Ionic 4 app - detect if user turns off or on gps - ionic4

Question

I would like to know how I can do to detect if during any moment of the execution of an Ionic 4 app (not only at the beginning of the app), the user manually turns off or on the GPS.
What Ionic 4 event can I hear from the GPS, to be able to alert at any time of the execution of the app if the user turned off or on the GPS?
Thank you very much and sorry for my bad English
My code on app.component.ts:
initializeApp() {
this.platform.ready().then(() => {
this.screenOrientation.lock(this.screenOrientation.ORIENTATIONS.PORTRAIT_PRIMARY);
this.platform.backButton.subscribeWithPriority(9999, () => {
document.addEventListener('backbutton', function (event) {
event.preventDefault();
event.stopPropagation();
}, false);
this.presentAlertConfirm();
});
this.geolocation.getCurrentPosition().then((resp) => {
this.global.origin = { lat: resp.coords.latitude, lng: resp.coords.longitude };
this.global.latitude = resp.coords.latitude;
this.global.longitude = resp.coords.longitude;
}).catch((error) => {
console.log('Error getting location', error);
});
let watch = this.geolocation.watchPosition();
watch.subscribe((data) => {
this.global.origin = { lat: data.coords.latitude, lng: data.coords.longitude };
this.global.latitude = data.coords.latitude;
this.global.longitude = data.coords.longitude;
}, error => {
console.log('Error getting location in WATCH', error); //error handling //
})
this.statusBar.styleDefault();
this.splashScreen.hide();
});
}

Answer 1

You have to watch for some GPS change. As proposed in the Ionic 4 documentation and as you have done correctly:
this.watch = this.geolocation.watchPosition();
this.watch.subscribe((data) => {
// usable data
}, (error) => {
// some error
}, { timeout: 30000 });
timeout: The maximum length of time (milliseconds) that is allowed to pass without receiving a set of coordinates.
And remeber to unsubscribe on destroy:
public ngOnDestroy(): void {
this.watch.unsubscribe();
}