How to prevent multiple watchLocation listeners ?

[Syler921]

Hi,

Is there some option to stop all active watchLocation listeners started from the app ?

In my case I have component which starts watchLocation listener every time when is visited. The problem is the previous listeners don't stop to listen for gps location ( and i have multiple active listeners for gps location ).

How can i stop them without to know their watch IDs ?

I tried with simple check :

               if ( !this.watchId ) {
                    this.watchId = geolocation.watchLocation(this.locationReceived, this.error, {
                        desiredAccuracy: 20,
                        updateDistance: 0,
                        minimumUpdateTime: 15000,
                        maximumAge: 6000
                    });
                }

But every time this watchID is different for each new visit in the component and accordingly it`s not created ( this doesn't work ) .

Thanks for help !

[DimitarTachev]

Hi @Syler921,

It's a very nice idea. We could add something like clearAllWatchIds() similar to the Demo App logic. I've labeled that with the 'good first time' label.

[briandilley]

here:

import {Injectable} from "@angular/core";
import {Observable} from "rxjs/Observable";
import {Subscription} from "rxjs/Subscription";
import {interval} from 'rxjs/observable/interval'
import {timer} from 'rxjs/observable/timer'
import {delayWhen, distinctUntilChanged, flatMap, map, retryWhen, share, switchMap, tap} from 'rxjs/operators'

import {clearWatch, enableLocationRequest, Location as GPSLocation, watchLocation} from "nativescript-geolocation";
import {Accuracy} from "tns-core-modules/ui/enums";
import {Analytics} from "../utils/analytics";

export const DEFAULT_OPTIONS = {
  desiredAccuracy: Accuracy.high,
  minimumUpdateTime: 1000,
  iosAllowsBackgroundLocationUpdates: true
};

export {Location as GPSLocation} from "nativescript-geolocation";

@Injectable()
export class LocationService {

  private _lastLocation: GPSLocation;

  private locationEvents: Observable<GPSLocation>;

  public constructor() {
    this.locationEvents = this.askForLocationPermissions()
      .pipe(
        flatMap(() => new Observable((sub) => {
          let watchId = -1;
          try {
            watchId = watchLocation(
              (loc) => {
                this._lastLocation = loc;
                console.log(`NEW! lat: ${loc.latitude} lon: ${loc.longitude}`)
                sub.next(loc);
              },
              (error) => {
                sub.error(error);
              },
              DEFAULT_OPTIONS);
            console.info(`[watchLocation ${watchId}] Subscribed`);

          } catch(error) {
            sub.error(error);
          }

          return () => {
            if (watchId != -1) {
              console.info(`[watchLocation ${watchId}] Unsubscribed`);
              clearWatch(watchId);
            }
          };
        })),
        switchMap((loc: GPSLocation) => interval(1000)
          .pipe(
            map(() => loc),
            tap((loc) => console.log(`lat: ${loc.latitude} lon: ${loc.longitude}`)))),
        share());
  }

  public get lastLocation(): GPSLocation {
    return this._lastLocation;
  }

  /**
   * Keeps the location updated by calling the given callback, the
   * subscription is returned.
   */
  public keepLocationUpdated(callback: (loc: GPSLocation) => void): Subscription {
      return this.watchLocation()
        .pipe(
          retryWhen((errors) => errors
            .pipe(
              tap((error) => Analytics.logError(error, "Error in keepLocationUpdated, attempting retry in 1 second")),
              delayWhen(() => timer(1000)))),
          distinctUntilChanged((x, y) => x.latitude !== y.latitude || x.longitude !== y.longitude))
        .subscribe(
          (loc) => callback(loc),
          (error) => Analytics.logError(error, "Fatal error in keepLocationUpdated"));
  }

  /**
   * Begins watching the current location.
   */
  public watchLocation(): Observable<GPSLocation> {
    return this.locationEvents;
  }

  /**
   * Asks for location permissions, returns either true or an error.
   */
  public askForLocationPermissions(): Observable<boolean> {
    return new Observable((sub) => {
      enableLocationRequest()
        .then(() => {
          sub.next(true);
          sub.complete();
        })
        .catch(() => sub.error(new Error('Location services not enabled')));
    });
  }

}

[devyaz]

@briandilley how about a vanilla js example

[briandilley]

@devyaz - no

On Sat, Sep 22, 2018, 2:16 AM devyaz [email protected] wrote:

@briandilley https://github.com/briandilley how about a vanilla js example

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/NativeScript/nativescript-geolocation/issues/46#issuecomment-423729747, or mute the thread https://github.com/notifications/unsubscribe-auth/ABBNz4Nun_9ZcB8lz0lMQQJ34ezeACR1ks5udgAHgaJpZM4LZP2f .

[StefanAleksik]

Hey I am quite new to NS and Android and I also need this feature as well. I am thinking of making an improvisation using a for loop. Since the watchID is provided via increment, I am thinking of iterating for all previous values that were used for the watchID and passing them in clearWatch. The problem here is that I need to first get the watchID (which means starting a watchLocation) and afterwards I can clear all previous watchLocation listeners. Is there a way to get the watchID (the current value of watchIdCounter) without starting an watchLocation.

Another option would be to get access to the locationListeners object and remove all existing listeners.