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just

代码示例, Just:

使用 Subscribers.Sink

先声明再组装的方式：

swift

let mySubjuect = Just(4)
let subscriber = Subscribers.Sink<Int, Never /*never表示没有数据类型*/ > { finish in
    if finish == .finished {
        print("success")
    } else { // 不会执行，just无错误        
        print("error")
    }
} receiveValue: { value in
    print(value)
}
let subscriber1 = Subscribers.Sink<Int, Never /*never表示没有数据类型*/ > { finish in
} receiveValue: { value in
    print(value)
}
mySubjuect.receive(subscriber: subscriber)
mySubjuect.receive(subscriber: subscriber1)

let mySubjuect = Just(4)
let subscriber = Subscribers.Sink<Int, Never /*never表示没有数据类型*/ > { finish in
    if finish == .finished {
        print("success")
    } else { // 不会执行，just无错误        
        print("error")
    }
} receiveValue: { value in
    print(value)
}
let subscriber1 = Subscribers.Sink<Int, Never /*never表示没有数据类型*/ > { finish in
} receiveValue: { value in
    print(value)
}
mySubjuect.receive(subscriber: subscriber)
mySubjuect.receive(subscriber: subscriber1)

使用 .publisher 与 .sink

也可以将数组、区间等通过.publisher语法作为一个发布者。
sink相关方法有：

.sink(receiveValue: closure)
- 仅关注结果输出
sink(receiveCompletion:closure, receiveValue:closure) ：
- 可以获取结束状态

swift

let range: ClosedRange<Int> = 0 ... 3
    // 专注于结果输出
_ = range.publisher
    .sink { value in
        print(value) // 0 1 2 3
    }
    // 可以获取结束状态
_ = range.publisher.sink { completion in
    if completion == .finished {
        print("completion")
    }
} receiveValue: { element in
    print("element", element)
}

let range: ClosedRange<Int> = 0 ... 3
    // 专注于结果输出
_ = range.publisher
    .sink { value in
        print(value) // 0 1 2 3
    }
    // 可以获取结束状态
_ = range.publisher.sink { completion in
    if completion == .finished {
        print("completion")
    }
} receiveValue: { element in
    print("element", element)
}

assign

keyPath

assign可以通过keyPath的方式给模型赋值：

swift

class User {
    var name: String = ""
}
let user = User()
let cancelable = ["吴彦祖"].publisher.assign(to: \.name, on: user)
print(user.name) // 吴彦祖

class User {
    var name: String = ""
}
let user = User()
let cancelable = ["吴彦祖"].publisher.assign(to: \.name, on: user)
print(user.name) // 吴彦祖

assign 与 @Published

swift

class MyModel: ObservableObject {
    @Published var id: Int = 0
}

let model = MyModel()
Just(100).assign(to: &model.$id)
print(model.id)

_ = Just(200).assign(to: \.id, on: model)
print(200)

class MyModel: ObservableObject {
    @Published var id: Int = 0
}

let model = MyModel()
Just(100).assign(to: &model.$id)
print(model.id)

_ = Just(200).assign(to: \.id, on: model)
print(200)

上述写法在SwiftUI里面随处可见

https://devv.ai/zh/search?threadId=d98yqg2heiv4

@Published 修饰后，可以简化assign的操作
上述示例代码中ObservableObject也可以去掉，在 SwiftUI 中，@ObservableObject 用于标记一个类，该类可以存储数据并在更改时触发视图更新。而 @Published 则用于标记可观察对象中应该在更改时触发视图更新的属性。

[iOS][Swift]CombineでUIKitのUI更新を実装してみる #Swift - Qiita

future

swift

let future = Future<Int, Never> { promise in
    // 此处可执行耗时操作
    promise(.success(200))
}
let subscribe = Subscribers.Sink<Int, Never> { statue in
    if statue == .finished {
        print("finished")
    }
} receiveValue: { value in
    print(value)
}
future.subscribe(subscribe)

let future = Future<Int, Never> { promise in
    // 此处可执行耗时操作
    promise(.success(200))
}
let subscribe = Subscribers.Sink<Int, Never> { statue in
    if statue == .finished {
        print("finished")
    }
} receiveValue: { value in
    print(value)
}
future.subscribe(subscribe)

