android - getLastKnownLocation 返回 NULL

Question

我刚刚开始工作，但是当我关闭 Wifi 以查看是否可以使用 GPS 获得更准确的位置时，它现在给我带来 NullPointer 错误，我看不到为什么。

下面的代码首先被调用；

 public void onConnected(Bundle dataBundle) {
        connected = true;
        //Request an update from the location client to get current Location details
        mLocationClient.requestLocationUpdates(mLocationRequest,this);
        Toast.makeText(this, "Connected", Toast.LENGTH_SHORT).show();
    }

然后需要调用此方法

public void onLocationChanged(android.location.Location location) {
        // Report to the UI that the location was updated
        String msg = "Updated Location: " +
                Double.toString(location.getLatitude()) + "," +
                Double.toString(location.getLongitude());
        if(tmp != location.getLatitude())
        {
            Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
        }
        tmp = location.getLatitude();
    }

您可以看到我在那里有 2 个 toast ，它们返回的实际 GPS 坐标很好，但是当我调用下面的代码时，它会在新的位置行 getLastKnownLocation

上崩溃

public String getLocation()
    {
        // Get the location manager
        LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
        Criteria criteria = new Criteria();
        String bestProvider = locationManager.getBestProvider(criteria, false);
        android.location.Location location = locationManager.getLastKnownLocation(bestProvider);
        Double lat,lon;
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Date date = new Date();
        try {
            lat = location.getLatitude ();
            lon = location.getLongitude ();
            Toast.makeText(this,""+lat.toString()+"-"+lon.toString(),Toast.LENGTH_SHORT).show();
            return new LatLng(lat, lon).toString();
        }
        catch (NullPointerException e){
            Toast.makeText(this,"HELL-NO",Toast.LENGTH_SHORT).show();
            Log.e("HELL-NO","n",e);
            e.printStackTrace();
            return null;
        }
    }

我只是不明白为什么当我尝试检索似乎已在 onLocationChanged 方法中检索到的位置时，它只是提供了一个空指针。

Answer 1

我只是改变了

locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER) to 
locationManager.getLastKnownLocation(LocationManager.PASSIVE_PROVIDER);

这为我解决了解决方案。完整 fragment :

map  = ((MapFragment) getFragmentManager().
            findFragmentById(R.id.map)).getMap();

    map.setMyLocationEnabled(true);

    locationManager = (LocationManager)getSystemService
            (Context.LOCATION_SERVICE); 
    getLastLocation = locationManager.getLastKnownLocation
            (LocationManager.PASSIVE_PROVIDER);
    currentLongitude = getLastLocation.getLongitude();
    currentLatitude = getLastLocation.getLatitude();

    currentLocation = new LatLng(currentLatitude, currentLongitude); 

希望这会有所帮助。