Swift  之 RxSwift(1)

RxSwift

官方文档结构

1. Introduction:
2. Subjects
3. Transforming Observables
4. Filtering Observables
5. Combining Observables
6. Error Handing Operators
7. Observable Utility Operators
8. Conditional and Boolean Operators
9. Mathematical and Aggregate Operators
10. Connectable Observable Operatiors

Observable

Observable 是观察者模式中被观察的对象，相当于一个事件序列(GeneratorType)， 会向订阅者发送新产生的事件信息。

事件信息分为：

.Next(value): 表示新的事件数据
.Completed: 表示事件序列完结
.Error: 异常导致的事件序列完结

Subjects

A Subject is a sort of bridge or proxy that is available in some implementations of ReactiveX that acts both as an observer and as an Observable.

Subject可以看做是一种代理和桥梁。它既是订阅者又是订阅源，这意味着它既可以订阅其他Observables，同时又可以对他的订阅者发送事件

1. How To Create Observables ?

1. empty:

   empty creates an empty sequence.
   The only message it sends is the .Completed message.
   
   let emptySequence = Observable<Int>.empty()

2. never:

   never creates a sequence that never sends any element or completes.
   
   let neverSequence = Observable<Int>.never()

3. just (一个元素)

   just represents sequence that contains one element.
   It sends two messages to subscribers.
   The first message is the value of single element and the second
   message is .Completed.
   
   let singleElementSequence = Observable.just(32)

4. sequenceOf (一系列元素)

   sequenceOf creates a sequence of a fixed number of elements.

5. from (将swift的序列(SequenceType) 转换为事件序列)

   from creates a sequence from SequenceType
   
   let sequenceFromArray = [1, 2, 3, 4, 5].toObservable()

6. create (通过闭包创建序列)

   create creates sequence using Swift closure.
   This examples creates custom version of just operator.
   
   let myJust = { (singleElement: Int) -> Observable<Int> in
       return Observable.create { observer in
       observer.on(.Next(singleElement))
       observer.on(.Completed)
   
       return NopDisposable.instance
       }
   }
   
   let subscription = myJust(5)
       .subscribe { event in
           print(event)
   }

7. generate

   generate creates sequence that generates its values and determines
   when to terminate based on its previous values.
   
   let generated = Observable.generate(
       initialState: 0,
       condition: { $0 < 3 },
       iterate: { $0 + 1 }
   )
   
   let subscription = generated
      .subscribe { event in
       print(event)
   }

8. failWith

   create an Observable that emits no items and terminates with an error
   
   let error = NSError(domain: "Test", code: -1, userInfo: nil)
   let erroredSequence = Observable<Int>.error(error)

9. deferred (加载延迟， 订阅者的内容相同而完全独立)

   do not create the Observable until the observer subscribes,
   and create a fresh Observable for each observer

2. How To Create Subjects

1. PublishSubject（发送订阅者从订阅之后的事件序列）

   PublishSubject emits(发出) to an observer only those items that
   are emitted by the source Observable(s) subsequent to the
   time of the subscription.
   
   example("PublishSubject") {
       let disposeBag = DisposeBag()
   
       let subject = PublishSubject<String>()
       writeSequenceToConsole("1", sequence: subject).addDisposableTo(disposeBag)
       subject.on(.Next("a"))
       subject.on(.Next("b"))
       writeSequenceToConsole("2", sequence: subject).addDisposableTo(disposeBag)
       subject.on(.Next("c"))
       subject.on(.Next("d"))
   }
   1 - a
   1 -  b
   1 - c
   2 - c
   1 - d
   2 - d

2. ReplaySubject (在新订阅对象订阅的时候会补发所有已经发送过的数据列， buffize: 是缓冲区的大小， 为1时，那么新订阅者出现的时候就补发上一个事件，如果是2， 就补发2个 ，…)

   ReplaySubject emits to any observer all of the items that
   were emitted by the source Observable(s), regardless of
   when the observer subscribes.
   
   example("ReplaySubject") {
       let disposeBag = DisposeBag()
       let subject = ReplaySubject<String>.create(bufferSize: 1)
   
       writeSequenceToConsole("1", sequence: subject).addDisposableTo(disposeBag)
       subject.on(.Next("a"))
       subject.on(.Next("b"))
       writeSequenceToConsole("2", sequence: subject).addDisposableTo(disposeBag)
       subject.on(.Next("c"))
       subject.on(.Next("d"))
   }
   print:
   1 - a
   1 - b
   2 - b // 补发1个
   1 - c
   2 - c
   1 - d
   2 - d 

3. BehaviorSubject (在新的订阅对象订阅的时候回发送最近发送的事件，如果没有，则发送一个默认值)

   When an observer subscribes to a BehaviorSubject, it begins
   by emitting the item most recently emitted by the source
   Observable (or a seed/default value if none has yet been emitted)
   and then continues to emit any other items emitted later
   by the source Observable(s).
   
   example("BehaviorSubject") {
       let disposeBag = DisposeBag()
   
       let subject = BehaviorSubject(value: "z")
       writeSequenceToConsole("1", sequence: subject).addDisposableTo(disposeBag)
       subject.on(.Next("a"))
       subject.on(.Next("b"))
       writeSequenceToConsole("2", sequence: subject).addDisposableTo(disposeBag)
       subject.on(.Next("c"))
       subject.on(.Next("d"))
       subject.on(.Completed)
   }
   print:
   1 - z
   1 - a
   1 - b
   2 - b
   1 - c
   2 - c
   1 - d
   2 - d
   1 - com
   2 - com

4. Variable (是基于BehaviorSubject的一层封装， 它的优势： 不会被显示的终结，即：不会受到.Complete或者.Error这类终结事件，它会主动在析构的时候发送.Complete)

   Variable wraps BehaviorSubject. Advantage of using variable over
   BehaviorSubject is that variable can never explicitly complete
   or error out, and BehaviorSubject can in case Error or Completed
   message is send to it. Variable will also automatically complete
   in case it‘s being deallocated.
   
   example("Variable") {
       let disposeBag = DisposeBag()
       let variable = Variable("z")
       writeSequenceToConsole("1", sequence: variable.asObservable()).addDisposableTo(disposeBag)
       variable.value = "a"
       variable.value = "b"
       writeSequenceToConsole("2", sequence: variable.asObservable()).addDisposableTo(disposeBag)
       variable.value = "c"
       variable.value = "d"
   }

3. Transforming Observables

1. map/select

More info in reactive.io website

example("map") {
    let originalSequence = Observable.of(1, 2, 3)

    _ = originalSequence
        .map { number in
            number * 2
        }
        .subscribe { print($0) }
}