使用GPS定位系統服務依賴項注入

Question

我希望使用Xamarin的依賴項注入獲取特定於平台的位置詳細信息，但遇到了問題。 錯誤做的可能性更大。

這是我當前的設置：

nuMaps /接口/ ILocationService.cs

using Xamarin.Forms.Maps;

namespace nuMaps
{
    public interface ILocationService
    {
        void initLocationService();
        Position getCurrentPosition();
    }
}

nuMaps / nuMaps.Droid /接口/ LocationService.cs

using System;
using nuMaps;
using nuMaps.Droid;
using Xamarin.Forms.Maps;
using Android.App;
using Android.Gms.Common;
using Android.Gms.Common.Apis;
using Android.Gms.Location;
using Android.Locations;
using Android.Widget;

[assembly: Xamarin.Forms.Dependency (typeof (LocationService))]

namespace nuMaps.Droid
{
    public class LocationService : Java.Lang.Object, ILocationService, IGoogleApiClientConnectionCallbacks, IGoogleApiClientOnConnectionFailedListener, Android.Gms.Location.ILocationListener
    {
        readonly IGoogleApiClient _googleApiClient;
        readonly LocationRequest _locRequest;
        Position _currentPosition;
        Location _currentLocation;

        public LocationService()
        {
            Console.WriteLine ("LocationService constructor");
            _currentPosition = new Position (0, 0);

            _googleApiClient = new GoogleApiClientBuilder (Xamarin.Forms.Forms.Context)
                .AddApi (LocationServices.Api)
                .AddConnectionCallbacks (this)
                .AddOnConnectionFailedListener (this)
                .Build ();

            _locRequest = new LocationRequest ();
        }

        #region ILocationService implementation

        public void initLocationService()
        {
            _googleApiClient.Connect ();
        }

        public Position getCurrentPosition ()
        {
            if (_googleApiClient.IsConnected) {
                _currentLocation = LocationServices.FusedLocationApi.GetLastLocation (_googleApiClient);
                _currentPosition = new Position (_currentLocation.Latitude, _currentLocation.Longitude);
            }

            _googleApiClient.Disconnect ();

            return new Position (_currentLocation.Latitude, _currentLocation.Longitude);
        }

        #endregion
        public void OnLocationChanged(Location l)
        {
            Console.WriteLine ("OnLocationChanged");
            _currentLocation = l;
        }

        public void OnConnectionFailed (ConnectionResult result)
        {
            Console.WriteLine ("ConnectionFailed");
        }

        #region IGoogleApiClientConnectionCallbacks implementation
        public void OnConnected (Android.OS.Bundle connectionHint)
        {
            Console.WriteLine ("OnConnected");

            if (!_googleApiClient.IsConnected)
                LocationServices.FusedLocationApi.RequestLocationUpdates (_googleApiClient, _locRequest, this);

            _currentLocation = LocationServices.FusedLocationApi.GetLastLocation (_googleApiClient);
        }
        public void OnConnectionSuspended (int cause)
        {
            Console.WriteLine ("OnConnectionSuspended");
        }
        #endregion
    }
}

在nuMaps / Views / MapPage.xaml.cs中的用法

using Xamarin.Forms;
using Xamarin.Forms.Maps;
using System;
using System.Diagnostics;

namespace nuMaps
{
    public partial class MapPage : ContentPage
    {

        public MapPage ()
        {
            InitializeComponent ();
            Position p = DependencyService.Get<ILocationService>().getCurrentPosition();
            MyMap.MoveToRegion (
                MapSpan.FromCenterAndRadius (
                    p, Distance.FromMiles (1)
                )
            );
        }
    }
}

nuMaps /瀏覽/ Loginpage.xaml.cs

using System;
using Xamarin.Forms;
using nuMaps;

namespace nuMaps
{
    public partial class LoginPage : ContentPage
    {
        public LoginPage ()
        {
            InitializeComponent ();

            /*
             * Init platform specific location service.
             * TODO: This *shouldn't* need to happen, but we don't get location information until
             * the OnConnected callback happens which is too slow to put in getCurrentLocation method.
             */

             DependencyService.Get<ILocationService>().initLocationService();
        }
    }
}

Answer 1

我相信問題出在您的ILocationService實現中。

我將刪除實現活動（為什么要使用OnCreate？），並查看http://developer.xamarin.com/guides/android/platform_features/maps_and_location/location/ 。

我建議你在Android上獲取GPS位置通過谷歌API的發揮，這將需要實施ILocationListener ， IGoogleApiClientConnectionCallbacks和IGoogleApiClientOnConnectionFailedListener 。 希望有幫助！

編輯評論：

如果問題LocationService是最新的，我沒有看到你正在實施IGoogleApiClientConnectionCallbacks或ILocationListener 。 可能是因為地圖頁使用的是gps， GetLastKnownLocation起作用了，因為最近已經獲得了位置。

GPS位置請求是一個異步操作IGoogleApiClientConnectionCallbacks的方法IGoogleApiClientConnectionCallbacks是OnConnected，您應在其中調用類似以下內容的方法：

LocationServices.FusedLocationApi.RequestLocationUpdates(googleApiClient, locationRequest, this);

這將主動請求位置更新，然后在返回位置更新時觸發OnLocationChanged(Location location) 。 這些都是異步的，因此您可能需要在LocationService中公開這些事件並進行訂閱。

Answer 2

您可以嘗試TinyIoC，而不是Xamarin Dependency Service。 它適用於特定於平台的實現，例如定位服務。

也許Xamarin Dependency Service可以用於這些類型的事情，但是到目前為止，我僅將其用於自定義渲染器。 對於更多基於服務的內容，我使用TinyIoC。