operator

swift

let publisher = Just(5)
let tranform = Publishers.Map<Just<Int>, String>.init(upstream: publisher) { value in
    "字符串值：\(value)"
}

let subscribe = Subscribers.Sink<String, Never>.init { _ in
} receiveValue: { value in
    print(value) // 字符串值：5
}
tranform.subscribe(subscribe)
// 不声明`subscribe`,直接使用也可以
// tranform.sink { value in
//    print(value)
// }

let publisher = Just(5)
let tranform = Publishers.Map<Just<Int>, String>.init(upstream: publisher) { value in
    "字符串值：\(value)"
}

let subscribe = Subscribers.Sink<String, Never>.init { _ in
} receiveValue: { value in
    print(value) // 字符串值：5
}
tranform.subscribe(subscribe)
// 不声明`subscribe`,直接使用也可以
// tranform.sink { value in
//    print(value)
// }

简化写法:

swift

let publisher = Just(5)
_ = publisher.map { value in
    "-> String Value: \(value)"
}.sink { value in
    print(value)
}

// 示例2： 
let publisher = Just(5)
_ = publisher
	.filter { item in
		item >= 5
	}
	.map { value in
		"-> String Value: \(value)"
	}.sink { value in
		print(value)
	}

let publisher = Just(5)
_ = publisher.map { value in
    "-> String Value: \(value)"
}.sink { value in
    print(value)
}

// 示例2： 
let publisher = Just(5)
_ = publisher
	.filter { item in
		item >= 5
	}
	.map { value in
		"-> String Value: \(value)"
	}.sink { value in
		print(value)
	}

CurrentValueSubject

CurrentValueSubject(value) 可以保存和发布最后的数据（来自send方法和其他发布者）,可设置默认数据。可以类比RxSwift中的BehaviorRelay

swift

let publisher = CurrentValueSubject<Int, Never>(20)
let subscribe = Subscribers.Sink<Int, Never>.init { _ in
} receiveValue: { value in
    print("here: \(value)")
}

publisher.subscribe(subscribe)

var cancellables = Set<AnyCancellable>()
publisher.sink { value in
    print("there", value)
}.store(in: &cancellables)
// 此处必须加 `.store(in: )` , 否则只会执行一次。 因为执行一次后就被释放，不会持续接收事件

publisher.send(21)
publisher.send(22)
//输出：
//here: 20
//there 20
//there 21
//heare: 21
//there 22
//here: 22

let publisher = CurrentValueSubject<Int, Never>(20)
let subscribe = Subscribers.Sink<Int, Never>.init { _ in
} receiveValue: { value in
    print("here: \(value)")
}

publisher.subscribe(subscribe)

var cancellables = Set<AnyCancellable>()
publisher.sink { value in
    print("there", value)
}.store(in: &cancellables)
// 此处必须加 `.store(in: )` , 否则只会执行一次。 因为执行一次后就被释放，不会持续接收事件

publisher.send(21)
publisher.send(22)
//输出：
//here: 20
//there 20
//there 21
//heare: 21
//there 22
//here: 22

swiftui中使用的例子：

swift

import SwiftUI
import Combine

// 创建一个CurrentValueSubject对象
class DataModel: ObservableObject {
    var currentValueSubject = CurrentValueSubject<Int, Never>(0)    
    func updateValue(newValue: Int) {
        currentValueSubject.send(newValue)
    }
}

// SwiftUI视图
struct ContentView: View {
    @StateObject var dataModel = DataModel()
    
    var body: some View {
        VStack {
            Text("Current Value: \(dataModel.currentValueSubject.value)")
                .padding()
            
            Button("Update Value") {
                dataModel.updateValue(newValue: Int.random(in: 1...100))
            }
        }
    }
}

// 在ContentView中订阅CurrentValueSubject对象
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

import SwiftUI
import Combine

// 创建一个CurrentValueSubject对象
class DataModel: ObservableObject {
    var currentValueSubject = CurrentValueSubject<Int, Never>(0)    
    func updateValue(newValue: Int) {
        currentValueSubject.send(newValue)
    }
}

