Subject和BehaviorSubject有什么区别？

我不清楚a Subject和a 之间的区别BehaviorSubject。只是BehaviorSubject具有getValue()功能吗？

一个BehaviorSubject拥有一个值。订阅后，它将立即发出该值。主题没有值。

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示例：

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

控制台输出：1

此外：

• BehaviorSubject 可以使用初始值创建：新 Rx.BehaviorSubject(1)
• 考虑ReplaySubject是否要让主体保留一个以上的值

行为主体

BehaviourSubject将在订阅上返回初始值或当前值

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

学科

主题不返回“订阅”上的当前值。它仅在.next(value)调用时触发并返回/输出value

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);

在控制台上显示以下输出：

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

我刚刚创建了一个项目，解释了所有主题之间的区别：https :
//github.com/piecioshka/rxjs-subject-vs-behavior-vs-replay-vs-async

它可能会帮助您理解。

import * as Rx from 'rxjs';

const subject1 = new Rx.Subject();
subject1.next(1);
subject1.subscribe(x => console.log(x)); // will print nothing -> because we subscribed after the emission and it does not hold the value.

const subject2 = new Rx.Subject();
subject2.subscribe(x => console.log(x)); // print 1 -> because the emission happend after the subscription.
subject2.next(1);

const behavSubject1 = new Rx.BehaviorSubject(1);
behavSubject1.next(2);
behavSubject1.subscribe(x => console.log(x)); // print 2 -> because it holds the value.

const behavSubject2 = new Rx.BehaviorSubject(1);
behavSubject2.subscribe(x => console.log('val:', x)); // print 1 -> default value
behavSubject2.next(2) // just because of next emission will print 2 

BehaviorSubject将可观察对象发出的最后一个值保留在内存中。一个普通的Subject没有。

BehaviorSubject就像ReplaySubject缓冲区大小为1。