😭 🤸🏾 🐋 被黑扩展中可用的MVVM 🤘🏻 👩🏿‍🤝‍👨🏽 ⛩️

多年来，除其他外，我一直参与在我的工作项目中（而不是在如此工作的项目中）设置MVVM。我在模式固有的Windows项目中表现出了极大的热情。出于值得更好使用的热情，我在MVVM未能扎根的iOS项目中做到了这一点。

, , , - , .

- — , , MVVM . : , MVC MVVM .

, MVVM , , . MVVM. , Microsoft, , . , . , - , .

, , :

. .
. , .
. , SOLID, SOLID.
. , .

, , .

1. DI
2. MVVM
- <=
- ( )
3.

MVVM , . , . - MVVM , . , «» .

, — . , , , .

OrdersVC	- . , iOS — -. , -.
OrdersView	OrdersVC. — VC View , . OrdersView — , , ,
OrdersVM	OrdersVC, , . OrdersProvider -
Order	, , .
OrderCell	UITableView,
OrderVM	OrderCell. Order,
OrdersProvider	, — , , — .

, MVVM , , iOS, MVC, - . , , — View, iOS .

: , View, , .

, View ViewModel, : -, . . MVVM, : View viewModel:

protocol IHaveViewModel: AnyObject {
    associatedtype ViewModel

    var viewModel: ViewModel? { get set }
    func viewModelChanged(_ viewModel: ViewModel)
}

I interface. -, , . , .

, viewModel . - , viewModelChanged(_:), . IHaveViewModel OrderCell — OrderVM :

final class OrderCell: UITableViewCell, IHaveViewModel {
    var viewModel: OrderVM? {
        didSet {
            guard let viewModel = viewModel else { return }
            viewModelChanged(viewModel)
        }
    }

    func viewModelChanged(_ viewModel: OrderVM) {
        textLabel?.text = viewModel.name
    }
}

, , textLabel . , :

final class OrderVM {
    let order: Order
    var name: String {
        return "\(order.name) #\(order.id)"
    }
    init(order: Order) {
        self.order = order
    }
}

, viewModel , , . OrderCell , :

tableView(_:cellForRowAt:) dequeueReusableCell(withIdentifier:for:) UITableViewCell.
IHaveViewModel, viewModel -.
, , 2, .
Protocol 'IHaveViewModel' can only be used as a generic constraint because it has Self or associated type requirements.

, (type erasure). . , — (shadow type erasure). ? , :

protocol IHaveAnyViewModel: AnyObject {
    var anyViewModel: Any? { get set }
}

, . IHaveViewModel , :

protocol IHaveViewModel: IHaveAnyViewModel {
    associatedtype ViewModel

    var viewModel: ViewModel? { get set }
    func viewModelChanged(_ viewModel: ViewModel)
}

OrderCell :

final class OrderCell: UITableViewCell, IHaveViewModel {
    typealias ViewModel = OrderVM

    var anyViewModel: Any? {
        didSet {
            guard let viewModel = anyViewModel as? ViewModel else { return }
            viewModelChanged(viewModel)
        }
    }

    var viewModel: ViewModel? {
        get {
            return anyViewModel as? ViewModel
        }
        set {
            anyViewModel = newValue
        }
    }

    func viewModelChanged(_ viewModel: ViewModel) {
        textLabel?.text = viewModel.name
    }
}

anyViewModel, , . IHaveAnyViewModel -. viewModel, -, , , viewModelChanged(_:) .

, MVVM : . , - IHaveViewModel, , , . , , IHaveViewModel.

(extensions) : . , , , , .

, IHaveViewModel, extensions must not contain stored properties:

extension IHaveViewModel {
    var anyViewModel: Any? //   :(
}

, , . .

, , . , extensions must not contain stored properties , , , . , , Objective-C-. , , :

private var viewModelKey: UInt8 = 0

extension IHaveViewModel {

    var anyViewModel: Any? {
        get {
            return objc_getAssociatedObject(self, &viewModelKey)
        }
        set {
            let viewModel = newValue as? ViewModel

            objc_setAssociatedObject(self, 
                &viewModelKey, 
                viewModel, 
                .OBJC_ASSOCIATION_RETAIN_NONATOMIC)

            if let viewModel = viewModel {
                viewModelChanged(viewModel)
            }
    }

    var viewModel: ViewModel? {
        get {
            return anyViewModel as? ViewModel
        }
        set {
            anyViewModel = newValue
        }
    }

    func viewModelChanged(_ viewModel: ViewModel) {

    }
}

, . : objc_getAssociatedObject objc_setAssociatedObject, .

