Android Tutorial Geofence - Monitoring a region in the background

Erel · Oct 8, 2017

Geofencing is an Android feature that allows your app to be notified when the user enters or exits a monitored region.

The nice thing about this feature is that your app doesn't need to run for monitoring to work.
It will be started automatically when needed.

The GeofenceService uses JavaObject to implement the Geofencing API: https://developer.android.com/training/location/geofencing.html

Configuration steps
- Add GeofenceService from the example project to your app.
- Add this code to the manifest editor:

B4X:

AddPermission(android.permission.ACCESS_FINE_LOCATION)
CreateResourceFromFile(Macro, FirebaseAnalytics.GooglePlayBase)

- Add geofences regions with code such as:

B4X:

'Geofence regions are defined as a circle with a center point and radius.
Sub AddGeofence
   rp.CheckAndRequest(rp.PERMISSION_ACCESS_FINE_LOCATION)
   Wait For Activity_PermissionResult (Permission As String, Result As Boolean)
   If Result Then
       Dim geo As Geofence
       geo.Initialize
       geo.Id = "Test1"
       geo.Center.Initialize2(32.8372, 35.2698) 'change location!
       geo.RadiusMeters = 100
       geo.ExpirationMs = DateTime.TicksPerDay 'expire after one day
       CallSubDelayed3(GeofenceService, "AddGeofence", Me, geo)
       Wait For Geofence_Added (Success As Boolean)
       Log("Geofence added: " & Success)
   End If
End Sub

- Add the event subs to the starter service:

B4X:

Public Sub Geofence_Enter (Id As String)
   Dim n As Notification
   n.Initialize
   n.Icon = "icon"
   n.SetInfo("Enter: " & Id, "Enter", Main)
   n.Notify(1)
   ToastMessageShow("Enter: " & Id, True)
End Sub

Public Sub Geofence_Exit (Id As String)
   Log("Exit: " & Id)
   ToastMessageShow("Exit: " & Id, True)
   Dim n As Notification
   n.Initialize
   n.Icon = "icon"
   n.SetInfo("Exit: " & Id, "Exit", Main)
   n.Notify(2)
End Sub

- Add to the main module:

B4X:

#AdditionalJar: com.google.android.gms:play-services-location

Note that monitored regions are cleared when the device is restarted. You can add another service with #StartAtBoot set to true and add the regions there.

Updates:

- Uses a receiver instead of service. Services will fail on newer version of Android.

Beja · Oct 10, 2017

I found a workaround, that one can define a series of overlapped circular fences with radius of .5 * the desired rectangular width.. The number if fences corresponds to the desired resolution of the rectangle.

Erel · Oct 10, 2017

The three formats are supported. The code from the example uses the first format.

Beja · Oct 10, 2017

Erel said:
The three formats are supported. The code from the example uses the first format.

Thanks Erel

Beja · Nov 25, 2017

Hi Erel,
Today I tried to run the example and on one phone it just closed without notification, and on another one it said "Unfortunately, B4A Example has stopped. Open app again"
any help appreciated.
Using B4A 7.01

Erel · Nov 26, 2017

You will need to check the logs and find the error message.

DonManfred · Nov 26, 2017

check the unfiltered logs also

Beja · Nov 26, 2017

Ok Don, sorry was looking to the wrong place.

Christian García S. · Dec 12, 2017

Hello, It have been implented this library in a marketing project and works perfect, but I need this library for a logistic project.

I have a question, the event Geofence is launched one time when the user enter to the geofence.

There are a way for asking which is geofence I am inside, is for validation porpuses, I know I can make a variable and save this information.

For example if the app is closed or the phone is restarted and I receive the notification, I can not use this variable for some validation, because the event is only triggered one time.

Or can you give me an idea how I can validate location??

Thanks for your help.

Regards,
Christian

DonManfred · Dec 12, 2017

Christian García S. said:
There are a way for asking which is geofence I am inside

The event which raise contains the ID of the Fence you entered....
It is the ID you set when creating the Fence.

B4X:

   Dim geo As Geofence
   geo.Initialize
   geo.Id = "Test1" ' ID is here....
   geo.Center.Initialize2(32.8372, 35.2698) 'change location!
   geo.RadiusMeters = 100
   geo.ExpirationMs = DateTime.TicksPerDay 'expire after one day

B4X:

Public Sub Geofence_Enter (Id As String)
   Log("Enter: " & Id)
End Sub

Public Sub Geofence_Exit (Id As String)
   Log("Exit: " & Id)
End Sub

BillMeyer · Mar 5, 2018

Good Day,

I have a situation where I place a GeoFence at an Accident Scene. The time that it takes for the Accident to be cleared up is variable. After the clean up I no longer need the GeoFence and need to expire it.

Will it suffice to re-write/over write the fence and then just alter the ExpirationsMs to DateTime.Now ? or is there another way of doing this ?

If I need to create a new thread, I will, please advise.

Erel · Mar 5, 2018

You can add this sub to the GeofenceService:

B4X:

Public Sub RemoveGeofence(geo As Geofence)
 Dim g As List
 g.Initialize
 g.Add(geo.Id)
 client.RunMethod("removeGeofences", Array(g))
End Sub

Erel · Dec 30, 2018

I've updated the example with targetSdkVersion set to 26. Please try it.

Johan Hormaza · Apr 21, 2021

I have this problem on Android 8.1

--------- beginning of crash
--------- beginning of system
--------- beginning of main
*** Service (starter) Create ***
** Service (starter) Start **
** Activity (main) Create, isFirst = true **
** Activity (main) Resume **
*** Service (geofenceservice) Create ***
** Service (geofenceservice) Start **
com.google.android.gms.common.api.ApiException: 1000:
Geofence added: false

And in a Xiaomi Redmi Note 8 Android 9 it does not tell me if I am inside or outside the Geofence

Erel · Apr 22, 2021

1000 = GEOFENCE_NOT_AVAILABLE

GeofenceStatusCodes | Google Play services | Google for Developers

developers.google.com

Make sure that location services are enabled. For further discussion please start a new thread.

Erel · Feb 1, 2023

Example was updated. It is now based on B4XPages and a receiver instead of a service.

Android Tutorial Geofence - Monitoring a region in the background

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