Xamarin.Forms DependencyService难度越来越位置 [英] Xamarin.Forms DependencyService difficulty getting location

问题描述

于是后，终于让我的头周围Xamarin.Forms DependencyService我还差点就返回设备的当前位置。

So after finally getting my head around Xamarin.Forms DependencyService I have nearly got it returning the device's current location.

我的界面

public interface ICurrentLocation
{
    MyLocation SetCurrentLocation();
}

MyLocation

MyLocation

public class MyLocation
{
    public double Latitude {get; set;}
    public double Longitude{get; set;}
}

调用它的行

MyLocation location = DependencyService.Get<ICurrentLocation>().SetCurrentLocation();

和在实现Geolocation类Xamarin.Mobile的Andr​​oid项目的CurrentLocation类

and in the CurrentLocation class in the Android project that implements the Geolocation class of Xamarin.Mobile

[assembly: Dependency(typeof(CurrentLocation))]
namespace MyCockburn.Droid
{

    public class CurrentLocation : Activity, ICurrentLocation

        Geolocator locator;
        Position position = new Position();
        MyLocation location;

        public MyLocation SetCurrentLocation()
        {
            GetPosition();
            location = new MyLocation()
            {
                Latitude = position.Latitude,
                Longitude = position.Longitude
            };


            return location;
       }

       async void GetPosition()
       {
           try
           {
                 locator = new Geolocator(this) { DesiredAccuracy = 50 };
                 if (locator.IsListening != true)
                       locator.StartListening(minTime: 1000, minDistance: 0);

                 position = await locator.GetPositionAsync(timeout: 20000);

           }
           catch (Exception e)
           {
               Log.Debug("GeolocatorError", e.ToString());
           }
       }
   }

我的问题似乎是在返回位置位置持有的经度和纬度之前

my problem seems to be that is returning location before position holds the longitude and latitude

我希望我的错误已经昭然若揭了。

I am hoping my mistake is glaringly obvious

编辑：code的作品，如果我运行它作为一个正常的Andr​​oid活动

the code works if I run it as a normal Android Activity

推荐答案

我会做一个轻微的修改，因为最好的做法是要么做异步或无。当您尝试从异步方法从非异步方法返回的结果，你可以遇到了问题，死锁。此外，由于在调用为getPosition方法时不使用计谋关键字，你取回一个任务，但不检查时，操作完成。我建议稍微修改您的code这样。

I would do a slight modification since best practice is to either do all async or none. When you try to return the result from an async method from a non async method you can run into problems with deadlocks. Also, since you aren't using the await keyword when calling the GetPosition method, you are getting back a Task, but aren't checking when the operation is complete. I suggest slightly modifying your code as such.

public interface ICurrentLocation {
    Task<MyLocation> GetCurrentLocation();
}

public async Task<MyLocation> GetCurrentLocation()
{
    var position = await GetPosition();
    return new MyLocation()
    {
        Latitude = position.Latitude,
        Longitude = position.Longitude
    };
}

async Task<Location> GetPosition()
{
    try
    {
          locator = new Geolocator(this) { DesiredAccuracy = 50 };
          if (locator.IsListening != true)
                locator.StartListening(minTime: 1000, minDistance: 0);

          return await locator.GetPositionAsync(timeout: 20000);

    }
    catch (Exception e)
    {
        Log.Debug("GeolocatorError", e.ToString());
    }
}

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