In a previous article, I talked about setting up Prism with Shiny in a Xamarin Forms project. Now I will extend on this by adding location tracking support, which is a very common feature in enterprise applications. This article will show you how to do it step by step using Shiny.

Let’s start! 

1. Install the Shiny.Locations package

2-Create a new folder called Delegates and add GPSListener class/interface

	using System;
	using Shiny.Locations;
	namespace ShinyPrismSample.Delegates
	{
	public class GpsReadingEventArgs : EventArgs
	{
	public IGpsReading Reading { get; }
	public GpsReadingEventArgs(IGpsReading reading)
	{
	Reading = reading;
	}
	}
	public interface IGpsListener
	{
	event EventHandler<GpsReadingEventArgs> OnReadingReceived;
	}
	}

view raw IGpsListener.cs hosted with by GitHub

	using System;
	using System.Threading.Tasks;
	using Shiny.Locations;
	namespace ShinyPrismSample.Delegates
	{
	public class GpsListener : IGpsListener
	{
	public event EventHandler<GpsReadingEventArgs> OnReadingReceived;
	void UpdateReading(IGpsReading reading)
	{
	OnReadingReceived?.Invoke(this, new GpsReadingEventArgs(reading));
	}
	public class LocationDelegate : IGpsDelegate
	{
	IGpsListener _gpsListener;
	public LocationDelegate(IGpsListener gpsListener)
	{
	_gpsListener = gpsListener;
	}
	public Task OnReading(IGpsReading reading)
	{
	(_gpsListener as GpsListener)?.UpdateReading(reading);
	return Task.CompletedTask;
	}
	}
	}
	}

view raw GpsListener.cs hosted with by GitHub

This listener will handle our location updates since it has an event handler that gets invoked each time we get a new GPS reading.

3-In the ShinyAppStartup file register GPS listener as a singleton and also register Shiny GPS service.

	using Microsoft.Extensions.DependencyInjection;
	using Prism.DryIoc;
	using Shiny;
	using Shiny.Prism;
	using ShinyPrismSample.Delegates;
	using static ShinyPrismSample.Delegates.GpsListener;
	namespace ShinyPrismSample
	{
	public class ShinyAppStartup : PrismStartup
	{
	public ShinyAppStartup(): base(PrismContainerExtension.Current)
	{
	}
	protected override void ConfigureServices(IServiceCollection services)
	{
	services.AddSingleton<IGpsListener, GpsListener>();
	services.UseGps<LocationDelegate>();
	}
	}
	}

view raw ShinyAppStartup.cs hosted with by GitHub

4-In the ViewModel inject the IGpsManager and the IGpsListener.

The GPSManager has two main methods StartListener and StopListener which start/stop the GPS tracking. To gather location updates will subscribe to GpsListener event called OnReadingReceived that gets called whenever location has changed.

	using System;
	using System.ComponentModel;
	using System.Diagnostics;
	using Prism.Navigation;
	using Shiny.Locations;
	using ShinyPrismSample.Delegates;
	namespace ShinyPrismSample.ViewModels
	{
	public class MainPageViewModel : INavigatedAware, INotifyPropertyChanged, IDestructible
	{
	IGpsListener _gpsListener;
	IGpsManager _gpsManager;
	public event PropertyChangedEventHandler PropertyChanged;
	public string LocationMessage { get; set; }
	public MainPageViewModel(IGpsManager gpsManager,IGpsListener gpsListener)
	{
	_gpsManager = gpsManager;
	_gpsListener = gpsListener;
	_gpsListener.OnReadingReceived += OnReadingReceived;
	}
	void OnReadingReceived(object sender, GpsReadingEventArgs e)
	{
	LocationMessage = $"{e.Reading.Position.Latitude}, {e.Reading.Position.Longitude}";
	Debug.WriteLine(LocationMessage);
	}
	public void OnNavigatedFrom(INavigationParameters parameters)
	{
	}
	public async void OnNavigatedTo(INavigationParameters parameters)
	{
	if (_gpsManager.IsListening)
	{
	await _gpsManager.StopListener();
	}
	await _gpsManager.StartListener(new GpsRequest
	{
	UseBackground = true,
	Priority = GpsPriority.Highest,
	Interval = TimeSpan.FromSeconds(5),
	ThrottledInterval = TimeSpan.FromSeconds(3) //Should be lower than Interval
	});
	}
	public void Destroy()
	{
	_gpsListener.OnReadingReceived -= OnReadingReceived;
	}
	}
	}

view raw MainPageViewModel.cs hosted with by GitHub

5-On iOS project Info.plist add the NSLocationAlwaysUsageDescription permission and enable the location updates background mode.

	<key>NSLocationAlwaysUsageDescription</key>
	<string>Your message</string>

view raw Info.plist hosted with by GitHub

6-On Android project manifest file be sure to add the ACCESS_COARSE_LOCATION and ACCESS_FINE_LOCATION permissions 

	<?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="com.crossgeeks.shinyprismsample">
	<uses-sdk android:minSdkVersion="21" android:targetSdkVersion="28" />
	<application android:label="ShinyPrismSample.Android"></application>
	<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
	<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
	<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
	</manifest>

view raw AndroidManifest.xml hosted with by GitHub

Check the full source code here.

Happy Shining!!