fix: added pending callbacks mechanism to solve npe crash

[shubhamguptadream11]

Overview

Solves this issue:

• Android crash when I set the locationProvider to playServices(Some times) #241

Crash Log

Fatal Exception: java.lang.NullPointerException: Listener must not be null
at com.google.android.gms.common.internal.Preconditions.checkNotNull(com.google.android.gms:play-services-basement@@18.1.0:2)
at com.google.android.gms.common.api.internal.ListenerHolders.createListenerKey(com.google.android.gms:play-services-base@@18.0.1:1)
at com.google.android.gms.location.FusedLocationProviderClient.removeLocationUpdates(com.google.android.gms:play-services-location@@20.0.0:6)
at com.reactnativecommunity.geolocation.PlayServicesLocationManager$1.onLocationResult(PlayServicesLocationManager.java:74)
at com.google.android.gms.internal.location.zzaw.notifyListener(com.google.android.gms:play-services-location@@20.0.0:2)
at com.google.android.gms.common.api.internal.ListenerHolder.zaa(com.google.android.gms:play-services-base@@18.0.1:2)
at com.google.android.gms.common.api.internal.zacb.run(:4)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:8057)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)

It is easily reproducible with example app in react-native-geolcation repo.
Reproducer App: https://github.com/michalchudziak/react-native-geolocation/tree/master/example

Steps to repro:

• Clone the example app.
• Make Two Calls to getCurrentPosition

  Geolocation.getCurrentPosition(
    (info) => {
      console.log('GetCurrentPosition Success', JSON.stringify(info));
    },
    (error) => {
      console.log('GetCurrentPosition Error', JSON.stringify(error));
    },
    {
      enableHighAccuracy: true,
      maximumAge: 20 * 1000,
      timeout: 10 * 1000,
    }
  );

  Geolocation.getCurrentPosition(
    (info) => {
      console.log('GetCurrentPosition Success', JSON.stringify(info));
    },
    (error) => {
      console.log('GetCurrentPosition Error', JSON.stringify(error));
    },
    {
      enableHighAccuracy: true,
      maximumAge: 20 * 1000,
      timeout: 10 * 1000,
    }
  );

• Run the Example App:
  • Select the playServices option.
  • Click the getCurrentPosition button.
• The app crashes with the stack trace provided above.

Issue Summary

The mSingleLocationCallback gets overwritten when multiple calls to getCurrentPosition() are made before the previous call finishes. This leads to a situation where null is passed to mFusedLocationClient.removeLocationUpdates(), causing the Listener must not be null exception.

Changes Made:

• Introduced a List (mPendingLocationCallbacks) to keep track of pending location callbacks. This ensures that callbacks are properly managed and removed, preventing the crash.
• Updated getCurrentLocationData, startObserving, and stopObserving methods to handle the addition and removal of callbacks more safely and consistently.

Test Plan

Tested getCurrentPosition and watchPosition functionality.