ionic 2 page change event

Question

I want to execute some code every time the page changes.

I could add add an ngOnDestroy method to every page. It appears that I could use Ionic 2 page lifec

Answer 1

As of Ionic 3.6, you can use the App component to subscribe to application-wide page change events, as documented in : https://ionicframework.com/docs/api/components/app/App/

For example, if you'd like to track every view change in Google Analytics using the GA cordova plugin, you could amend your app.component.ts like this :

constructor(private app: App, private platform: Platform, private ga: GoogleAnalytics, ...) {
  this.platform.ready().then(() => {
    this.ga.startTrackerWithId('UA-XXX').then(() => {
      this.app.viewDidEnter.subscribe((evt) => {
        // evt.instance is the Ionic page component
        this.ga.trackView(evt.instance.title);
      });
    }).catch(e => console.log('Doh', e));
  }
}

Answer 2

In Ionic2+ you can simply subscribe to the event you want to execute your code on as follows:

this.navCtrl.ionViewWillUnload.subscribe(view => {
    console.log(view);
});

You can subscribe to all the Lifecycle Events

Answer 3

You can use plain old Javascript to be placed in app.component.ts. Assuming that you use Ionic2-RC0:

import { Component } from '@angular/core';
import { Platform } from 'ionic-angular';
import { StatusBar } from 'ionic-native';

import { YourPage } from '../pages/yourpage/yourpage';

@Component({
  template: `<ion-nav [root]="rootPage"></ion-nav>`
})
export class MyApp {
  rootPage = YourPage;

  constructor(platform: Platform) {
    platform.ready().then(() => {

      // Okay, so the platform is ready and our plugins are available.
      // Here you can do any higher level native things you might need.
      StatusBar.styleDefault();
      window.addEventListener('load', () =>{
         console.log('page changed');
      });
    });
  }

Every time you change page using the NavController, you'll have page changed printed out in the console.

Answer 4

Ionic2 doesn't use Angular2's Router. They have their own implementation NavController.

---

I see that you can subscribe to Angular 2 Router events. How do I translate that for use in Ionic 2?

You can merge all the NavController Events and subscribe to it.

allEvents = Observable.merge(
                 this.navController.viewDidLoad, 
                 this.navController.viewWillEnter, 
                 this.navController.viewDidEnter, 
                 this.navController.viewWillLeave, 
                 this.navController.viewDidLeave, 
                 this.navController.viewWillUnload);

allEvents.subscribe((e) => {
    console.log(e);
});

Answer 5

Another option would be to create a super class where you can use the ionViewDidUnload method (or any other lifecycle hook) like this:

import { Events } from 'ionic-angular';

export class BasePage {

  constructor(public eventsCtrl: Events) { }

  ionViewDidEnter() {
    this.eventsCtrl.publish('page:load');   
  }

  ionViewDidUnload() {
    this.eventsCtrl.publish('page:unload');   
  }
}

Then in every page you just need to extend that BasePage

@Component({
  templateUrl: 'build/pages/my-page/my-page.html',
})
export class MyPage extends BasePage {

constructor(private platform: Platform,
              private nav: NavController, 
              private menuCtrl: MenuController,
              ...,
              eventsCtrl: Events) //notice that this one does not have the private/public keyword 
  {    

    // Due to an issue in angular, by now you must send the dependency to the super class
    // https://github.com/angular/angular/issues/5155
    super(eventsCtrl);

    //...
}

And then, you can add a method like this one in the main app.ts file to respond to those events:

  private initializeEventHandlers() {

    this.events.subscribe('page:load', () => {
      // your code...
    });

    this.events.subscribe('page:unload', () => {
      // your code...
    });

  }

Answer 6

1st thing Router is present in @angular/router module.

And for listening route change event you can place subscription on router changes object.

Code

class MyRouteEventClass {
  constructor(private router: Router) {
     router.changes.subscribe((val) => {
       /* Awesome code here */
     }
    )
  }
}