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 King

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?

KVO
NSNotification

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.
• Bad
viewModel.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.
• Bad
viewModel.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&A

Q&A
View Model should be Struct or Class?

Q&A
N-ViewController <-> 1-ViewModel?

Q&A
1-ViewController <-> N-ViewModel !!!

Q&A
Where 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
https://itviec.com/companies/innovatube

Thank you!
https://dangthaison91.wordpress.com
@dangthaison91

MVVM & RxSwift

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