发布者(Publisher)与订阅者(Subscriber)

在 Combine 中，有几个重要的组成部分：

发布者：Publisher
订阅者：Subscriber
操作符：Operator

如果您熟悉观察者设计模式，那么Publisher就类似于Observable，Subscriber类似于Observer。

Example 1

Just只发布一个值即完成,Just可以认为是函数响应式编程中的Hello World，它很好的展示了Publisher与Subscriber是如何配合完成整个发布订阅过程的。

// 使用Just生成一个Publisher
let publisher1 = Just(42)

// 使用sink操作符生成订阅回调
let subscription1 = publisher1.sink { value in
    print("Received value from publisher1: \(value)")
}

Example 2

发布一系列的值

let publisher2 = [1,2,3,4,5].publisher

let subscription2 = publisher2
    .sink { value in
        print("Received value from publisher2: \(value)")
    }

输出：

Received value from publisher2: 1
Received value from publisher2: 2
Received value from publisher2: 3
Received value from publisher2: 4
Received value from publisher2: 5

Example 3

将上例中发布者publisher2发布的值赋值给类实例的属性

class MyClass {
    var property: Int = 0 {
        didSet {
            print("Did set property to \(property)")
        }
    }
}

let object = MyClass()
let subscription3 = publisher2.assign(to: \.property, on: object)

输出：

Did set property to 1
Did set property to 2
Did set property to 3
Did set property to 4
Did set property to 5

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