如何使用Xamarin.Forms和GoogleMaps / GeoLocation

Question

I am writing a Xamarin.Forms PCL app, to support iOS and Android OS for my app.

In the root project, I have a view containing a ViewList and a map (from Xamarin.Forms.Maps).

I learnt I have to use CustomRenderer for each platform to add customized behavior. What I am trying to achieve to add a LocationManager/GeoLocation to identify the users position via GPS and show his position with a pin/marker. Additionally to that, I get positions from the root project of several persons which pins must also be shown within the map.

Should I have to use an interface exporting functionality or use an appropriate custom map renderer?

I have no idea to achieve that, the examples at the Xamarin.Forms website and research within Stackoverflow do not give a hint.

Here is some code I have so far (extract):

using System;
using Awesome;
using Xamarin.Forms;
using Xamarin.Forms.Maps;
using System.Collections.ObjectModel;
using System.Collections.Generic;
using Plugin.Geolocator;
using System.Threading.Tasks;

namespace KiLa
{
    public class KidsFinder : ContentPage, ITabPage
    {
        public string TabIcon => FontAwesome.FAMapMarker;
        public string SelectedTabIcon => FontAwesome.FAMapMarker;
        private Boolean _showKidsList;
        private ListView _listView;
        public ObservableCollection<KidsViewModel> kidsList = new ObservableCollection<KidsViewModel>();

        public KidsFinder ()
        {

            Title = "KidsFinder";
            // Define listView

            // Any near/identified kids? Mockup
            // TODO: get real data
            Boolean kidsPresent = true;

            // Initial height of map
            double mapHeight = 300.0;

            // coordinates of Beuth Hochschule, Haus Gauss
            double latitude = 52.543100;
            double longitude = 13.351450;

            // Show/hide kidsList (listView)
            //Boolean showKidsList = false;
            _showKidsList = false;

            // Define toggleButton
            Button toggleButton = new Button();
            toggleButton.Text = "Verstecke Liste";

            toggleButton.Clicked += new EventHandler(OnClickEvent);

            if(kidsPresent == true) 
            {
                toggleButton.IsVisible = true;
                mapHeight = 200.0;
                _showKidsList = true;
            } else 
                {
                    toggleButton.IsVisible = false;
                    mapHeight = 300.0;
                    _showKidsList = false;
                }

            // Mockup some kids
            Position pos1 = new Position(latitude + 0.002, longitude + 0.002);
            Position pos2 = new Position (latitude - 0.002, longitude - 0.002);
            kidsList.Add(new KidsViewModel{Name="Tim", ActualPositon=pos1, DistanceToEducator=5.4});
            kidsList.Add(new KidsViewModel{Name="Sabine", ActualPositon=pos2, DistanceToEducator=20.4});

            _listView = new ListView();
            _listView.ItemsSource = kidsList;
            //listView.VerticalOptions = LayoutOptions.FillAndExpand;
            _listView.ItemTemplate = new DataTemplate (typeof(KidsCustomCell));
            _listView.RowHeight = 50;

            if (_showKidsList == false) {
                _listView.IsVisible = false;
            } else {
                _listView.IsVisible = true;
            }

            // Define mapView
            var kidsMap = new KidsMap ();
            kidsMap.MapType = MapType.Street;
            kidsMap.WidthRequest = 960;
            kidsMap.HeightRequest = mapHeight;
            kidsMap.MoveToRegion(MapSpan.FromCenterAndRadius(new Position(latitude,longitude), Distance.FromMiles(0.3)));

            // Set label of pins with kids names,
            foreach (KidsViewModel kvm in kidsList) {
                Pin pin = new Pin() {
                    Label = kvm.Name,
                    Position = kvm.ActualPositon
                };
                    kidsMap.Pins.Add(pin);
            }

Answer 1

You should use GetLocation and declare the permissions necessary to use the LocationServices

[assembly: UsesPermission(Manifest.Permission.AccessFineLocation)]
[assembly: UsesPermission(Manifest.Permission.AccessCoarseLocation)]

This is not strictly necessary for obtaining the GPS coordinates of the device, but this example will attempt to provide a street address for the current location:

[assembly: UsesPermission(Manifest.Permission.Internet)]

Add a method called InitializeLocationManager to activity

void InitializeLocationManager()
{
_locationManager = (LocationManager) GetSystemService(LocationService);
Criteria criteriaForLocationService = new Criteria
{
Accuracy = Accuracy.Fine
};
IList<string> acceptableLocationProviders = _locationManager.GetProviders(criteriaForLocationService, true);

if (acceptableLocationProviders.Any())
{
_locationProvider = acceptableLocationProviders.First();
}
 else
{
_locationProvider = string.Empty;
}
Log.Debug(TAG, "Using " + _locationProvider + ".");
}

The LocationManager class will listen for GPS updates from the device and notify the application by way of events. In this example we ask Android for the best location provider that matches a given set of Criteria and provide that provider to LocationManager.

For more details how to get current location using Xamarin Forms, follow this link: https://developer.xamarin.com/recipes/android/os_device_resources/gps/get_current_device_location/