How to handle back button on Ionic 2

How can I handle the back button action on Ionic 2?

I want to be able to know what to do depending on which page is being shown to the user.

I didn't find a good answer to this question, but after a while I figured it out myself a way to do it. I'm gonna share with you all.

Thanks

Here's how I did it:

In every Page component, I created a function called backButtonAction(), which will execute custom code for every page.

Code:

import { Component } from '@angular/core';
import { Platform, NavController, ModalController } from 'ionic-angular';
import { DetailsModal } from './details';

@Component({
    selector: 'page-appointments',
    templateUrl: 'appointments.html'
})
export class AppointmentsPage {
    modal: any;

    constructor(private modalCtrl: ModalController, public navCtrl: NavController, public platform: Platform) {
        // initialize your page here
    }

    backButtonAction(){
        /* checks if modal is open */
        if(this.modal && this.modal.index === 0) {
            /* closes modal */
            this.modal.dismiss();
        } else {
            /* exits the app, since this is the main/first tab */
            this.platform.exitApp();
            // this.navCtrl.setRoot(AnotherPage);  <-- if you wanted to go to another page
        }
    }

    openDetails(appointment){
        this.modal = this.modalCtrl.create(DetailsModal, {appointment: appointment});
        this.modal.present();
    }
}

And in the app.component.ts, I used the platform.registerBackButtonAction method to register a callback that will be called everytime the back button is clicked. Inside it I check if the function backButtonAction exists in the current page and call it, if it doesn't exists, just go to the main/first tab.

One could simplify this if they didn't need to perform customized actions for every page. You could just pop or exit the app.

I did it this way because I needed to check if the modal was open on this particular page.

Code:

  platform.registerBackButtonAction(() => {
    let nav = app.getActiveNav();
    let activeView: ViewController = nav.getActive();

    if(activeView != null){
      if(nav.canGoBack()) {
        nav.pop();
      }else if (typeof activeView.instance.backButtonAction === 'function')
        activeView.instance.backButtonAction();
      else nav.parent.select(0); // goes to the first tab
    }
  });

if the current page is the first tab, the app closes (as defined in the backButtonAction method).