, . , viewModelKey. OrderCell :

final class OrderCell: UITableViewCell, IHaveViewModel {
    typealias ViewModel = OrderVM

    func viewModelChanged(_ viewModel: OrderVM) {
        textLabel?.text = viewModel.name
    }
}

, , , . Objective-C- — . , .

( )

IHaveViewModel OrdersVC — OrdersVM. - :

final class OrdersVM {
    var orders: [OrderVM] = []

    private var ordersProvider: OrdersProvider

    init(ordersProvider: OrdersProvider) {
        self.ordersProvider = ordersProvider
    }

    func loadOrders() {
        ordersProvider.loadOrders() { [weak self] model in
            self?.orders = model.map { OrderVM(order: $0) }
        }
    }
}

OrdersVM OrdersProvider . OrdersProvider loadOrders(completion:):

struct Order {
    let name: String
    let id: Int
}

final class OrdersProvider {
    func loadOrders(completion: @escaping ([Order]) -> Void) {
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            completion((0...99).map { Order(name: "Order", id: $0) })
        }
    }
}

, , -:

final class OrdersVC: UIViewController, IHaveViewModel {
    typealias ViewModel = OrdersVM

    private lazy var tableView = UITableView()

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.dataSource = self
        tableView.register(OrderCell.self, forCellReuseIdentifier: "order")
        view.addSubview(tableView)

        viewModel?.loadOrders()
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        tableView.frame = view.bounds
    }

    func viewModelChanged(_ viewModel: OrdersVM) {
        tableView.reloadData()
    }
}

viewDidLoad() loadOrders() -, . - viewModelChanged(_:), . :

extension OrdersVC: UITableViewDataSource {
    func tableView(_ tableView: UITableView, 
        numberOfRowsInSection section: Int) -> Int {

        return viewModel?.orders.count ?? 0
    }

    func tableView(_ tableView: UITableView, 
        cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCell(withIdentifier: "order", 
            for: indexPath)

        if let cell = cell as? IHaveAnyViewModel {
            cell.anyViewModel = viewModel?.orders[indexPath.row]
        }
        return cell
    }
}

, IHaveAnyViewModel, , - . . , :

let viewModel = OrdersVM(ordersProvider: OrdersProvider())
let viewController = OrdersVC()
viewController.viewModel = viewModel

OrdersVC , . , , , .

, loadOrders(completion:) , viewDidLoad(), , reloadData() orders . , — -.

MVVM , ViewModel View. View — , . - , View - . View, - , . View, , , ViewModel View.

iOS- : . , MVVM Rx. MVVM . .NET — — INotifyPropertyChanged, ViewModel, — View.

, , . , , . . , , . RxSwift , Combine — iOS 13.

, , , , iOS .NET. ViewModel.

.NET — «», : , c -. , , , , - ViewController, View.

Swift : , , NotificationCenter. , , . :

final class Weak<T: AnyObject> {

    private let id: ObjectIdentifier?
    private(set) weak var value: T?

    var isAlive: Bool {
        return value != nil
    }

    init(_ value: T?) {
        self.value = value
        if let value = value {
            id = ObjectIdentifier(value)
        } else {
            id = nil
        }
    }
}

, , . - nil, ObjectIdentifier , Hashable:

extension Weak: Hashable {
    static func == (lhs: Weak<T>, rhs: Weak<T>) -> Bool {
        return lhs.id == rhs.id
    }

    func hash(into hasher: inout Hasher) {
        if let id = id {
            hasher.combine(id)
        }
    }
}

Weak<T>, :

final class Event<Args> {
    //         
    private var handlers: [Weak<AnyObject>: (Args) -> Void] = [:]

    func subscribe<Subscriber: AnyObject>(
        _ subscriber: Subscriber,
        handler: @escaping (Subscriber, Args) -> Void) {

        //  
        let key = Weak<AnyObject>(subscriber)
        //      ,    
        handlers = handlers.filter { $0.key.isAlive }
        //   
        handlers[key] = {
            [weak subscriber] args in
            //       ,
            //    
            guard let subscriber = subscriber else { return }
            handler(subscriber, args)
        }
    }

    func unsubscribe(_ subscriber: AnyObject) {
        //   ,     
        let key = Weak<AnyObject>(subscriber)
        handlers[key] = nil
    }

    func raise(_ args: Args) {
        //      
        let aliveHandlers = handlers.filter { $0.key.isAlive }
        //         
        aliveHandlers.forEach { $0.value(args) }
    }
}

, , , . Weak<T>, , , , — .