// SwiftUI视图
struct ContentView: View {
    @StateObject var dataModel = DataModel()
    
    var body: some View {
        VStack {
            Text("Current Value: \(dataModel.currentValueSubject.value)")
                .padding()
            
            Button("Update Value") {
                dataModel.updateValue(newValue: Int.random(in: 1...100))
            }
        }
    }
}

// 在ContentView中订阅CurrentValueSubject对象
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

代码示例：发送失败消息以终止，再往后的消息不会收到

swift

var cancellables = Set<AnyCancellable>()
let publisher = CurrentValueSubject<Int, MyError>(20)
let subscribe = Subscribers.Sink<Int, MyError>.init { ff in
    if ff == .finished {
        print("finished")
    } else {
        print("error")
    }
    switch ff {
    case .finished:
        print("finished")
    case .failure(let err):
        print(err)
    }
} receiveValue: { value in
    print("here: \(value)")
}

publisher.subscribe(subscribe)

publisher.send(1)
publisher.send(2)
publisher.send(3)
publisher.send(completion: .failure(.uploadFailed))
publisher.send(4)
// here: 20
// here: 1
// here: 2
// here: 3
// error
// uploadFailed

var cancellables = Set<AnyCancellable>()
let publisher = CurrentValueSubject<Int, MyError>(20)
let subscribe = Subscribers.Sink<Int, MyError>.init { ff in
    if ff == .finished {
        print("finished")
    } else {
        print("error")
    }
    switch ff {
    case .finished:
        print("finished")
    case .failure(let err):
        print(err)
    }
} receiveValue: { value in
    print("here: \(value)")
}

publisher.subscribe(subscribe)

publisher.send(1)
publisher.send(2)
publisher.send(3)
publisher.send(completion: .failure(.uploadFailed))
publisher.send(4)
// here: 20
// here: 1
// here: 2
// here: 3
// error
// uploadFailed

@Published 和 CurrentValueSubject 之间还有一些区别和优势。
错误类型：@Published 的发布者的错误类型是 Never，而 CurrentValueSubject 可以指定错误类型。
使用范围：@Published 只能在类中使用，而 CurrentValueSubject 可以在任何地方使用，包括结构体和枚举。
订阅者行为：@Published 不能直接用作订阅者，而 CurrentValueSubject 可以直接订阅。
协议声明：@Published 不能在协议声明中使用，而 CurrentValueSubject 可以在协议中声明并使用。
设置初始值：CurrentValueSubject 可以在初始化时设置初始值，而 @Published 需要在声明时设置初始值。
总的来说，@Published 更适合简单的自动更新视图的场景

PassthroughSubject

和CurrentValueSubject的区别是没有默认值：

swift

let publisher = PassthroughSubject<Int, Never>()
// 写法1
let subscribe = Subscribers.Sink<Int, Never>.init { _ in
} receiveValue: { value in
    print("here: \(value)")
}

publisher.subscribe(subscribe)

// 写法2
var cancellables = Set<AnyCancellable>()
publisher.sink { value in
    print("there", value)
}.store(in: &cancellables)

publisher.send(21)
publisher.send(22)

let publisher = PassthroughSubject<Int, Never>()
// 写法1
let subscribe = Subscribers.Sink<Int, Never>.init { _ in
} receiveValue: { value in
    print("here: \(value)")
}

publisher.subscribe(subscribe)

// 写法2
var cancellables = Set<AnyCancellable>()
publisher.sink { value in
    print("there", value)
}.store(in: &cancellables)

publisher.send(21)
publisher.send(22)

Swift Combine

UI组件

使用总结

官方教程

Combine之基本的订阅者和发布者代码示例

just

使用 Subscribers.Sink

使用 .publisher 与 .sink

assign

keyPath

assign 与 @Published

future

operator

CurrentValueSubject

PassthroughSubject

Combine之基本的订阅者和发布者代码示例

just ​

使用 Subscribers.Sink ​

使用 .publisher 与 .sink ​

assign ​

keyPath ​

assign 与 @Published ​

future ​

operator ​

CurrentValueSubject ​

PassthroughSubject ​

just

使用 Subscribers.Sink

使用 .publisher 与 .sink

assign

keyPath

assign 与 @Published

future

operator

CurrentValueSubject

PassthroughSubject