Angular6 如何在路由组件中检测AppComponent的更改？

无论什么时候我要对货币代码进行更改，它在 AppComponent它也应该反映在CurrencyExchangeComponent中

export class AppComponent implements OnInit {
      currencyCode: string = 'INR';

      changeCurrency(currencyCode:string){
        this.currencyCode = currencyCode; }
    }


export class CurrencyExchangeComponent{
       fromCurrency:string = 'INR';
       toCurrency:string = 'INR';

     exchangeCurrency(){
       //service call
     }
}