其實MVVM和Presentation Controls差不多就是一個概念，MVVM在網上隨便一搜就有很多教程。

接下來用一個例子來解說一下：

1.創建Trip類

class Trip {
//屬性
let departure: NSDate
let arrival: NSDate
let actualDeparture: NSDate
let delay: NSTimeInterval
let delayed: Bool
let duration: NSTimeInterval
//初始化方法
init(departure: NSDate, arrival: NSDate, actualDeparture: NSDate? = nil) {
    self.departure = departure
    self.arrival = arrival
    self.actualDeparture = actualDeparture ?? departure

    // 計算
    duration = self.arrival.timeIntervalSinceDate(self.departure)
    delay = self.actualDeparture.timeIntervalSinceDate(self.departure)
    delayed = delay > 0
}
}

2.創建TripViewModel類

class TripViewModel {

let date: String
let departure: String
let arrival: String
let duration: String
let delay: String?
let delayHidden: Bool
let departureTimeColor: UIColor

init(_ trip: Trip) {
    date = NSDateFormatter.localizedStringFromDate(trip.departure, dateStyle: .ShortStyle, timeStyle: .NoStyle)
    departure = NSDateFormatter.localizedStringFromDate(trip.departure, dateStyle: .NoStyle, timeStyle: .ShortStyle)
    arrival = NSDateFormatter.localizedStringFromDate(trip.arrival, dateStyle: .NoStyle, timeStyle: .ShortStyle)

    let durationFormatter = NSDateComponentsFormatter()
    durationFormatter.allowedUnits = [.Hour, .Minute]
    durationFormatter.unitsStyle = .Short
    duration = durationFormatter.stringFromTimeInterval(trip.duration)!

    delayHidden = !trip.delayed
    if trip.delayed {
        durationFormatter.unitsStyle = .Full
        delay = String.localizedStringWithFormat(NSLocalizedString("%@ delay", comment: "Show the delay"), durationFormatter.stringFromTimeInterval(trip.delay)!)
        departureTimeColor = .redColor()
    } else {
        self.delay = nil
        departureTimeColor = UIColor(red: 0, green: 0, blue: 0.4, alpha: 1)
    }
}
}

3.在viewcontrollers中使用viewmodel

class ViewController: UIViewController {

@IBOutlet weak var dateLabel: UILabel!
@IBOutlet weak var departureTimeLabel: UILabel!
@IBOutlet weak var arrivalTimeLabel: UILabel!
@IBOutlet weak var durationLabel: UILabel!
@IBOutlet weak var delayLabel: UILabel!

//初始化viewmodel
let tripModel = TripViewViewModel(Trip(departure: NSDate(timeIntervalSince1970: 1444396193), arrival: NSDate(timeIntervalSince1970: 1444397193), actualDeparture: NSDate(timeIntervalSince1970: 1444396493)))

override func viewDidLoad() {
    super.viewDidLoad()

    dateLabel.text = tripModel.date
    departureTimeLabel.text = tripModel.departure
    arrivalTimeLabel.text = tripModel.arrival
    durationLabel.text = tripModel.duration
    delayLabel.text = tripModel.delay
    delayLabel.hidden = tripModel.delayHidden
    departureTimeLabel.textColor = tripModel.departureTimeColor
}
}

用一個常量屬性來代替設置viewmodel，會通過prepareForSegue方法傳遞給控制器，這里已經是一個比較好的視圖控制器了，因為這里不包含任何數據傳遞邏輯給viewmodel。

4.使用Presentation controls代替viewmodel

class TripPresentationControl: NSObject {

@IBOutlet weak var dateLabel: UILabel!
@IBOutlet weak var departureTimeLabel: UILabel!
@IBOutlet weak var arrivalTimeLabel: UILabel!
@IBOutlet weak var durationLabel: UILabel!
@IBOutlet weak var delayLabel: UILabel!

var trip: Trip! {
    didSet {
        dateLabel.text = NSDateFormatter.localizedStringFromDate(trip.departure, dateStyle: .ShortStyle, timeStyle: .NoStyle)
        departureTimeLabel.text = NSDateFormatter.localizedStringFromDate(trip.departure, dateStyle: .NoStyle, timeStyle: .ShortStyle)
        arrivalTimeLabel.text  = NSDateFormatter.localizedStringFromDate(trip.arrival, dateStyle: .NoStyle, timeStyle: .ShortStyle)

        let durationFormatter = NSDateComponentsFormatter()
        durationFormatter.allowedUnits = [.Hour, .Minute]
        durationFormatter.unitsStyle = .Short
        durationLabel.text = durationFormatter.stringFromTimeInterval(trip.duration)!

