[Swift 开发] Combine使用方法
这片主要介绍Combine基本用法
1. Just
let myPublisher = Just("1")
let myScriber = Subscribers.Sink<String, Never> { completion in
if completion == .finished {
print("myScriber1 Finished")
} else {
print("myScriber1 Failure")
}
} receiveValue: { value in
print(value)
}
myPublisher.subscribe(myScriber)
打印结果：
// 1
// myScriber1 Finished1. Just发布一个Publisher，just只会发送一次，发送完成结束本次订阅
2. Sink订阅者，订阅了Just，这个Sink后面是个泛型
第一参数是参数类型，方法Just发送的是String类型，所以咱们观察者类型要保持一致
第二参数是错误类型，例子中参数是Never,就是不会报错，下面的例子中会介绍其它的
3. Sink中有两个闭包 (receiveCompletion和receiveValue)
receiveCompletion: 结束观察订阅
receiveValue: 订阅结果
extension Publisher {
public func sink(receiveCompletion: @escaping ((Subscribers.Completion<Self.Failure>) -> Void), receiveValue: @escaping ((Self.Output) -> Void)) -> AnyCancellable
}
extension Publisher where Self.Failure == Never {
public func sink(receiveValue: @escaping ((Self.Output) -> Void)) -> AnyCancellable
}
// 如果不需要receiveCompletion，我们可以用Self.Failure == Never方法2. Publishers
Publishers处于pipline的最上游，它的主要作用是发送数据
let arr = 0...3
arr.publisher.sink { value in
print(value)
}
打印结果：
// 0
// 1
// 2
// 3Combine给了我们一个简便的写法
适用环境，比如我们在意的是直接拿到结果，不需要中间的Operator
3. assign
class Person {
var age: Int = 0 {
didSet {
print("age: \(age)")
}
}
}
let person = Person()
let range = 0...2
range.publisher.assign(to: \.age, on: person)
打印结果：
// 0
// 1
// 2keyPath
将发布者中的每个元素分配给对象上的属性。
使用Publisher/assign(to:on:)订阅者，当你想在每次发行者产生一个值时设置给定的属性。
在这个例子中，Publisher/assign(to:on:) 在person的实例上设置age属性的值
第二种用法
class Person {
@Published var age: Int = 0
}
let person = Person()
Just(1).assign(to: &person.$age)
print(person.age)
打印结果：
// 1熟悉SwiftUI的朋友看起来比较喜欢，属性包装器的写法
** assign 都是 Self.Failure == Never
4. Future
class Person {
var age: Int = 0
}
let futurePubliser = Future<Int ,Never> { promise in
print("异步操作")
promise(.success(2))
}
let subscribers = Subscribers.Sink<Int,Never> { completion in
if completion == .finished {
print("Finished")
} else {
print("Failure")
}
} receiveValue: { value in
print(value)
}
futurePubliser.subscribe(subscribers)
let person = Person()
futurePubliser.assign(to: \.age, on: person)
打印结果：
// 异步操作
// 2
// FinishedFuture和Just类似，区别在于：
Just直接发送参数, Failure = Never
Futrre是调用一个异步闭包，可以选择闭包结束时发送数据, Failure = Error
5. Operator
let myPubliser2 = Just("1")
let tansValue = Publishers.Map<Just<String>, Int>(upstream: myPubliser2) { value in
return Int(value) ?? 0
}
let myScriber2 = Subscribers.Sink<Int,Never> { completion in
if completion == .finished {
print("Finished")
} else {
print("Failure")
}
} receiveValue: { value in
print(value)
}
tansValue.subscribe(myScriber2)
打印结果：
// 1
// Finished使用提供的闭包转换来自上游发布者的所有元素的发布者
Operator处于pipline的中游，它的主要作用是接收数据，处理数据，再发送数据
此发布者可能发布的错误类型, 此发布者使用其上游发布者的失败类型。
6. Operator2
_ = Just(1).filter({ value in
return value < 10
}).sink(receiveCompletion: { completion in
if completion == .finished {
print("Finished")
} else {
print("Failure")
}
}, receiveValue: { value in
print(value)
})
打印结果：
// 1
// Finishedextension Just {
public func filter(_ isIncluded: (Output) -> Bool) -> Optional<Output>.Publisher
}
注意这个filter，它不是高阶函数里的那个filter，虽然它们功能都是数据过滤。但它属于Just, 它返回的是Publisher
7. CurrentValueSubject send
// 定义一个错误类型
enum myErrors: Error {
case wrongValue
}
// 定义一个publiser
let publiser = CurrentValueSubject<String, myErrors>("10")
// 第一个接收者
publiser.filter {
return $0.count < 2
}.sink { completion in
if completion == .failure(myErrors.wrongValue) {
print("Scriber1 Finished")
} else {
print("Scriber1: \(completion)")
}
} receiveValue: { value in
print("Scriber1: \(value)")
}
// 第二个接收者
let myScriber = Subscribers.Sink<String,myErrors> { completion in
if completion == .failure(myErrors.wrongValue) {
print("Scriber2 Finished")
} else {
print("Scriber2: \(completion)")
}
} receiveValue: { value in
print("Scriber2: \(value)")
}
publiser.subscribe(myScriber)
// 开始发送数据
publiser.send("1")
publiser.send("11")
publiser.send(completion: .failure(.wrongValue))
publiser.send("over")
打印结果：
// Scriber2: 10
// Scriber1: 1
// Scriber2: 1
// Scriber2: 11
// Scriber1 Finished
// Scriber2 FinishedCurrentValueSubject可以订阅一个publiser, 它可以多点用send发布数据，直到发送completion结束观察
Failure = Error
8. CurrentValueSubject Operator
let subject1: CurrentValueSubject<Int,myErrors> = .init(10)
let subject2: CurrentValueSubject<Int,myErrors> = .init(20)
// 数据流 subject1 -> subject2
_ = subject1.subscribe(subject2)
let myScriber = Subscribers.Sink<Int,myErrors> { completion in
if completion == .finished {
print("Finished")
} else {
print("Failure")
}
} receiveValue: { value in
print(value)
}
subject2.receive(subscriber: myScriber)
subject1.send(1)
subject1.send(2)
subject2.send(3)
subject1.send(completion: .failure(.wrongValue))
subject1.send(11)
subject2.send(12)
打印结果：
// 10
// 1
// 2
// 3
// FailureCurrentValueSubject也可以当作Operator适用
例子中subject1处于pipline的上游，subject2处于pipline的中游
Failure = Error
subject1.send(1) // subject1 -> subject2 ->Scriber
subject1.send(2) // subject1 -> subject2 ->Scriber
subject2.send(3) // subject2 ->Scriber
subject1.send(completion: .failure(.wrongValue)) // 结束myScriber的响应者
9. PassthroughSubject
let subject1: PassthroughSubject<Int,myErrors> = PassthroughSubject()
let subject2: PassthroughSubject<Int,myErrors> = PassthroughSubject()
// 数据流 subject1 -> subject2
let cancelable = subject1.subscribe(subject2)
let myScriber = Subscribers.Sink<Int,myErrors> { completion in
if completion == .finished {
print("Finished")
} else {
print("Failure")
}
} receiveValue: { value in
print(value)
}
subject2.receive(subscriber: myScriber)
subject1.send(1)
subject1.send(2)
subject2.send(3)
subject1.send(completion: .failure(.wrongValue))
subject1.send(11)
subject2.send(12)
打印结果：
// 1
// 2
// 3
// FailurePassthroughSubject和CurrentValueSubject功能类似
区别在于
CurrentValueSubject： 有个初始化值
PassthroughSubject：没有初始化值