Observing controller property (participating in queryparam) from service without observer - ember.js

Question

I moved state properties from controller to service except queryParams. now I would like to have one of the query param property to service.
Is there any way to achieve this without using observer ?.
I am currently doing it using observer.
controllers/application.js
import Ember from 'ember';
const {computed,observer} = Ember;
export default Ember.Controller.extend({
myService:Ember.inject.service(),
appName: 'Ember Twiddle',
changedAppName:observer('appName',function(){
this.get('myService').changeAppName(this.get('appName'));
}),
actions:{
changeApp(){
this.set('appName','NewEmberApp');
}
}
});
templates/application.hbs
<h1>Welcome to {{myService.appName}}</h1>
<br>
<button {{action "changeApp"}}>Change</button>
<br>
{{outlet}}
<br>
<br>
services/my-service.js
import Ember from 'ember';
export default Ember.Service.extend({
appName:'SSS',
changeAppName(param){
this.set('appName',param);
}
});
EmberTwiddle

Answer 1

Why do you need the observer at all? Just set the appName of the service directly inside your changeApp action of the controller: this.set('myService.appName','Kumkanillam');
and remove the observer completely.
Your question became sth. different after your comment. Let me clarify if I understand your question correctly with the following twiddle. In that case; you are modifying appName both at controller and component; which is an illustration of violation of DDAU principle. In this situation you need observer inside the controller in order to be notified about appName change at component level.
In order to solve this problem; you can create an aliased computed property at controller level and pass it to component (or other components or route templates) and you will get rid of the observer. This twiddle explains what I mean.
Even if what I understood is correct and what I provided might be a valid answer; do not forget that violating DDAU will hurt you at some point and you are going to have to refactor your code in future. Hope this helps.