, , . Event<Args> subscribe(_:handler:) unsubscribe(_:). ( -) - , raise(_:).

, Void :

extension Event where Args == Void {
    func subscribe<Subscriber: AnyObject>(
        _ subscriber: Subscriber,
        handler: @escaping (Subscriber) -> Void) {

        subscribe(subscriber) { this, _ in
            handler(this)
        }
    }

    func raise() {
        raise(())
    }
}

. , - :

let event = Event<Void>()
event.raise() // -  ,

. , , weak self, :

event.subscribe(self) { this in
    this.foo() //   
}

, :

event.unsubscribe(self) //

! , . , , MVVM . .

OrdersVM OrdersVC , - . , , -, , . Objective-C-, :

private var changedEventKey: UInt8 = 0

protocol INotifyOnChanged {
    var changed: Event<Void> { get }
}

extension INotifyOnChanged {
    var changed: Event<Void> {
        get {
            if let event = objc_getAssociatedObject(self, 
                &changedEventKey) as? Event<Void> {
                return event
            } else {
                let event = Event<Void>()
                objc_setAssociatedObject(self, 
                    &changedEventKey, 
                    event, 
                    .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
                return event
            }
        }
    }
}

INotifyOnChanged - changed. INotifyOnChanged IHaveViewModel : - viewModelChanged(_:) :

extension IHaveViewModel {
    var anyViewModel: Any? {
        get {
            return objc_getAssociatedObject(self, &viewModelKey)
        }
        set {
            (anyViewModel as? INotifyOnChanged)?.changed.unsubscribe(self)
            let viewModel = newValue as? ViewModel

            objc_setAssociatedObject(self, 
                &viewModelKey, 
                viewModel, 
                .OBJC_ASSOCIATION_RETAIN_NONATOMIC)

            if let viewModel = viewModel {
                viewModelChanged(viewModel)
            }

            (viewModel as? INotifyOnChanged)?.changed.subscribe(self) { this in
                if let viewModel = viewModel {
                    this.viewModelChanged(viewModel)
                }
            }
        }
    }
}

, , :

final class OrdersVM: INotifyOnChanged {
    var orders: [OrderVM] = []

    private var ordersProvider: OrdersProvider

    init(ordersProvider: OrdersProvider) {
        self.ordersProvider = ordersProvider
    }

    func loadOrders() {
        ordersProvider.loadOrders() { [weak self] model in
            self?.orders = model.map { OrderVM(name: $0.name) }
            self?.changed.raise() // !
        }
    }
}

, — Weak<T>, Event<Args>, INotifyOnChanged , — , -: changed.raise().

raise(), , , , viewModelChanged(_:), , .

One More Thing:

INotifyOnChanged changed - . , , — , , — View - ViewModel? , - myPropertyChanged, — .

, Apple?

, , , , .

property wrapper, , wrappedValue , , @propertyWrapper. , , «» projectedValue. , , , , :

@propertyWrapper
struct Observable<T> {
    let projectedValue = Event<T>()

    init(wrappedValue: T) {
        self.wrappedValue = wrappedValue
    }

    var wrappedValue: T {
        didSet {
            projectedValue.raise(wrappedValue)
        }
    }
}

Observable. projectedValue. , wrappedValue. , , didSet.

Observable<T>, :

@Observable
var orders: [OrderVM] = []

, :

private var _orders = Observable<[OrderVM]>(wrappedValue: [])

var orders: [OrderVM] {
  get { _orders.wrappedValue }
  set { _orders.wrappedValue = newValue }
}

var $orders: Event<[OrderVM]> {
  get { _orders.projectedValue }
}

, , orders, wrappedValue, $orders, projectedValue. projectedValue — , orders :

viewModel.$orders.subscribe(self) { this, orders in
    this.update(with: orders)
}

! 15 Published Combine Apple, .

, Objective-C-. , , MVVM iOS. , , , .NET. iOS-, shadow type erasure property wrappers projected value.

Swift Playground.

被黑扩展中可用的MVVM

( )

One More Thing:

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