Tips for transferring information between different components through a collaborative service

Attempting to send data using a subject to another component for the purpose of earning, but experiencing difficulty retrieving the data. Below is the provided code snippet:

app.component.ts

import { Component } from '@angular/core';
import { shareService } from './share.service';

@Component({
 selector: 'my-app',
  template: `
  <hello></hello>
  <button (click)="passData()">
    Start
  </button>
  `,
  styleUrls: [ './app.component.css' ],
  providers:[shareService]
})
export class AppComponent  {
  constructor(private service : shareService){}

  passData(){
   this.service.send("hello");
}

}

hello.component.ts

import { Component, Input } from '@angular/core';
import { shareService } from './share.service';
import { Subscription }   from 'rxjs/Subscription';

@Component({
  selector: 'hello',
  template: `<h1>Hello!</h1>`,
  styles: [`h1 { font-family: Lato; }`],
  providers:[shareService]
})
export class HelloComponent  {
  subscription: Subscription;
    constructor(private share : shareService){
    this.subscription =  share.subj$.subscribe(val=>{
    console.log(val);
    })
  }
}

share.service.ts

import { Injectable } from '@angular/core';
import { Subject }    from 'rxjs/Subject';

@Injectable()
export class shareService{

  private sub = new Subject();
  subj$ = this.sub.asObservable();

    send(value: string) {
    this.sub.next(value);
  }

}

Issue with receiving the value in the console remains unresolved.

For a live demonstration, please visit the following link: DEMO

Answer №1

When you include the shared service in both components like this:

@Component({
  .....
  providers: [sharedService]
})

You are actually creating two separate instances of the shared service. Each instance does not have access to data from the other component. To solve this issue, consider providing the service at the module level to create a singleton service:

@NgModule({
  ....
  providers: [sharedService]
})

This approach allows you to inject the service as a single instance into both components, enabling them to share data effectively.

Alternatively, you can follow Angular's recommended method:

Starting with Angular 6.0, it is best practice to designate a service as a singleton by specifying providedIn root in the @Injectable decorator of the service:

@Injectable({
  providedIn: 'root',
})

Check out this demo for more information.

For additional insights on this topic, refer to this post.

Answer №2

Using sub$ may seem unnecessary, but it is not required in this case

// Data is simply pushed to the subject. BehavourSubject can be used to initialize a value.
@Injectable()
export class shareService{

  private sub = new Subject();

    confirmMission(astronaut: string) {
    this.sub.next(astronaut);
  }

}

In your second component, subscribe to it like so:

@Component({
  selector: 'hello',
  template: `<h1>Hello!</h1>`,
  styles: [`h1 { font-family: Lato; }`],
  providers:[shareService]  // This can be declared at module level or component level
})
export class HelloComponent  {
  subscription: Subscription;
    constructor(private share : shareService){
    this.subscription =  share.subj.subscribe(val=>{
    console.log(val);
    })
  }
} 

Remember to provide your service at the module level or include it in both components.

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