02-App-Architecture

Architecting your iOS App

Objectives

• Benefits/Goals of software architecture
• Design guidelines
• Practical tips

Benefits/Goals of software architecture

• Code is easy for other developers and yourself to comprehend
• Can adopt to changing requirements
• Can be reused and shared with other projects
• Manages complexity
• Over a long period of time, it saves you time because its easy to make changes

Design Guidelines

Think in Domains not in Objects

Better Architecture (Domain separation)

Single Responsibility Principle

• A class/object/struct/domain should only do one thing

Encapsulate

• Every component should know as little as possible about its surrounding components.
• Provide limited interfaces for components
• Reduces dependencies between components
• Makes it easier to replace components
• Eg. AnswerViewController only binds data from ViewModel, it knows nothing about the data, the ViewModel knows nothing about the view it is binding its data to, it only provides data.

Avoid the Massive View Controller

• Bad View Controller handles: Persistence, Business Logic, View Logic, etc.

Things a View Contoller should do

• Listen to callbacks from the View
• Invoke methods on the business/application layer
• Send responses from business/application layer back to the view

Things a View Controller should not do

• Construct complex network requests
• Construct complex database queries
• Take care of object serialization / deserialization

Practical Tips

Use View / View Model objects

View objects encapsulate multiple properties that are relevant for a type to be displayed by a custom view This is preferred over setting individual properties from outside the view

class AnswerCell: UICollectionViewCell {
    @IBOutlet var nameLabel: UILabel!
    @IBOutlet var profilePictureImageView: UIImageView!
    @IBOutlet var questionLabel: UITextField!

     var answerCellViewModel: AnswerCellViewModel? {
     didSet {
     nameLabel.text = answerCellViewModel?.name
     profilePictureImageView.image = answerCellViewModel?.profilePicture
     questionLabel.text = answerCellViewModel.question
 }

This allows you to prepare/format all the data nessasary to be displayed by the AnswerCell. Eg, format dates, format string(bold, italics etc) with NSAttributedString etc.

let answerCellViewModel = AnswerCellViewModel(
    name: "Eliel Gordon", 
    profilePicture: profilePicture, 
    question: "This is a question"
)

cell.answerCellViewModel = answerCellViewModel

Bad example

class AnswerCell: UICollectionViewCell {
    @IBOutlet var nameLabel: UILabel!
    @IBOutlet var profilePictureImageView: UIImageView!
    @IBOutlet var questionLabel: UITextField!
}

func cellForItem(at indexPath: IndexPath) -> UICollectionViewCell? {
    //....
    let answer = Answer()

    answerCell.nameLabel.text = "\(answer.sender.firstName)" + "\(answer.sender.lastName)"
    answerCell.questionLabel.text = answer.question.content
    //...

Whoever owns the answerCell now knows about the nameLabel and questionLabel of the answerCell

Encapsulate business logic

Summary

• Divide code into logical domains
• Strive for each unit of code having a single responsibility
• Define narrow and expressive APIs that hide
• Implementation details of other units of code and
• Reduce dependencies between your units
• Write code that is easy to delete, not to reuse

Resources

Refactor the Mega-Controller

Protocol Oriented Programming

Next Dependency - Management