Reactive programming is a general programming term focused on reacting to changes, such as data values or events. It can and often is done imperatively. A callback, delegate is an approach to reactive programming done imperatively.

1. Reactive
Programming
Dwi Randy H - iOS Engineer

2. Overview
● What is Reactive Programming?
○ Reactive programming is a general programming term that is focused on reacting to changes, such
as data values or events. It can and often is done imperatively. A callback,delegate is an approach
to reactive programmingdone imperatively.
● Why we need Reactive Programming
○ More loosely coupled code
○ Make it easy to manage thread
○ A lot of operators that simplify work
○ Help to solve Real-Time Complex UI
○ Multi-platform standard

3. Example of Reactive Programming
A spreadsheet is a great example of reactive programming: cells dependent on other cells
automatically “react” when those other cells change.
Reference: https://learning.oreilly.com/library/view/reactive-programming-with/9781491931646/ch01.html

4. Rx Basic Building Blocks
● Observables = Dog
● Subscribers = Child
● Operators = Process
Down

5. Observables
Observable are the data source/stream, then that
observer reacts to whatever item or sequence of items
the observables emits.
They can emit data, completion and also failure

6. Hot and Cold Observables
Cold observables don’t do
anything until someone
starts observing them
(subscribe in Rx). They only
start running when they are
consumed
Hot Observables that can
active before subscription,
when an observer subscribes
to hot observable it will get
all values in the stream that
are emitted

7. Cold Observable

8. Hot Observable (Subject)

9. When We Need Cold or Hot
When we need to observable to
generating new values when
someone subscribing it and the
values are also not shared among
subscribers For example when we
call the API, Getting data from
local database
When you have Observable and we want
multiple subscribers to it, and you don’t
want them to cause regenerating the
values but rather reusing existing values
For example as LiveData in MVVM iOS
Reference: https://github.com/Reactive-Extensions/RxJS/blob/master/doc/gettingstarted/creating.md#cold-vs-hot-observables

10. Operator
An operator is simply a function that performs a
specific action. It takes a value, does something
with it and then returns it
● Creating
● Transforming
● Filtering
● Combining

11. Operator (Creating)
● Create
Create an observable from scratch by
calling observer method programmatically
● Just
Convert an object into Observable that
emits that object

12. Operator (Transforming)
● Map
Transform the items emitted by an
Observable by applying a function to each
item
● FlatMap
Transform the items emitted by an
Observable into Observables, then flatten
the emissions from those into a single
Observable

13. Observers
Observers consumes the data stream emitted by
observables
Observers subscribe to observable using subscribeOn()
method to receive data and then the data will be received
in onNext() callback()

14. Observer Callback
OnNext()
The callback to receive a
valueless notification of type
complete from the Observable.
OnComplete()
The callback to receive a
valueless notification of type
complete from the Observable.
onError()
The callback to receive notifications of
type error from the Observable, with an
attached Error.

15. Scheduler
Scheduler are component that tells observables
and observers on which thread they should run
- subscribeOn()
Specifies on which Scheduler to
Observables should operate
- observeOn()
Specifies on which Scheduler/Thread the
Subscribers should be notified

16. Scheduler Types Used
- Schedulers.io()
It is used for non CPU-intensive I/O type work
including interaction with the file system, performing
network calls, database interactions. This is usually
used in subscribeOn method
- Schedulers.computation
It is used for computational or CPU-intensive work
such as resizing images, processing large data sets,
Reference: https://proandroiddev.com/understanding-rxjava-subscribeon-and-observeon-
744b0c6a41ea
- AndroidSchedulers.trampoline
This is used to executes tasks in a FIFO (First
In, First Out). This scheduler runs the code on
current thread for example for Unit Testing
- AndroidSchedulers.mainThread()
This is used to bring back the execution to the
main thread so that UI modification can be
made. This is usually used in observeOn
method.

17. RxBinding & RxCocoa
- Library that makes it easier to use UI Component with reactive techniques.
Reference: https://github.com/ReactiveX/RxSwift

18. Thank you!