Rx Java introduction

Talk from Xavier Lepretre

Transcript

1. RxJava Intro Functional reactive programming By Xavier Lepretre
2. What we want What we know
3. Imperative and synchronous var a = fetch(key); var b = transform(a); var c = transformAgain(b); return process(c);
4. Asynchronous with callbacks fetch(key, new Callback() { void onReceived(a) { transform(a, new Callback() { void onFinished(b) ... }); } });
5. Futures future = executor.submit(new Callback() { Object call() { return doLongExecution(); } }); a = future.get();
6. Nice to have, workflow description When done, do that fetch(key).then(a -> transform(a)) .then(b -> transformAgain(b)) .then(c -> process(c)) .then(d -> use(d));
7. Important classes
8. Observable<MyType> - like an object(s) pipe - no limit on number of objects piped - also pipes Throwable - signals when no more object, completed - can have many observers, like a multicast
9. Observer<MyType> - will receive: - the objects - the errors - the completed signal - can subscribe to many observables
10. Subscription - a handle to an observer subscribed to an observable - call .unsubscribe() when you no longer need to receive
11. Action1<MyType> { void call(MyType obj); } - 1 because it takes 1 parameter - There are Action2 … Action9
12. Func1<MyType, NextType> { public NextType call(MyType obj); } - 1 because it takes 1 parameter - There are Func2 … Func9
13. Important operations
14. .map(new Func1<A,B>(){}) - works on an object traveling along the pipe - transforms from one type to another - to be used when the transformation is synchronous - example: convert
16. .doOnNext(new Action1<A>(){}) - Works on a object from the pipe - Leaves the object unchanged - Example: save in cache, log
18. .flatMap(Func1<A, Observable<B>>) - Works on an object traveling along the pipe - Transforms from one type to another - To be used when the transformation is asynchronous - Example: network fetch, open dialog
20. Advantages - Unsubscription handles removing callback - Method can describe a subset of workflow
21. Create your own: OnSubscribe<> - Change callbacks into objects in pipeline - Know when to call onCompleted() - subscribeOn() - Subscriptions.create() - AndroidSubscriptions. unsubscribeInUiThread
22. Pitfalls - Forgot to .subscribe() - subscriptionList.unsubscribe(). Do not reuse - forgot observeOn(AndroidSchedulers. mainThread()) - callbacks may not show as used if you use retrolambda
23. Code Example https://github.com/xavierlepretre/rx-example
24. - All code shown is on client - Retrofit creates Observables -
25. - workflow pieces in methods: for dialog, no need to know next step - .onErrorResumeNext() to avoid break on less important elements - .flatMap() to show and wait for dialog - .publish() and .connect() to share Observable - SimpleAlertDialogOperator to convert a dialog into Observable