My Hardware 'Back Button Action' is not working in Ionic 4

Question

I am working in my Ionic 4 app and When the user clicks 2 times on the mobile back button, then it should close the app but this is not happening.

This is my app.component.ts:

lastTimeBackPress = 0;
timePeriodToExit = 2000;
@ViewChildren(IonRouterOutlet) routerOutlets: QueryList<IonRouterOutlet>;

constructor(){
this.backButtonEvent();
}

backButtonEvent() {
    document.addEventListener("backbutton", () => { 
      this.routerOutlets.forEach((outlet: IonRouterOutlet) => {
        if (outlet && outlet.canGoBack()) {
            outlet.pop();
        } else if (this.router.url === '/tabs/tab1') {
          if (new Date().getTime() - this.lastTimeBackPress < this.timePeriodToExit) {
            navigator['app'].exitApp(); //Exit from app
            } else {
            this.presentAlertConfirm();
            this.lastTimeBackPress = new Date().getTime();
          }
          // navigator['app'].exitApp(); // work for ionic 4
        }
      });
    });
  }

  async presentAlertConfirm() {
    const alert = await this.alertController.create({
      // header: 'Confirm!',
      message: 'Are you sure you want to exit the app?',
      buttons: [
        {
          text: 'Cancel',
          role: 'cancel',
          cssClass: 'secondary',
          handler: (blah) => {
          }
        }, {
          text: 'Close App',
          handler: () => {
            navigator['app'].exitApp();
          }
        }
      ]
    });

    await alert.present();
  }

This is working when I am on front page(Tab1) and when I am on the other tabs it is not working and not going to the front page.

I think the problem is in my (outlet && outlet.canGoBack()) because this is not working. I am using the tab theme and Can I send the route to the main tab when the user is no other tabs and clicks the hardware back button.

I am using Ionic 4 tab theme.

Any help is much appreciated.

Answer 1

Try This:

lastTimeBackPress = 0;
timePeriodToExit = 2000;
@ViewChildren(IonRouterOutlet) routerOutlets: QueryList < IonRouterOutlet > ;
backButtonEvent() {
  document.addEventListener("backbutton", async() => {
    try {
      const element = await this.modalCtrl.getTop();
      if (element) {
        element.dismiss();
        return;
      }
    } catch (error) {
      console.log(error);
    }
    this.routerOutlets.forEach(async(outlet: IonRouterOutlet) => {
      if (this.router.url != '/tabs/tab1') {
        await this.router.navigate(['/tabs/tab1']);
      } else if (this.router.url === '/tabs/tab1') {
        if (new Date().getTime() - this.lastTimeBackPress >= this.timePeriodToExit) {
          await this.presentAlertConfirm();
          this.lastTimeBackPress = new Date().getTime();
        }
        navigator['app'].exitApp(); // work for ionic 4
      }
    });
  });
}

And call this function in the constructor. This solved my problem because I am using the tabs theme and outlet.pop(); was not working. So I tried this method.