Reactive VIPER

IVAN ĐIKIĆ

WHY?

UIVIEWCONTROLLER (UIVIEW)

• workhorse

• hard to test

• hard to maintain

• not reusable

BUILDING BLOCK FOR COCOA TOUCH

VIPER

• in 4 parts

• good for medium to big size applications

• good separation of responsibility

• loosely coupled components

SPLIT UP VIEW CONTROLLER

• connection between components is achieved using protocols

• composition instead inheritance in most cases

• most of UI is done in Storyboards but without Segues

GENERAL

• View / View Controller

• Presenter (view model :))

• Interactor

• Wireframe

MAIN COMPONENTS

MAIN COMPONENTS

MAIN COMPONENTS

• business logic agnostic

• knows how to layout itself

• reusable

VIEW / VIEW CONTROLLER

• business logic

• least reusable part

• has reference to

• view

• interactor

• wireframe

• models data received from interactor

• views delegate (responds to view events)

PRESENTER

• has the data

• knows how to get the data

INTERACTOR

• knows how to navigate

• knows how to create other VIPER modules

WIREFRAME

RX(SWIFT)

• FRP

• functional programming

• functions don’t have side effects, no mutable state

• difficult to program since real world is all about side effects

• reactive programming

• changes propagate throughout a system automatically

• functional reactive programming

• we model user input as a function that changes over time,

abstracting away the idea of mutable state

CREATED BY MICROSOFT (RX.NET)

• sweet spot between functional and imperative programming world

• unifies various design patterns (GoF)

• Delegate

• Callback (Closures, Blocks)

• KVO

• Notifications

• Observer

• enables building apps in declarative style

WHY RX?

DECLARATIVE STYLE

Observable .combineLatest

( firstName.rx_text, lastName.rx_text

) {

$0 + " " + $1 }

.map { "Greetings, \($0)"

} .bindTo(greetingLabel.rx_text)

ITERATOR, OBSERVER

Observer and Iterator patterns are mathematical duals

CORE KNOWLEDGE

ITERATOR PATTERN

• pull based interface

• good for traversing collections

• standard interface

• generator

• next (pull)

• no more data

• throw (error)

• arrays, dictionaries, sets

ITERATOR

• a collection of protocols

• CollectionType

• SequenceType

• GeneratorType

ITERATOR IN SWIFT

GeneratorType - serve elements

protocol GeneratorType { associatedtype Element mutating func next() -> Element? }

SequenceType - knows how to create generator struct PrefixSequence: SequenceType { let string: String func generate() -> PrefixGenerator { return PrefixGenerator(string: string) } }

CollectionType

- repeatable iteration - access to the elements via index

struct BeersCollection<T> { let beers: [T] }

CollectionType extension BeersCollection: SequenceType {

typealias Generator = AnyGenerator<T>

func generate() -> AnyGenerator<T> { var i = 0

return AnyGenerator { i += 1 return i >= self.beers.count ? nil : self.beers[i] } } }

OBSERVER PATTERN

• push based interface

• good for UI events

• missing

• error handling

• no more data

OBSERVER

Observer

protocol PropertyObserver : class { func willChangePropertyName(propertyName: String, newPropertyValue: AnyObject?) func didChangePropertyName(propertyName: String, oldPropertyValue: AnyObject?) }

Observer

class TestChambers {

weak var observer: PropertyObserver?

var testChamberNumber: Int = 0 { willSet(newValue) { observer?.willChangePropertyName("testChamberNumber", newPropertyValue:newValue) } didSet { observer?.didChangePropertyName("testChamberNumber", oldPropertyValue:oldValue) } } }

OBSERVABLES AKA

SEQUENCES

• unifying Iterator and Observer pattern

• can be composed

• we already know how to do operations on collections

• map

• filter

• reduce

• the equivalence of observer pattern (Observable<Element>

sequence) and normal sequences (SequenceType) is the most

important thing to understand about Rx

GENERAL

• every observable sequence is just a sequence

• push interface (aka callback)

• regex

• next* (error | completed)?

• can have 0 or more elements

• once error or completed

• sequence cannot produce any other element

• all internal resources will be disposed

• no work will be performed until you call subscribe

OBSERVABLES AKA SEQUENCES

TIPS’N’TRICKS

RTFM

AVOID NESTING CALLS

ALWAYS USE `DISPOSE BAG`

`SOURCEKIT` HAS CRASHED

USE [WEAK SELF]

PERIODICALLY PRINT RESOURCES COUNT

STRIVE TO MODEL YOUR SYSTEMS AS PURE FUNCTIONS

RESOURCES

RESOURCES

• RxSwift • Reactive Programming Overview • Design Patterns In Swift • Inside .Net Reactive Framework • Duality • Visual Operators (RxMarbles)

Q&A