Angular 4 Rxjs 主题订阅不起作用

Question

I have a shared service data.service.ts which have

public pauseProjectTask$: Subject<any> = new Subject<any>();

pauseTaskProject(taskData,type){
    this.pauseProjectTask$.next(taskData);             
}

and I have a footer.component.ts which shows currently active task in each pages, task can be paused from footer component. I have a pause function in footer.

pauseTask(taskData,type){
    console.log(taskData,type);
    this.pauseTaskSub = this.dataService.pauseTaskProject(taskData,type);
}

and I have other component which lists all tasks. task.component.ts . it listens for task status change.

this.pauseProjectTaskSub = this.dataService.pauseProjectTask$.subscribe(taskData => {
      this.changesTaskStatus('','pause',taskData);
});


ngOnDestroy(){
    this.pauseProjectTaskSub.unsubscribe();        
}

its unsubscribed OnDestroy .

when I call pauseTaskProject() which is in footer component it calls pauseTaskProject() in data.service.ts

pauseTaskProject is called but it didn't subscribe in tasks.component.ts

1. Task is started from tasks page, which is tasks.component.ts
2. Switch to other page and pause task from footer component. It doesn't work
3. It works when I don't use unsubscribe. but if unsubscribe is not used, subscribe calls multiple time.

Answer 1

Give the lack of information, most probably the subscription is triggered after the function this.dataService.pauseTaskProject(taskData,type) is called. Subscriptions to Subject observable emit notifications that are pushed to it only after the subscription.

If you need the previously pushed value to the observable, you could either use BehaviorSubject or ReplaySubject . I'll illustrate with ReplaySubject with buffer size 1. It'll hold/buffer the previously pushed value to it and emit it immediately upon subscription.

import { ReplaySubject } from 'rxjs';

public pauseProjectTask$: ReplaySubject<any> = new ReplaySubject<any>(1);
...