How to send data from one component to another using a shared service [duplicate]

Question

I wanted to send data using subject to another component (for a earning purpose). I am not able to fetch back the data. Here is my code:

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);
  }

}

I am not getting the value in console.

Here is the working Demo : DEMO

Answer 1

By putting:

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

in both components, you are creating two distinct instances of the shared service. Each instance is not 'aware' of the data from each component. Provide it at module level and create a singleton service:

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

This way, you inject the service as a single instance in the both components, so they can share it as they will share the data.

Or using the Angular's preferred new way :

Beginning with Angular 6.0, the preferred way to create a singleton service is to specify on the service that it should be provided in the application root. This is done by setting providedIn to root on the service's @Injectable decorator:

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

Demo

See also