updater).execute(response); } } private class CheckForError extends AsyncTask<AsyncResult<Response<Diff>>, Void, AsyncResult<Diff>> { private final BasketViewUpdater updater; private final Basket currentBasket; CheckForError(Basket currentBasket, BasketViewUpdater updater) { this.currentBasket = currentBasket; this.updater = updater; } @Override protected AsyncResult<Diff> doInBackground(AsyncResult<Response<Diff>>... responses) { AsyncResult<Response<Diff>> responseAsyncResult = responses[0]; if(responseAsyncResult.isError()) { return AsyncResult.error(responseAsyncResult.error); } Response<Diff> response = responseAsyncResult.value; if (response.isSuccess()){ return AsyncResult.just(response.getValue()); } return AsyncResult.error(new CustomError()); } @Override protected void onPostExecute(AsyncResult<Diff> basket) { super.onPostExecute(basket); new ApplyDiff(currentBasket, updater).execute(basket); } } private class ApplyDiff extends AsyncTask<AsyncResult<Diff>, Void, AsyncResult<Basket>> { private final Basket currentBasket; private final BasketViewUpdater updater;
20. So how to RxFy it ?
21. Rx Style class BasketObserver implements Observer<Basket> { public onNext(Basket basket) { updateUI(basket); } public onError(Throwable error) { displayDialogFor(error); } public onComplete() { } }
22. Rx Style Definition: Usage: public Observable<Basket> addToBasket(Barcode code); addToBasket(code) .subscribe(new BasketObserver());
23. HTTP Standard ?
24. Refactoring public Observable<Basket> addToBasket(Barcode code) { return addToBasketReq(code).flatmap(checkAPISuccess()); } private Observable<Response<Basket>> addToBasketReq(Barcode code); Definition: addToBasket(code) .subscribe(new BasketObserver()); Usage:
25. flatMap • Function • Composition • For each element
26. Function public Func1<Response<Basket>, Observable<Basket>> checkApiSuccess() { return new Func1<Response<Basket>, Observable<Basket>>() { @Override public Observable<Basket> call(Response<Basket> response) { if (response.isSuccess()) { return Observable.from(response.getBody()); } return Observable.error(new CustomError(header)); } }; }
27. Stateless ?
28. Refactoring public Observable<Basket> addToBasket(Barcode code) { return addToBasketReq(code) .flatmap(checkAPISuccess()) .map(applyDiffTo(cachedBasket)); } Definition:
29. map • Function • Transformation • For each element
30. Function public Func1<Diff, Basket> applyDiffTo(final Basket basket) { return new Func1<Diff, Basket>() { @Override public Basket call(Diff diff) { return basket.apply(diff); } }; }
31. Logic server side ?
32. Refactoring public Observable<Basket> addToBasket(Barcode code) { return addToBasketReq(code) .flatmap(checkAPISuccess()) .flatmap(addCustomerIfNeeded()) .map(applyDiffTo(cachedBasket)); } Definition:
33. Function private Func1<Diff, Observable<Diff>> addCustomerIfNeeded() { return new Func1<Diff, Observable<Diff>>() { @Override public Observable<Diff> call(Diff diff) { if (diff.requireAddCustomer()) { return addCustomer(diff.getCustomerId()); } return Observable.from(diff); } }; }
34. Oh what about the law ?
35. UI in network flow ?
36. Refactoring public Observable<Basket> addToBasket(Barcode code) { return addToBasket(code, Data.emptyData); } public Observable<Basket> addToBasket(Barcode code, Data data) { return addToBasketReq(code, data) .flatmap(checkAPISuccess()) .flatmap(addCustomerIfNeeded()) .map(applyDiffTo(cachedBasket)) .onErrorResumeNext(checkForError(continuation(code))); } Definition:
37. onErrorResumeNext • Function • Recovery • On Failure
38. Function public Func1<Throwable, Observable<Basket>> checkForError(final Func1<Data, Observable<Basket>> continuation) { return new Func1<Throwable, Observable<Basket>>() { @Override public Observable<Basket> call(Throwable error) { if (error instanceof BusinessRuleExeption) { return Observable.error(new NeedMoreDataException(continuation)); } return Observable.error(error); } }; }
39. Function public Func1<Data, Observable<Basket>> continuation(final Barcode barcode) { return new Func1<Data, Observable<Basket>> { @Override public Observable<Basket> call (Data data){ return addToBasket(barcode, data); } } }
40. Observer class BasketObserver implements Observer<Basket> { public onNext(Basket basket) { updateUI(basket); } public onError(Throwable error) { displayDialogFor(error).flatmap(withContinuationFrom(error)); } public onComplete() { } }
41. Function private Observable<Data> displayDialogFor(Throwable error); private Func1<Data, Observable<Basket>> withContinuationFrom(NeedMoreData error) { return new Func1<Data, Observable<T>>() { @Override public Observable<Basket> call(final Data data) { return error.getContinuation().call(data); } }; }
42. Dialog is reactive public class ReactiveDialog<T> extends DialogFragment { public Observable<T> show(final FragmentManager manager) { return Observable.create(new Observable.OnSubscribe<T>() { @Override public void call(rx.Subscriber<? super T> subscriber) { UUID key = subscriberVault.store(subscriber); getArguments().putSerializable(REACTIVE_DIALOG_KEY, key); show(manager, getClass().getSimpleName()); } }); } }
43. Reactive Dialogs ?!
44. Recap public Observable<Basket> addToBasket(Barcode code, Data data) { return addToBasketReq(code, data) .flatmap(checkAPISuccess()) .flatmap(addCustomerIfNeeded()) .map(applyDiffTo(cachedBasket)) .onErrorResumeNext(checkForError(continuation(code, data))); } Definition:
46. Resource RxAndroid collection of tools for RxJava on Android https://github.com/ReactiveX/RxAndroid
47. Resource RxJava workshop a simple workshop to start http://goo.gl/eI3hMc
48. We’re hiring ! join@novoda.com
49. Questions ?
50. @Dorvaryn +BenjaminAugustin-Dorvaryn Dorvaryn Benjamin Augustin Android Software Craftsman