NullPointerException Location.getLongitude（）

Question

我想在我的片段中獲取onCreateView（）中的當前位置。我在獲取當前經度的行上得到空指針異常。我究竟做錯了什麼？

final LocationListener locationListener = new LocationListener() 
     { 
      @Override 
      public void onLocationChanged(Location currentLocation) 
      { 
       latitude = currentLocation.getLatitude(); 
       longitude = currentLocation.getLongitude(); 
      } 
      public void onProviderDisabled(String provider) 
      { 

      } 
      public void onProviderEnabled(String provider) 
      { 

      } 
      public void onStatusChanged(String provider, int status, Bundle extras) 
      { 

      } 
     }; 

     lm = (LocationManager)getActivity().getSystemService(Context.LOCATION_SERVICE); 
     lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 100, 1, locationListener); 
     location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
     longitude = location.getLongitude(); 
     latitude = location.getLatitude(); 

Answer 1

使用NETWORK_PROVIDER得到的位置，因爲很多時候GPS將給空的經度和緯度

m_locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER,0,0, this); 
    m_location = m_locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER); 

添加下面的權限清單

<uses-permission android:name="android.permission.INTERNET" /> 
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> 
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> 
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> 
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" /> 
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> 
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" /> 

Answer 2

你沒錯。

location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER); 

該方法只返回最後已知位置。它不計算位置。當沒有舊的位置記錄時它將爲空。您在代碼中請求更新。所以，如果你需要，你可以等到你得到位置更新。

Answer 3

您是否在談論回撥以外的location.getLongitude()通話？ 如果這是你正在談論的，那麼不能保證手機將具有GPS或啓用GPS。在任何一個場景中，你都會得到一個空的迴應。雖然很難滿足所有情況，但最好從網絡提供商那裏獲得位置，這很可能在那裏。另外，我會使用Criteria構建器來獲得更適合您需求的連接。例如，如果您只想知道用戶在哪個城市，GPS就會被殺死。

//force last known location from network provider 
String providerName = LocationManager.NETWORK_PROVIDER; 
if (mLocationManager.isProviderEnabled(providerName)) { 
    Location lastLocation = mLocationManager.getLastKnownLocation(providerName); 
} 

//get high accuracy provider 
providerName = mLocationManager.getBestProvider(createMediumCriteria(), true); 
if (providerName == null) { 
    // get low accuracy provider 
    providerName = mLocationManager.getBestProvider(createLowCriteria(), true); 
} 

if (providerName == null) { 
    //get low accuracy even if its disabled 
    providerName = mLocationManager.getBestProvider(createLowCriteria(), false); 
} 

if (providerName != null && mLocationManager.isProviderEnabled(providerName)) { 

    Location lastLocation = mLocationManager.getLastKnownLocation(providerName); 

    if (lastLocation != null) { 
    onLocationChanged(lastLocation); 
    } 
    //else { 
    //timeout after 30 seconds. 
    if (!sLocationHandler.hasMessages(MSG_UNREGISTER)) { 
    sLocationHandler.sendEmptyMessageDelayed(MSG_UNREGISTER, 30000); 
    } 

    //LocationProvider provider = locMgr.getProvider(providerName); 
    // using low accuracy provider... to listen for updates 
    mLocationManager.requestLocationUpdates(providerName, 0, 0f, this); 
    //} 

的標準建設者將是這樣的：

/** 
    * this criteria will settle for less accuracy, high power, and cost 
    */ 
    public static Criteria createLowCriteria() { 

    Criteria c = new Criteria(); 
    c.setAccuracy(Criteria.ACCURACY_LOW); 
    c.setAltitudeRequired(false); 
    c.setBearingRequired(false); 
    c.setSpeedRequired(false); 
    c.setCostAllowed(true); 
    c.setPowerRequirement(Criteria.POWER_LOW); 
    return c; 
    } 

    /** 
    * this criteria needs high accuracy, high power, and cost 
    */ 
    public static Criteria createMediumCriteria() { 

    Criteria c = new Criteria(); 
    c.setAccuracy(Criteria.ACCURACY_MEDIUM); 
    c.setAltitudeRequired(false); 
    c.setBearingRequired(false); 
    c.setSpeedRequired(false); 
    c.setCostAllowed(true); 
    c.setPowerRequirement(Criteria.POWER_HIGH); 
    return c; 
    }