MVVM & RxSwift

MVVM ! RxSwift

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HELLO!!!

Dang Thai Son

• iOS Developer 2+ years experience

• Interested in Functional Programming

• Going to learn Elm/Haskell this year.

• Blog: https://dangthaison91.wordpress.com


Who is you writing Swift?


Did you ever know MVVM or using it now?


Functional Reactive

Programming?


Why MVVM?


MVC is the Kinghttps://dangthaison91.wordpress.com | fb.me/dangthaison.91 | @dangthaison91 7

You drunk!!!


Apple’s Expected MVC


Actual Apple’s MVC


MVC

Start project from scratch:

• Project grow bigger with more features

• Run for deadline=> Do you try to update / add functions after 1-2 months later?


Actual Apple’s MVC


MVC

Plain old MVC is leads to huge, disorganized, unmaintainable code (most of it in a UIViewController).


MVVM


View Controllers

• Responsible for controlling views (Layout, Animation, Colors, Presenting VC...)

• Tell ViewModel when something happens (handles user interaction).

• Listen to ViewModel (network request completes, data changed).


View Models

• Perform all the business logic (fire-off network requests, fetch Core Data objects, validate input...)

• Deliver necessary data to view controllers to display: Date/String format.

• Update and listen to changes in models


Demo


Advantages

1. Maintainability

• Separation of concerns

• Redesign UI

2. Testability

• Easy to write unit test.

• No require UI Automation

3. Extensibility: More reusable for iOS, watchOS, MacOS...


Disadvantages

• Can be overkill for Simple UI: Tutorial/Walkthrough

• Massive View Controller will become Massive ViewModel

• MVC is has better speed of the development.

• Hard to design the ViewModel.


Rules!!!


View Controllers

• View only knows the view controllers, notifying them of interaction events (same as MVC).

• View controller can't talk to models directly, they only interact with view models and views.


View Models

• Don’t import UIKit.

• View Model only knows models.

• View Model doesn't know Views/View Controllers


MVVM is silver bullet and will save your life from MVC?


Just a SMALL improvement!


How can ViewModel notify

data changes?


Delegate?


KVONSNotification


Maybe[Closure]


Microsoft created MVVM.

What do they thing?


Rx Extension for Binding


What is Functinal Reactive Programming?

• FRP is about datatypes that represent a value ‘over time’

• FRP is programming with asynchronous data streams.

• ...


FRP is programming with streams of values over time


Now for magic!


What we can do

• Observables

• Transformations

• Composition

• Combination

• Filter

• Buffer...


FRP is just Binding???


FRP Advantages

• Code more concise & clear, easy to understand without context

• Readability, highly express

• Make Asynchronous easier

• UI Binding

• Maintainability, Extensibility...


What are the advantages we got

in production?


FRP Advantages

• Readable declarative code: review, test, debug

• Has a standard mechanism for error recovery.

• Composing is awesome!!!


FRP Advantages

• Handling UI interactions/events/state is insanely easy

• Reduce side-effects & using mutable values.

• Remove “callback hell”


FRP Advantages

FRP helps us focus on solving the problem rather than the required procedure.


Visit my blog!


Best Practices!


Best Practices

View Model doesn't know about View Controller.

=> So how it give know what information VC need?


Protocol


Best Practices



Best Practices

Immutable View Model: Dependence injection via initializer


Best Practices

Storyboard???


Explicit Data Flow


Flux


Demo: Github Search


MVVM rules with RxSwift

View cannot modify the data.View only knows how to present the data.

• BadviewModel.title

.map { $0 + "!!!" } // View should not modify the data

.bindTo(self.titleLabel)

• Good

viewModel.title

.bindTo(self.titleLabel)



View doesn't know what ViewModel does.View can only communicate to ViewModel about what View did.

• BadviewModel.login() // Bad: View should not know what ViewModel does (login)

• Good

self.loginButton.rx_tap

.bindTo(viewModel.loginButtonDidTap) // "Hey I clicked the login button"



Model is hidden by ViewModel. ViewModel only exposes the minimum data so that View can render.

• Bad

struct ProductViewModel {

let product: Driver<Product> // Bad: ViewModel should hide Model

}

• Good

struct ProductViewModel { let productName: Driver<String> let formattedPrice: Driver<String>}


Tips

• Handle error: parse Error Message in ViewModel then expose as String.

=> Oops, we are doing it wrong too.

• Don't make ViewModelM become Presenter layer: number of rows, color...


Naming?


There are only two hard things in Computer Science:Cache invalidation and Naming things.

— Phil Karlton


Naming?

• Relate to Data, Action, not related to UI

• Input: Trigger, Source, Action...

• Output: Signal, Sink...


Q&Ahttps://dangthaison91.wordpress.com | fb.me/dangthaison.91 | @dangthaison91 59

Q&A

View Model should be Struct or Class?


Q&A

N-ViewController <-> 1-ViewModel?


Q&A

1-ViewController <-> N-ViewModel !!!


Q&AWhere MVVM suck: UI with complex state & levels.

=> Solution:

• VIPER !

• Flux/Redux ""


Reactive with us, we are hiring!

• PHP/Ruby Backend

• Android Developer

• iOS with Swift

• Designer

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MVVM & RxSwift

Software