MVP Architecture

MVP is an architectural pattern, a derivation of the Model–View–Controller. It’s represented by three distinct components: Model, View and the Presenter. It was engineered to facilitate automated unit testing and improve the separation of concerns in presentation logic.

In examples you’ll find a simple project built with MVP pattern in mind.

Dog.swift

import Foundation

enum Breed: String {
    case bulldog  = "Bulldog"
    case doberman = "Doberman"
    case labrador = "Labrador"
}

struct Dog {
    let name:  String
    let breed: String
    let age:   Int
}

DoggyService.swift

import Foundation

typealias Result = ([Dog]) -> Void

class DoggyService {

    func deliverDoggies(_ result: @escaping Result) {

        let firstDoggy  = Dog(name: "Alfred", breed: Breed.labrador.rawValue, age: 1)
        let secondDoggy = Dog(name: "Vinny",  breed: Breed.doberman.rawValue, age: 5)
        let thirdDoggy  = Dog(name: "Lucky",  breed: Breed.labrador.rawValue, age: 3)

        let delay = DispatchTime.now() + Double(Int64(Double(NSEC_PER_SEC)*2)) / Double(NSEC_PER_SEC)

        DispatchQueue.main.asyncAfter(deadline: delay) {
            result([firstDoggy,
                    secondDoggy,
                    thirdDoggy])
        }
    }
}

DoggyPresenter.swift

import Foundation

class DoggyPresenter {

    // MARK: - Private
    fileprivate let dogService: DoggyService
    weak fileprivate var dogView: DoggyView?

    init(dogService: DoggyService){
        self.dogService = dogService
    }

    func attachView(_ attach: Bool, view: DoggyView?) {
        if attach {
            dogView = nil
        } else {
            if let view = view { dogView = view }
        }
    }

    func getDogs(){
        self.dogView?.startLoading()

        dogService.deliverDoggies { [weak self] doggies in
            self?.dogView?.finishLoading()

        if doggies.count == 0 {
            self?.dogView?.setEmpty()
        } else {
            self?.dogView?.setDoggies(doggies.map {
                return DoggyViewData(name: "\($0.name) \($0.breed)",
                                      age: "\($0.age)")
                })
            }
        }
    }
}

struct DoggyViewData {
    let name: String
    let age:  String
}

DoggyView.swift

import Foundation

protocol DoggyView: NSObjectProtocol {
    func startLoading()
    func finishLoading()
    func setDoggies(_ doggies: [DoggyViewData])
    func setEmpty()
}

DoggyListViewController.swift

import UIKit

class DoggyListViewController: UIViewController, UITableViewDataSource {

    @IBOutlet weak var emptyView: UIView?
    @IBOutlet weak var tableView: UITableView?
    @IBOutlet weak var spinner:   UIActivityIndicatorView?

    fileprivate let dogPresenter = DoggyPresenter(dogService: DoggyService())
    fileprivate var dogsToDisplay = [DoggyViewData]()

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView?.dataSource = self
        spinner?.hidesWhenStopped = true
        dogPresenter.attachView(true, view: self)
        dogPresenter.getDogs()
    }

    // MARK: DataSource
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return dogsToDisplay.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = UITableViewCell(style: .subtitle, reuseIdentifier: "Cell")
        let userViewData = dogsToDisplay[indexPath.row]
        cell.textLabel?.text = userViewData.name
        cell.detailTextLabel?.text = userViewData.age
        return cell
    }
}

extension DoggyListViewController: DoggyView {

    func startLoading() {
        spinner?.startAnimating()
    }

    func finishLoading() {
        spinner?.stopAnimating()
    }

    func setDoggies(_ doggies: [DoggyViewData]) {
        dogsToDisplay = doggies
        tableView?.isHidden = false
        emptyView?.isHidden = true;
        tableView?.reloadData()
    }

    func setEmpty() {
        tableView?.isHidden = true
        emptyView?.isHidden = false;
    }
}

Remarks

Components:

• Model is an interface responsible for the domain data (to be displayed or otherwise acted upon in the GUI)
• View is responsible for the presentation layer (GUI)
• Presenter is the “middle-man” between Model and View. It reacts to the user’s actions performed on the View, retrieves data from the Model, and formats it for display in the View

Component duties:

|Model|View|Presenter |---|---|---|---|---|---|---|---|---|--- |Communicates with DB layer|Renders data|Performs queries to the Model |Raising appropriate events|Receives events|Formats data from Model ||Very basic validation logic|Sends formatted data to the View |||Complex validation logic |||

Differences between MVC and MVP:

• View in MVC is tightly coupled with the Controller, the View part of the MVP consists of both UIViews and UIViewController
• MVP View is as dumb as possible and contains almost no logic (like in MVVM), MVC View has some business logic and can query the Model
• MVP View handles user gestures and delegates interaction to the Presenter, in MVC the Controller handles gestures and commands Model
• MVP pattern highly supports Unit Testing, MVC has limited support
• MVC Controller has lots of UIKit dependencies, MVP Presenter has none

Pros:

• MVP makes UIViewController a part of the View component it’s dumb, passive and…less massive ;]
• Most of the business logic is incapsulated due to the dumb Views, this gives an excellent testability. Mock objects can be introduced to test the domain part.
• Separated entities are easier to keep in head, responsibilities are clearly divided.

Cons

• You will write more code.
• Barrier for unexperienced developers or for those who don’t yet work with the pattern.