LocationManager getLastKnownLocation always null

Question

我遇到問題。當我測試這個。我要求showCurrentLocation函數它總是返回null。當我發送位置後，它在模擬器中工作。但是我需要這個在電話上工作，並且你不能在DDNS窗口中發送位置。

這裏是我的代碼

public class LbsGeocodingActivity extends Activity { 

private static final long MINIMUM_DISTANCE_CHANGE_FOR_UPDATES = 1; // in Meters 
private static final long MINIMUM_TIME_BETWEEN_UPDATES = 1; // in Milliseconds 

protected LocationManager locationManager; 

protected Button retrieveLocationButton; 
protected Button stopLocationButton; 


@Override 
public void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    retrieveLocationButton = (Button) findViewById(R.id.retrieve_location_button); 
    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 

    locationManager.requestLocationUpdates(
      LocationManager.GPS_PROVIDER, 
      MINIMUM_TIME_BETWEEN_UPDATES, 
      MINIMUM_DISTANCE_CHANGE_FOR_UPDATES, 
      new MyLocationListener() 
    ); 

    retrieveLocationButton.setOnClickListener(new OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      showCurrentLocation(); 
     } 
    }); 
    /*stopLocationButton.setOnClickListener(new OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      //locationManager.removeUpdates(MyLocationListener) ;   
     } 
    }); */ 

}  

public String getMyPhoneNumber(){ 
    TelephonyManager mTelephonyMgr; 
    mTelephonyMgr = (TelephonyManager) 
    getSystemService(Context.TELEPHONY_SERVICE); 
    return mTelephonyMgr.getLine1Number(); 
} 

protected void showCurrentLocation() { 

    Criteria crit = new Criteria(); 
    crit.setAccuracy(Criteria.ACCURACY_FINE); 
    String provider = locationManager.getBestProvider(crit, true); 
    Location loc = locationManager.getLastKnownLocation(provider); 


    if (loc != null) { 
     String longi = "" + loc.getLongitude(); 
     String lat = "" + loc.getLatitude(); 
     String num = getMyPhoneNumber(); 
     String message = String.format(
       "Current Location \n Longitude: %1$s \n Latitude: %2$s \n %3$s ", 
       longi, 
       lat, 
       num  ); 
     Toast.makeText(LbsGeocodingActivity.this, message, 
       Toast.LENGTH_LONG).show(); 
    } 
    if (loc == null)Toast.makeText(LbsGeocodingActivity.this, "Null ", 
      Toast.LENGTH_LONG).show(); 
} 

private class MyLocationListener implements LocationListener { 



    public void onLocationChanged(Location loc) { 
     String longi = "" + loc.getLongitude(); 
     String lat = "" + loc.getLatitude(); 
     String num = getMyPhoneNumber(); 
     String message = String.format(
       "New Location \n Longitude: %1$s \n Latitude: %2$s \n %3$s ", 
       longi, 
       lat, 
       num    ); 
     Toast.makeText(LbsGeocodingActivity.this, message, Toast.LENGTH_LONG).show(); 
    } 

    public void onStatusChanged(String s, int i, Bundle b) { 
     Toast.makeText(LbsGeocodingActivity.this, "Provider status changed", 
       Toast.LENGTH_LONG).show(); 
    } 

    public void onProviderDisabled(String s) { 
     Toast.makeText(LbsGeocodingActivity.this, 
       "Provider disabled by the user. GPS turned off", 
       Toast.LENGTH_LONG).show(); 
    } 

    public void onProviderEnabled(String s) { 
     Toast.makeText(LbsGeocodingActivity.this, 
       "Provider enabled by the user. GPS turned on", 
       Toast.LENGTH_LONG).show(); 
    } 

} 

} 

我的權限是：FINE_LOCATION COURSE_LOCATION。

我真的只是想它，它跟蹤用戶的位置，甚至在背景..

Answer 1

您可以發送模擬地點也到你的Android設備看到 Android mock location on device?

然後除此之外我有這個問題它似乎也許從來沒有在你的設備之前的位置嘗試打開谷歌地圖，並確保你找到，然後再試一次。此外，我懷疑是因爲您第一次使用應用程序時無法訪問上次已知的位置，因爲您從未使用它，因此您首先需要找到位置，然後在下次啓動該應用程序時它將起作用。如果你想要一個快速的位置嘗試通過WiFi或手機塔找到

並確保權限設置！

Answer 2

您是否檢查過您的手機中打開了GPS，打開GPS後需要一段時間才能獲取位置更新。