RxJava Intro Functional reactive programming By Xavier Lepretre 

What we want What we know 

Imperative and synchronous var a = fetch(key); var b = transform(a); var c = transformAgain(b); return process(c); 

Asynchronous with callbacks fetch(key, new Callback() { void onReceived(a) { transform(a, new Callback() { void onFinished(b) ... }); } }); 

Futures future = executor.submit(new Callback() { Object call() { return doLongExecution(); } }); a = future.get(); 

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)); 

Important classes 

Observable - 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 

Observer - will receive: - the objects - the errors - the completed signal - can subscribe to many observables 

Subscription - a handle to an observer subscribed to an observable - call .unsubscribe() when you no longer need to receive 

Action1 { void call(MyType obj); } - 1 because it takes 1 parameter - There are Action2 … Action9 

Func1 { public NextType call(MyType obj); } - 1 because it takes 1 parameter - There are Func2 … Func9 

Important operations 

.map(new Func1(){}) - works on an object traveling along the pipe - transforms from one type to another - to be used when the transformation is synchronous - example: convert 

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.doOnNext(new Action1(){}) - Works on a object from the pipe - Leaves the object unchanged - Example: save in cache, log 

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.flatMap(Func1>) - 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 

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Advantages - Unsubscription handles removing callback - Method can describe a subset of workflow 

Create your own: OnSubscribe<> - Change callbacks into objects in pipeline - Know when to call onCompleted() - subscribeOn() - Subscriptions.create() - AndroidSubscriptions. unsubscribeInUiThread 

Pitfalls - Forgot to .subscribe() - subscriptionList.unsubscribe(). Do not reuse - forgot observeOn(AndroidSchedulers. mainThread()) - callbacks may not show as used if you use retrolambda 

Code Example https://github.com/xavierlepretre/rx-example 

- All code shown is on client - Retrofit creates Observables - 

- 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