Swift Combine

Publish

@objc
func startTimer() {
    print("Start")
    
    subscription = Timer
        .publish(every: 1, on: .main, in: .common)
        .autoconnect() // 连接???
        .scan(0, { (count, _) in  // 生成一个value, 这里跟reduce很像
            return count + 1
        })
        .sink(receiveCompletion: { completion in // 使用每次订阅到的value或事件
            switch completion {
                case .failure(let error):
                    print("Stream has failed with error: \(error)")
                case .finished:
                    print("Stream has completed")
            }
        }, receiveValue: { count in
            print("Updating the label to the current value: \(count.format)")
            self.countLbl.text = count.format
        })
}

@objc
func stopTimer() {
    print("Stop")
    subscription?.cancel()
}

publisher(不是publish), assing

final class LevelsManager {
    var level: Int = 0 {
        didSet {
            print("User's current level \(level)")
        }
    }
}

let lvlsManager = LevelsManager()
let lvlsRange = (0...100)
let cancellable = lvlsRange.
                publisher.
                assign(to: \.level, on: lvlsManager)

event

// notification, 从post变成了publisher

let subscription = NotificationCenter.default
    .publisher(for: .UIApplicationDidBecomeActive)
    .sink { _ in
        print("App is active")
    }

NotificationCenter.default
.publisher(for: UITextField.textDidChangedNotification, object: inputTextField)
.compactMap { ($0.object as? UITextField)?.text }
.map { "The user entered \($0)" }
//.sink { print($0) }
// 上面是sink, 下面是assign
.assign(to: \.text, on: label)
.store(in: $subscriptions) // 这里是设了个set用来存储
// var subscriptions = Set<AnyCancellable>()

可见没有像rxSwift一样的把事件直接pulish的用法, 而用notification来中转, 说明目前只扩展了notification吧

CurrentValue Subject

// 假设有一个对象/结构体
struct Personl{
    var firstName: String
    var lastName: String
    var occupation: string
}

extension Person{

    var message: String
        "\(firstName) \(lastName) is a \(occupation)"
    ｝

    var isValid: Bool{
        firstName.isEmpty && IlastName.isEmpty && loccupation.isEmpty
    }
}

// 你不能去new一个Person出来, 而是一个subject
private let person = CurrentValueSubject<Person， Error>(Person(firstName： "", LastName："", occupation：""))

// 用.value来使用(current subject)
NotificationCenter
 .default
 .publisher(for: UITextField.textDidChangeNotification, object: firstNameTxtField)
 .compactMap({ ($0.object as? UITextField)？.text  })
 .sink {［weak self］ val in
    self?.person.value.firstName = val // 这里
 }
 .store(in: &subscriptions)

 // person也是可以被监听的
 person.sink { _ in 
 
 } receiveValue: { p in 
    print(p)
 }
 .store(in: &subscriptions)

 // 发停止监听信号, 如点击完成时:
 func didClickConfirm() {
    person.send(completion: .finished)
 }

Passthrough Subjects

let subject = PassthroughSubject<String, Never>()

// passthrough subjects没有.value属性
// 意味着它只能通用sink来取值
subject.sink { value in
    print(value)
}

subject.send("Hello")
subject.send("World")

Multithread

final class IMageDownloaderViewMOdel {
    let image = PassthroughSubject<UIImage, Never>()
    var subscriptions =  Set<AnyCancellable>()

    func downloadImage(url: String) {
        URLSession.shared.dataTaskPublisher(for: URL(string: url)!)
        .subscribe(on: DispatchQueue.global(qos: .background))
        .map { UIImage(data: $0.data) }
        .receive(on: DispatchQueue.main)
        .handleEvent(receiveSubscription: { _ in
            print("Download started")
            rint("Start subscription on the main thread: \(Thread.isMainThread)")
        }, receiveOutput: { image in
            print("Downloaded image")
        }, receiveCompletion: { completion in
            print("Download completed")
        })
        .sink(receiveCompletion: { completion in
            print("Finished subscription on the main thread: \(Thread.isMainThread)")
            switch completion {
                case .failure(let error):
                    print("Stream has failed with error: \(error)")
                case .finished:
                    print("Stream has completed")
            }
        }, receiveValue: { [weak self] image in
            print("Recieved subscription on the main thread: \(Thread.isMainThread)")
            self?.image.send(image)
            self?.image.send(completion: .finished)
        })
        .store(in: &subscriptions)
    }
}

// binding
imgDownlloaderViewModel.image.assign(to: \.image, on: contentImageView)
.store(in: &subscriptions)

// trigger
imgDownloderViewModel.downloadImage(url: "https://www.example.com/image.jpg")

Memory Management

上面的例子中, 有个assign(to: on:)方法, assign给了self的一个属性, 这就造成了循环引用, 导致这个viewmodel不能被释放掉, 如果存在这种情况, 就不要偷懒了, 还是用sink方法, 在回调里用weak self.

SwiftUI

• 一个@Published属性, 就是一个CurrentValueSubject

自定义Publisher

网络请求转成publisher, 使用eraseToAnyPublisher

func request<T: Decodable>(url: URL) -> AnyPublisher<T, Error> {
    return URLSession.shared.dataTaskPublisher(for: url)
    .map(\.data)
    .decode(type: T.self, decoder: JSONDecoder())
    .eraseToAnyPublisher()
    .store(in: &subscriptions)
}

如果在里面catch了, 就可以返回AnyPublisher<T, Never>

Future, Defered

let future = Future<Int, Error> { promise in
    DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
        promise(.success(42))
    }
}

let publisher = future.eraseToAnyPublisher()

// deferred
let deferred = Deferred {
    Future<Int, Error> { promise in
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            promise(.success(42))
        }
    }
}

let publisher = deferred.eraseToAnyPublisher()