        delayLabel.hidden = !trip.delayed
        if trip.delayed {
            durationFormatter.unitsStyle = .Full
            delayLabel.text = String.localizedStringWithFormat(NSLocalizedString("%@ delay", comment: "Show the delay"), durationFormatter.stringFromTimeInterval(trip.delay)!)
            departureTimeLabel.textColor = .redColor()
        }
    }
}
}
class ViewController: UIViewController {

@IBOutlet var tripPresentationControl: TripPresentationControl!

let trip = Trip(departure: NSDate(timeIntervalSince1970: 1444396193), arrival: NSDate(timeIntervalSince1970: 1444397193), actualDeparture: NSDate(timeIntervalSince1970: 1444396493))

override func viewDidLoad() {
    super.viewDidLoad()

    tripPresentationControl.trip = trip
}
}

是不是這樣看上去更清楚了。

5.優化一下

// 使用結構體
struct TripViewModel {

let date: String
let departure: String
let arrival: String
let duration: String
let delay: String?
let delayHidden: Bool
let departureTimeColor: UIColor 
init(date: String, departure: String, arrival: String, 
    duration: String, delay: String?, delayHidden: Bool, 
    departureTimeColor: UIColor) {

    self.date = date
    self.departure = departure
    self.arrival = arrival
    self.duration = duration
    self.delay = delay
    self.delayHidden = delayHidden
    self.departureTimeColor = departureTimeColor
}
}
class TripPresentationControl: NSObject {

@IBOutlet weak var dateLabel: UILabel!
@IBOutlet weak var departureTimeLabel: UILabel!
@IBOutlet weak var arrivalTimeLabel: UILabel!
@IBOutlet weak var durationLabel: UILabel!
@IBOutlet weak var delayLabel: UILabel!

var tripViewModel: TripViewModel! {
    didSet {
        dateLabel.text = tripViewModel.date
        departureTimeLabel.text = tripViewModel.departure
        arrivalTimeLabel.text = tripViewModel.arrival
        durationLabel.text = tripViewModel.duration

        let hideDelay = tripViewModel.delayHidden
        delayLabel.hidden = hideDelay
        
        if let delayText = tripViewModel.delay where !hideDelay {
            durationFormatter.unitsStyle = .Full
            delayLabel.text = delayText
            departureTimeLabel.textColor = tripViewModel.departureTimeColor
        }
    }
}
}
class ViewController: UIViewController {

@IBOutlet var tripPresentationControl: TripPresentationControl!

var tripViewModel: TripViewModel!

override func viewDidLoad() {
    super.viewDidLoad()

    tripPresentationControl.tripViewModel = tripViewModel
}
}
//進行擴展
extension TripViewModel {

init(_ trip: Trip) {
    date = NSDateFormatter.localizedStringFromDate(trip.departure, dateStyle: .ShortStyle, timeStyle: .NoStyle)
    departure = NSDateFormatter.localizedStringFromDate(trip.departure, dateStyle: .NoStyle, timeStyle: .ShortStyle)
    arrival = NSDateFormatter.localizedStringFromDate(trip.arrival, dateStyle: .NoStyle, timeStyle: .ShortStyle)

    let durationFormatter = NSDateComponentsFormatter()
    durationFormatter.allowedUnits = [.Hour, .Minute]
    durationFormatter.unitsStyle = .Short
    duration = durationFormatter.stringFromTimeInterval(trip.duration)!

    delayHidden = !trip.delayed
    if trip.delayed {
        durationFormatter.unitsStyle = .Full
        delay = String.localizedStringWithFormat(NSLocalizedString("%@ delay", comment: "Show the delay"), durationFormatter.stringFromTimeInterval(trip.delay)!)
        departureTimeColor = .redColor()
    } else {
        self.delay = nil
        departureTimeColor = UIColor(red: 0, green: 0, blue: 0.4, alpha: 1)
    }
}
}  
class ShowExistingTrip {

let view: ViewController

init(view: ViewController) {
    
    self.view = view
}

看客肯定臭罵偶一頓，臥槽，全是code。