Rx Study Guide.md

Rx Study Guide

Visual guide - RxMarbles

Observable

What is an Observable How to create an Observable:

• just
• of
• from
• create
• deferred
• timer

What is the difference between cold and hot Observables How does an Observable stream end

Observer/Subscriptions/Disposables

What is an Observer What is a subscription:

• How to subscribe to an Observable?
• If you subscribe to an Observable, does it always send the whole stream? (test this specially with create and deferred)
• What is a Disposable?
• What happens if a Disposable is disposed before the stream ends?
• If nobody holds a Disposable instance, what happens?

Observable operations

What these operations do:

COMBINATION	FILTERING	MATHEMATICAL	TRANSFORMATION	UTILITY
combineLatest	distinctUntilChanged	count	buffer	delay
concat	elementAt	reduce	concatMap	delaySubscription
merge	filter		concatMapTo	retry/retryWhen
startWith	debounce		map
withLatestFrom	ignoreElements		mapTo
zip	last		scan
	sample
	skip
	skipUntil
	skipWhile
	take
	takeLast
	takeUntil
	takeWhile
	throttle

Special Kinds of Observables/Streams

PublishSubject, BehaviorSubject, Variable/BehaviorRelay: What are the differences between each other and normal Observables/Observers

Variable is in the process of being deprecated for BehaviorRelay, essentially they do the same thing

Traits - Specific kinds of Observables

What are, and what do they "guarantee":

• Single
• Maybe
• Completable
• ControlProperty
• ControlEvent
• Driver

What happens when you create a Single/Maybe and emit an next event twice?

What kind of errors do traits usually throw, and when?

How do you chain Observable sequences? What about Completables?

How do you apply/switch to different traits?

• Observable -> Single | Maybe | Completable
• Single -> Single | Maybe | Completable
• Maybe -> Single | Maybe | Completable
• Completable -> Single | Maybe | Completable

Some of the conversions above do not make sense, why?

What/where a Driver is mostly used for/on?

Schedulers

What kind of schedulers are there (First must understand Threads - Concurrent and Serial) What is subscribeOn and observeOn How is a computation scheduled to a specific thread?

Testing

If your test target exposes an Observable, what should be asserted of it?

Observables are essentially encapsulated asyncronous operations:

• Do you need to assert the time the operation took?
• Do you need to assert only the results? Then how do you block execution while waiting for the stream to end?
• Do you need to assert which events are sent while modifying the source? Then how do you check the values received?

How would you create a testing hot/cold sequence? Look for TestScheduler after trying to answer, and check which would work better for your test.