Xamarin android在位置更改前獲取位置

Question

using Android.App; 
using Android.Widget; 
using Android.OS; 
using Android.Locations; 
using Android.Content; 

[Activity(Label = "Getlocation", MainLauncher = true)] 
public class MainActivity : Activity, ILocationListener 
{ 
    Button bttnGo; 
    TextView txtLoc; 
    LocationManager locMgr; 
    Location currentLocation; 
    string provider; 

    protected override void OnCreate(Bundle bundle) 
    { 
     base.OnCreate(bundle); 

     // Set our view from the "main" layout resource 
     SetContentView(Resource.Layout.Main); 

     bttnGo = FindViewById<Button>(Resource.Id.get_address_button); 
     txtLoc = FindViewById<TextView>(Resource.Id.location_text); 
     InitializeLocationManager(); 

     bttnGo.Click += BttnGo_Click; 
    } 

    async void BttnGo_Click(object sender, EventArgs e) 
    { 
     if (currentLocation == null) 
     { 
      txtLoc.Text = "No location found, try moving around"; 
     } 
     else 
     { 
      txtLoc.Text = currentLocation.ToString(); 
     } 
    } 

    private void InitializeLocationManager() 
    { 

     locMgr = (LocationManager)GetSystemService(LocationService); 

     Criteria criteriaForLocationService = new Criteria 
     { 
      Accuracy = Accuracy.Fine 
     }; 

     IList<string> acceptableLocationProviders = locMgr.GetProviders(criteriaForLocationService, true); 

     if(acceptableLocationProviders.Any()) 
     { 
      provider = acceptableLocationProviders.First(); 
     } 
     else 
     { 
      provider = string.Empty; 
     } 
    } 


    protected override void OnResume() 
    { 
     base.OnResume(); 
     locMgr.RequestLocationUpdates(provider, 2000, 0, this); 

    } 

    protected override void OnPause() 
    { 
     base.OnPause(); 
     locMgr.RemoveUpdates(this); 
    } 

    public void OnLocationChanged(Location location) 
    { 

      currentLocation = location; 
      if (currentLocation == null) 
      { 
       txtLoc.Text = "No location detected"; 

      } 
      else 
      { 
       txtLoc.Text = location.Latitude.ToString(); 
      } 

    } 

    public void OnProviderDisabled(string provider) 
    { 

    } 

    public void OnProviderEnabled(string provider) 
    { 

    } 

    public void OnStatusChanged(string provider, [GeneratedEnum] Availability status, Bundle extras) 
    { 

    } 
} 
} 

我的編碼知識很少，我只是按照教程來檢索當前位置。

我的問題是，我只能檢索實際位置更改時的位置。我知道這可能是因爲currentLocation在OnLocationChanged發生之前沒有獲得值。如何去解決這個問題？

Answer 1

Xamarin Android開位置的位置改變

之前，您可以使用GetLastKnownLocation(provider)方法來實現此功能。這裏是一個簡單的演示：

LocationManager locationManager = (LocationManager)GetSystemService(Context.LocationService); 

IList<String> lp = locationManager.AllProviders; 
foreach (String item in lp) 
{ 
    Log.Debug("TAG", "Available Location Service ：" + item); 
} 

//A class indicating the application criteria for selecting a location provider. 
Criteria criteria = new Criteria(); 
//Indicates whether the provider is allowed to incur monetary cost. 
criteria.CostAllowed = false; 
//Set desired accuracy of location Accuracy 
criteria.Accuracy = Accuracy.Coarse; 

//Returns the name of the provider that best meets the given criteria     
String providerName = locationManager.GetBestProvider(criteria, true); 
Log.Debug("8023", "------Location Service：" + providerName); 

//Directly choose a Location Provider 
//String providerName = LocationManager.GpsProvider; 

Location location = locationManager.GetLastKnownLocation(providerName); 

double lat = location.Latitude; 
double lng = location.Longitude; 

txtLoc.Text = "Latitude = " + lat + ", Longitude = " + lng;