主题和行为主题有什么区别？

Question

我不清楚 Subject 和 BehaviorSubject 之间的区别。仅仅是 BehaviorSubject 有 getValue() 功能吗？

原文由 Mike Jerred 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

一个 BehaviorSubject 拥有一个值。当它被订阅时，它会立即发出值。主题不包含值。

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

行为主体示例：

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

控制台输出：1

此外：

• BehaviorSubject 应该使用初始值创建：新的 Rx.BehaviorSubject(1)
• 如果您希望主题获得以前发布的值，请考虑 ReplaySubject 。

原文由 ZahiC 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 2

测试所有 4 种主题类型的程序： 主题、行为主题、重播主题和异步主题

// 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

原文由 Sameer Jadhav 发布，翻译遵循 CC BY-SA 4.0 许可协议