我不清楚主体和行为主体之间的区别。仅仅是因为一个行为主体有getValue()函数吗?
当前回答
这可能会帮助你理解。
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
其他回答
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。
BehaviorSubject在内存中保存被观察对象发出的最后一个值。一个普通的实验对象没有。
BehaviorSubject类似于缓冲区大小为1的ReplaySubject。
更新:有边缘用例可以区分这两者。https://medium.com/javascript-everyday/behaviorsubject-vs-replaysubject-1-beware-of-edge-cases-b361153d9ccf
TLDR: 如果您想在订阅时提供一个初始值,即使到目前为止还没有将任何内容推送到Subject,也可以使用BehaviorSubject。如果你想让观察者重放最后一个值,即使一个Subject已经关闭,也可以使用ReplaySubject(1)。
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
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
这可能会帮助你理解。
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
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