How to update Data in 2 components using single in

Question

This is my service class in which i have one variable called " dataValue".

import { Injectable } from '@angular/core';
@Injectable()
export class DataService 
{
 constructor() 
{
console.log("new instance");
  }
 dataValue: string = "initial value";
}

Here it is my first component in which i am getting and intializing the service variable with the variable i define in this component.and implementing two way data binding on component variable.

import { Component } from '@angular/core';
import { DataService } from './dataservice';

@Component({
selector: 'first',

 template: `
                 <div>
                        Your Input : <input type = "text" [(ngModel)] = "ChangeByFirstComponent">
                        You Entered : {{ChangeByFirstComponent}}
                 </div>   
                `
})
export class FirstComponent {
constructor(private _dataService: DataService) { }

ChangeByFirstComponent: string;

get DataValue(): string {
return this._dataService.dataValue;
 }

 set DataValue(ChangeByFirstComponent){
 {
  this._dataService.dataValue = this.ChangeByFirstComponent;
  }
}

and here it is my second component , doing the same thing here just as firstcomonent

import { Component } from '@angular/core';
import { DataService } from './dataservice';

@Component({
    selector: 'second',
    template: `
                 <div>
                        Your Input : <input type = "text" [(ngModel)] = "ChangeBySecondComponent">
                        You Entered : {{ChangeBySecondComponent}}
                 </div>  ` 

})

export class SecondComponent {
    constructor(private _dataService: DataService) { }
    ChangeBySecondComponent: string;

    get DataValue(): string {
        return this._dataService.dataValue;
    }

    set DataValue(ChangeByFirstComponent) {
        this._dataService.dataValue = this.ChangeBySecondComponent;
    }
}

i want the functionality like if the user input something from first component, the second component will get the change too rapidly due to single instance of the service class

Answer 1

You can achieve this type of functionality by using BehaviorSubject. When there is a change in first component you can push that change to BehaviorSubject and then subscribe to that in second component, so it gets the changes as they appear in first component. You can do something like this,

import { Injectable } from '@angular/core';
@Injectable()
export class DataService 
{
 dataSubject: BehaviorSubject;
 constructor() 
{
this.dataSubject = new BehaviorSubject(null);
console.log("new instance");
  }
pushChanges(dataValue) {
  this.dataSubject.next(dataValue);
}
getChanges() {
  return this.dataSubject.asObservable();
}
 dataValue: string = "initial value";
}

In your first component, you can write,

this._dataService.pushChanges(this.ChangeByFirstComponent); 

And in your second component,

this._dataService.getChanges().subscribe( 
changeByFirstComponent => {   

  // this method will be triggered only when there is change in first component 
  // and it's pushed on the `dataSubject`

  console.log(changeByFirstComponent);
}
)

You can repeat this process, you want the reverse functionality too.