BehaviourSubject

behavionsubject将返回订阅上的初始值或当前值

var bSubject= new Rx.BehaviorSubject(0);  // 0 is the initial value

bSubject.subscribe({
  next: (v) => console.log('observerA: ' + v)  // output initial value, then new values on `next` triggers
});

bSubject.next(1);  // output new value 1 for 'observer A'
bSubject.next(2);  // output new value 2 for 'observer A', current value 2 for 'Observer B' on subscription

bSubject.subscribe({
  next: (v) => console.log('observerB: ' + v)  // output current value 2, then new values on `next` triggers
});

bSubject.next(3);

输出:

observerA: 0
observerA: 1
observerA: 2
observerB: 2
observerA: 3
observerB: 3

主题

主题没有返回订阅上的当前值。它只触发.next(value)调用并返回/输出该值

var subject = new Rx.Subject();

subject.next(1); //Subjects will not output this value

subject.subscribe({
  next: (v) => console.log('observerA: ' + v)
});
subject.subscribe({
  next: (v) => console.log('observerB: ' + v)
});

subject.next(2);
subject.next(3);

在控制台上输出如下信息:

observerA: 2
observerB: 2
observerA: 3
observerB: 3

这三个都很不同，让我再举几个例子，

const subject = new Rx.Subject();
const behaviorSubject = new Rx.BehaviorSubject([]);
const relaySubject = new Rx.ReplaySubject();


subject.next(1)

behaviorSubject.next(1); 
behaviorSubject.next(2); 
behaviorSubject.next(3);

relaySubject.next(1); 
relaySubject.next(2); 
relaySubject.next(3);

subject.subscribe(val => console.log('From Subject', val)); // this will not emits
behaviorSubject.subscribe(val => console.log('From BehaviorSubject', val)); // this will emits only last value
relaySubject.subscribe(val => console.log('From ReplaySubject', val)); // this will emit all values

输出截图

正如你所看到的，当我们在发出(i。e(…)),

主题-这将不会被发射 behaviorSubject -这将使用最后一个值触发一次 ReplaySubject -这将发射3次，因为我们有很多next()

所以区别主要在于订阅的位置，是在next()之前还是在next()之后。

在实际情况下，我们只在next() [i。E在我们向受试者填写数据后]。

一个BehaviorSubject包含一个值。当它被订阅时，它立即发出该值。Subject不包含值。

主题示例(使用RxJS 5 API):

const subject = new Rx.Subject();
subject.next(1);
subject.subscribe(x => console.log(x));

控制台输出将为空

BehaviorSubject例子:

const subject = new Rx.BehaviorSubject(0);
subject.next(1);
subject.subscribe(x => console.log(x));

控制台输出:1

此外:

BehaviorSubject应该创建一个初始值: 如果您希望主题获得以前发布的值，请考虑ReplaySubject。

一个行为主体在订阅后发出一个值，一个Subject no。

// Subject
const mySubject = new Rx.Subject().subscribe((v) => console.log(v)); // will return nothing

// BehaviorSubject
const myBehaviorSubject = new Rx.BehaviorSubject(666).subscribe((v) => console.log(v)); // will return 666 when subscription occurs

我刚刚创建了一个项目来解释所有科目之间的区别: https://github.com/piecioshka/rxjs-subject-vs-behavior-vs-replay-vs-async

程序测试所有4个主题类型: 主题，行为主题，重玩主题和AsyncSubject

// 1. Subject - only value after subscribed
var subject = new Subject();
subject.next(1);
subject.next(2);
subject.complete();
subject.subscribe(
  (data) => this.log("Subject="+data),
  (error) => this.log(error),
  () => this.log('Complete Subject')
);
subject.next(3);
subject.next(4);

// 2. BehaviorSubject - only last value before subscribed and all after subscription
// calls on initalization, mandatory to specify a value
var subjectb = new BehaviorSubject<any>(5);
subjectb.next(1);
subjectb.next(2);
subjectb.complete();
subjectb.subscribe(
  (data) => this.log("Behavior="+data),
  (error) => this.log(error),
  () => this.log('Complete Behavior')
);

// 3. ReplaySubject - all specified last values before subscribed and all after subscription
// Does not call on initalization, no default value
var subjectr = new ReplaySubject(5);
subjectr.next(1);
subjectr.next(2);
subjectr.complete();
subjectr.subscribe(
  (data) => this.log("Replay="+data),
  (error) => this.log(error),
  () => this.log('Complete Replay')
);

// 4. AsyncSubject - only last values before calling complete
var subjecta = new AsyncSubject();
subjecta.next(1);
subjecta.next(2);
subjecta.complete();
subjecta.subscribe(
  (data) => this.log("Async="+data),
  (error) => this.log(error),
  () => this.log('Complete Async')
);

https://stackblitz.com/edit/example-rxjs-subject-e8vj9y?embed=1&file=app/app.component.ts