Mobile Architecture Patterns

Question 1

Advantages of a Clean Architecture

Answer 1

Testable
Independent of frameworks
Independent of the UI (UI changes don’t affect others)
Independent of data sources (data sources changes don’t change other layers)
Independent of external elements (business logic is independent of all things around it)

Question 2

Overview of Apple MVC

Answer 2

View
Sends user action to Controller

Controller
Notifies Model of data updates
Renders updates to the view

Model
Updates data
Sends updates to Controller

Deviates from original MVC in that model updates flow though the Controller (rather than to the view directly)

Question 3

Describe M (Model) in MVC

Answer 3

Holds the business logic
Access, manipulates, and stores the data

Contains network classes (if needed)

Parses incoming data and converts into model objects

Must not communicate directly with the view (goes through the Controller)

Question 4

Describe V (View) in MVC

Answer 4

Components that the user can see

These components receive user interactions

Question 5

Describe C (Controller) in MVC

Answer 5

Main component

Communicates between View and Model

If model data changes, updates the view with changes

Takes care of the application lifecycle

Question 6

Advantages of MVC architecture

Answer 6

Simple design
Uses less code
Clear separation of responsibilities
Quick development

Question 7

When to use MVC pattern

Answer 7

simple screens that don’t require complex state & data manipulation

Question 8

What does MVVM stand for ?

Answer 8

Model - View - ViewModel

4 part design - also a separate VC

Question 9

Describe V in MVVM

Answer 9

View
- Presents information and responds to user interaction.
- UIKit only accessible from View
- Binds to model using data binding

Question 10

Describe VM in MVVM

Answer 10

ViewModel - Handles state and prepares data for presentation by the view (ex: formatting date/time strings). Uses delegates to interact with the View

Communicates with Model using observable / data-binding (which requires something like Bond lib or RXSwift (heavy))

Question 11

Describe M in MVVM

Answer 11

Model - Business logic and responsible for accessing persistent store and networking requests

Communicates with ViewModel using data-binding

Question 12

Why use MVVM

Answer 12

• More modern design pattern
• Allows better separation of concerns
• Handles complex state management and data manipulation

Question 13

How would you implement navigation in an MVVM arch ?

Answer 13

Options

1 - ViewModel - trigger the nav and choose where to go. View handles the actual navigation

2 - ViewModel - triggers the navigation. View determines where to go and handles the navigation

3- ViewModel - triggers the navigation. NavCoordinator determines where to go. NavCoordinatior tells view where to go ????

Question 14

Why is MVVM good for testability ?

Answer 14

State and data manipulation are both in ViewModel. ViewModel can be easily setup and tested without the UI

Question 15

Ways to handle Dependency Injection

Answer 15

Constructor injection

Setter injection - Property on object sets the value

Method injection - Each function takes a param

Question 16

How is the delegate pattern different from notifications or Combine (SwiftUI ?)

Answer 16

Delegates are 1-to-1

Formalized protocol

Can be complex to setup

Question 17

Disadvantages to singleton pattern ?

Answer 17

• Requires global state (hard to track who changes it)
• Increases coupling
• Challenges due to multi-threading

Question 18

Ways to make singleton thread safe ?

Answer 18

1- Use GCD to require access on main thread

DispatchQueue.global.async() { DispatchQueue.main.async {
MySingleton.shared.doSomething()
} }

2- Make thread-safe using NSLock

Question 19

Describe the MVP pattern

Answer 19

Model - View - Presenter

An extension of the Apple MVC pattern where View / VC are merged and Presenter is the intermediary

Question 20

Describe M in MVP pattern

Answer 20

Model

• Handles application data and persistence

Question 21

Describe View in MVP pattern

Answer 21

View (and View Controller)

Takes care of UI setup and forwards events to Presenter

Question 22

Describe P in MVP pattern

Answer 22

Presenter

The business logic of the application. It formats data for the UI and updates it (through View) using delegate methods.

No UIKit code, so it is easily testable

Question 23

Advantages of MVVM pattern

Answer 23

Testability (using mock views)

Question 24

Disadvantages of MVVM pattern

Answer 24

Increased complexity due to the need to data binding (which is not a core part of iOS frameworks).