如何订阅

本小节，我们将试着使用PassthroughSubject完成一个发布订阅过程

步骤一：自定义一个错误类型

enum ExampleError: Swift.Error {
    case somethingWentWrong
}

步骤二：使用PassthroughSubject作为发布者，PassthroughSubject包含两个参数，第一个是发布的数据类型，第二个是错误类型

let subject = PassthroughSubject<String, ExampleError>()

subject.handleEvents(receiveSubscription: { (subscription) in
        print("New subscription!")
    }, receiveOutput: { _ in
        print("Received new value!")
    }, receiveCompletion: { _ in
        print("A subscription completed")
    }, receiveCancel: {
        print("A subscription cancelled")
    })
    .replaceError(with: "Failure")
    .sink { (value) in
        print("Subscriber received value: \(value)")
    }

步骤三：使用send函数发送数据

send常用函数

send(input:String）函数向该subject添加新值
send(completion:.finished)发送完成
send(completion: someError)发送error

subject.send("Hello!")
subject.send("Hello again!")
subject.send("Hello for the last time!")
subject.send(completion: .failure(.somethingWentWrong))
subject.send("Hello?? :(")

输出：

New subscription!
Received new value!
Subscriber received value: Hello!
Received new value!
Subscriber received value: Hello again!
Received new value!
Subscriber received value: Hello for the last time!
A subscription completed
Subscriber received value: Failure

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