Protocol-Oriented MVVM (extended edition)

"Swift Is a Protocol-Oriented
Programming Language"
— Dave Abrahams, Professor of Blowing-Your-Mind

UITableViewDelegate
UITableViewDataSource
UITextFieldDelegate
NSURLSessionDelegate
CLLocationManagerDelegate
MCSessionDelegate

Artsy Engineering: MVVM in Swift

VIEW
Your balance is $6,729,383.99

VIEWMODEL
struct AccountViewModel {
let displayBalance: String
init(model: BankAccount) {
let formattedBalance = model.balance.currencyValue
displayBalance = "Your balance is (formattedBalance)"
}
}

VIEWCONTROLLER
var viewModel = ViewModel(model: Account)

THE PROBLEM
class SwitchWithTextTableViewCell: UITableViewCell {
func configure(
title: String,
titleFont: UIFont,
titleColor: UIColor,
switchOn: Bool,
switchColor: UIColor = .purpleColor(),
onSwitchToggleHandler: onSwitchToggleHandlerType? = nil)
{
// configure views here
}
}

protocol SwitchWithTextCellProtocol {
var title: String { get }
var titleFont: UIFont { get }
var titleColor: UIColor { get }
var switchOn: Bool { get }
var switchColor: UIColor { get }
func onSwitchTogleOn(on: Bool)
}

extension SwitchWithTextCellProtocol {
var switchColor: UIColor {
return .purpleColor()
}
}

class SwitchWithTextTableViewCell: UITableViewCell {
func configure(withDelegate delegate: SwitchWithTextCellProtocol)
{
}
}

struct MinionModeViewModel: SwitchWithTextCellProtocol {
var title = "Minion Mode!!!"
var switchOn = true
return .yellowColor()
}
func onSwitchTogleOn(on: Bool) {
if on {
print("The Minions are here to stay!")
} else {
print("The Minions went out to play!")
}
}
}

CELLFORROWATINDEXPATH
// YourViewController.swift
let cell = tableView.dequeueReusableCellWithIdentifier("SwitchWithTextTableViewCell",
forIndexPath: indexPath) as! SwitchWithTextTableViewCell
// this is where the magic happens!
cell.configure(withDelegate: MinionModeViewModel())
return cell

protocol SwitchWithTextCellDataSource {
var title: String { get }
}
protocol SwitchWithTextCellDelegate {
var textColor: UIColor { get }
var font: UIFont { get }
}

// SwitchWithTextTableViewCell
func configure(withDataSource dataSource: SwitchWithTextCellDataSource,
delegate: SwitchWithTextCellDelegate?)
{
}

struct MinionModeViewModel: SwitchWithTextCellDataSource {
var title = "Minion Mode!!!"
var switchOn = true
}

extension MinionModeViewModel: SwitchWithTextCellDelegate {
return .yellowColor()
}
if on {
} else {
}
}
}

// SettingsViewController
let viewModel = MinionModeViewModel()
cell.configure(withDataSource: viewModel, delegate: viewModel)
return cell

@MHOLLEMANS: MIXINS
AND TRAITS IN SWIFT 2.0

class AIPlayer: GameObject, AITrait, GunTrait, RenderTrait, HealthTrait {
...
}
class ZapMonster: GameObject, GunTrait, RenderTrait, HealthTrait, MovementTrait {
...
}

protocol TextPresentable {
var text: String { get }
var textColor: UIColor { get }
var font: UIFont { get }
}
protocol SwitchPresentable {
}

protocol ImagePresentable {
var imageName: String { get }
}
protocol TextFieldPresentable {
var placeholder: String { get }
var text: String { get }
func onTextFieldDidEndEditing(textField: UITextField)
}

extension TextPresentable {
var textColor: UIColor {
return .blackColor()
}
var font: UIFont {
return .systemFontOfSize(17)
}
}

!!!
class SwitchWithTextTableViewCell<T where T: TextPresentable, T: SwitchPresentable>: UITableViewCell {
private var delegate: T?
func configure(withDelegate delegate: T) {
}
}

extension MinionModeViewModel: TextPresentable {
var text: String { return "Minion Mode" }
var textColor: UIColor { return .blackColor() }
var font: UIFont { return .systemFontOfSize(17.0) }
}

extension MinionModeViewModel: SwitchPresentable {
var switchOn: Bool { return false }
var switchColor: UIColor { return .yellowColor() }
if on {
} else {
}
}
}

let cell = tableView.dequeueReusableCellWithIdentifier("SwitchWithTextTableViewCell",
forIndexPath: indexPath) as! SwitchWithTextTableViewCell<MinionModeViewModel>
let viewModel = MinionModeViewModel()
cell.configure(withDelegate: viewModel)
return cell

"Change is the only constant."
— Unknown

class SwitchWithTextTableViewCell<T where T: TextPresentable, T: SwitchPresentable, T: ImagePresentable>: UITableViewCell {
}

extension MinionModeViewModel: ImagePresentable {
var imageName: String { return "minionParty.png" }
}

> Use Protocols to Configure Your Views
> Use Protocol Extensions for Defaults
> Use ViewModels to Provide Data for the Protocols

Protocol-Oriented MVVM (extended edition)

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