Xamarin, Android and starting a service at device boot

In my previous post called Xamarin: how to Start an Application at Device Boot in Android, I explained how you can change your Android Xamarin's project to launch your app at the device boot.

It is a good start but my problem was a bit more complex. I want to create a background service to track the geolocation of a device. I googled a lot to find a solution without a great success. Then I started to implement my code with some tests. Finally, I found a good way and I'm sharing with you it.

Create a Broadcast Receiver

What is a Broadcast Receiver

A broadcast receiver is a component that responds to system-wide broadcast announcements. Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured. Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work.

How to implement a Broadcast Receiver

I show you now two implementations of it:

  • BootReceiver: this receiver is responsible to do something when a device starts. For that, we have to allow the app to read this event. In your AndroidManifest.xml you must add a permission called RECEIVE_BOOT_COMPLETED.
  • AirplaneModeReceiver: this receiver filters only the broadcast for ActionAirplaneModeChanged.

I start to show you the second one because it is more simple.

	[BroadcastReceiver]
    [IntentFilter(new[] { Android.Content.Intent.ActionAirplaneModeChanged })]
	public class AirplaneModeReceiver : BroadcastReceiver
	{
		private static readonly string TAG = typeof(AirplaneModeReceiver).FullName;

		public override void OnReceive(Context context, Intent intent)
		{
			Log.WriteLine(LogPriority.Debug, TAG, "AirplaneModeReceiver OnReceive Mode " + 
                          isAirplaneModeOn(context));
		}

		private static bool isAirplaneModeOn(Context context)
		{
			var airplane = Android.Provider.Settings.Global.GetInt(context.ContentResolver, 
                           Android.Provider.Settings.Global.AirplaneModeOn);
			return airplane != 0;
		}
	}

Although you can find a lot of posts where people said that you have to declare your broadcast in the AndroidManifest, I discover if I add the broadcast in the AndroidManifest, the broadcast won't work.

This is the first broadcast. Basically when a user taps on AirPlaneMode, this broadcast receives the status with isAirplaneModeOn function and writes this change in the logs.

BootReceiver is more interesting. When a device is booting, this broadcast starts a service to track the position. Also, in my code you find TimeService: I use this service to check if the service is starting properly and the notification is working and updating.

    [BroadcastReceiver]
    [IntentFilter(new[] { Android.Content.Intent.ActionBootCompleted })]
    public class BootReceiver : BroadcastReceiver
    {
        private static readonly string TAG = typeof(BootReceiver).FullName;

        public override void OnReceive(Context context, Intent intent)
        {
            Log.WriteLine(LogPriority.Debug, TAG, "BootReceiver OnReceive");

            Intent i = new Intent(context, typeof(GPSService));
            i.AddFlags(ActivityFlags.NewTask);
            context.StartService(i);
            Log.WriteLine(LogPriority.Debug, TAG, 
                          "BootReceiver OnReceive LocationService started");

			i = new Intent(context, typeof(TimerService));
			i.AddFlags(ActivityFlags.NewTask);
			context.StartService(i);
			Log.WriteLine(LogPriority.Debug, TAG, 
                          "BootReceiver OnReceive TimerService started");
		}
    }

The interesting part of this code is when I start a service. Basically, I define a new Intent with the type of service I want to call, then I start the service with the context.

Although you find a lot of posts on line, the right way to define a service in your AndroidManifest is the following:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" android:versionName="1.0" package="pro.wordbank.app.locationtest">
	<uses-sdk android:minSdkVersion="15" />
	<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
	<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
	<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
	<uses-permission android:name="android.permission.INTERNET" />
	<application android:label="LocationTest">
		<service android:name=".TimerService" />
        <service android:name=".LocationService" />
	</application>
</manifest>

I have publish a complete solution of that on GitHub. Happy coding!

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