How can I access the main component's functions from a page navigated to in Ionic 2?

Question

I've created an Ionic v2 application using the following command:

ionic start my-app sidemenu --v2 --ts.

Inside the app.ts file, I have some logic (functions) to do some things (like opening a modal and maintaining state for what the side menu should show). When a certain page (e.g. pages/getting-started/getting-started.ts) is shown, I'd like to reuse the same functions in app.ts. How do I access functions of app.ts from a page navigated to?

My app.ts looks like the following.

class MyApp {
 @ViewChild(Nav) nav:Nav;
 private rootPage:any = GettingStartedPage;
 private pages:any;

 constructor(platform:Platform) {
  this.initializeApp();
  this.pages = { 
   'GettingStartedPage': GettingStartedPage, 
   'AnotherPage': AnotherPage //more pages and modals
  };
 }

 initializeApp() {
  this.platform.ready().then(() => {
   StatusBar.styleDefault();
  });
 }

 openPage(page:string) {
  //when a user clicks on the left menu items, a new page is navigated to
  let component this.pages[page];
  this.nav.setRoot(component);
 }

 openModal(page:string) {
  //modals are opened here, there's more complicated logic
  //but this serves to demonstrate my problem
  let component = this.pages[page];
  Modal.create(component);
 }
}

ionicBootstrap(MyApp);

My getting-started.ts looks like the following.

export class GettingStartedPage {
 constructor(
  platform:Platform, 
  viewController:ViewController,
  navController:NavController,
  navParams:NavParams) {
 }

 buttonClicked() {
  //i need to access app.ts openModal here
  //how do i call a method on app.ts?
  //like MyApp.openModal('SomeModal');
 }
}

Answer 1

With a shared service, you can communicate across the whole application.

Create a service class like

@Injectable() 
class SharedService {
  // use any kind of observable to actively notify about new messages
  someEvent:Subject = new Subject(); 
}

Provide it on your app

@App({
  ...
  providers: [SharedService]
})

Inject it to the App component and any component, directive, or service you want to communicate to the App component from

constructor(private sharedService:SharedService) {}

someEventHandler() {
  this.sharedService.someEvent.next('some new value');
}

In the App component subscribe to notifications

constructor(sharedService:SharedService) {
  sharedService.someEvent.subscribe(event => {
    if(event == ...) {
      this.doSomething();
    }
  });
}

For details see https://angular.io/docs/ts/latest/cookbook/component-communication.html