LocationManager 抛出 NullPointerExpection [英] LocationManager throws NullPointerExpection

问题描述

请我有这段代码一直在为我工作，突然间它不再工作了，它在

Please I have this code which has been working for me all this while, all of a sudden it is not working any more, it returns null pointer exception at

double lat = (double) (lastKnownLocation.getLatitude());.

我已在清单文件中设置了所有必需的权限，但似乎无法再次运行.我认为现在使用 GPS 提供商肯定有问题.

I have set all required permission at the manifest file , but it seems not to work again. I think there must be a problem using the GPS provider now.

    latituteField = (TextView) findViewById(R.id.TextViewLatitudeValue);
    longitudeField = (TextView) findViewById(R.id.TextViewLongitudeValue);
    SpeedField = (TextView) findViewById(R.id.textViewSpeedValue);
    AltitudeField = (TextView) findViewById(R.id.textViewAltitudeValue);        
    AddressLabel=(TextView)findViewById(R.id.textViewAddress);
    lbllatitude=(TextView)findViewById(R.id.lblLatDMS);
    lbllongitude=(TextView)findViewById(R.id.lblLongDMS);



    // Get the location manager
    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    // GPS_PROVIDER
    String locationProvider = LocationManager.GPS_PROVIDER;  
    Location lastKnownLocation = locationManager.getLastKnownLocation(locationProvider);

    LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
    boolean enabled = service.isProviderEnabled(LocationManager.GPS_PROVIDER);

    // check if enabled and if not send user to the GSP settings
    // Better solution would be to display a dialog and suggesting to 
    // go to the settings
    if (!enabled) 
    {           
      Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
      startActivity(intent);

    }
    else if (locationProvider!= null) 
    {
     Toast.makeText(this, locationProvider +" has been selected",Toast.LENGTH_SHORT).show();
      onLocationChanged(lastKnownLocation);
    } 
    else 
    {
      latituteField.setText("0.00");
      longitudeField.setText("0.00");
      AltitudeField.setText("0.00");
      SpeedField.setText("0.00");

    }

  }

  /* Request updates at startup */
  @Override
  protected void onResume() {
    super.onResume();
    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 400, 1, this);
  }

  /* Remove the locationlistener updates when Activity is paused */
  @Override
  protected void onPause() {
    super.onPause();
    locationManager.removeUpdates(this);
  }

  @Override
  public void onLocationChanged(Location lastKnownLocation) {

    double lat = (double) (lastKnownLocation.getLatitude());
    double lng = (double) (lastKnownLocation.getLongitude());
    double Alt = (double) (lastKnownLocation.getAltitude());
    double Speed = (double) (lastKnownLocation.getSpeed());

    latituteField.setText(String.format("%.5f",lat));
    longitudeField.setText(String.format("%.5f",lng));
    AltitudeField.setText(String.format("%.5f",Alt));
    SpeedField.setText(String.format("%.5f",Speed));

推荐答案

LastKnownLocation 如果它的位置太旧或提供程序从未打开，将返回 null.您必须考虑到这一点.确保获得有效位置的唯一方法是请求更新并在 onLocationChanged 中获取它.

LastKnownLocation will return null if either the location it has is too old or if the provider has never been turned on. You must take this into account. THe only way to be sure to get a valid location is to request updates and get it in onLocationChanged.

此外，lastKnownLocation 可能会返回一个非常错误的值 - 10 或 15 分钟前的值是可能的.您可以使用它，但不要期望准确.

ALso, lastKnownLocation may return a value that's very wrong- something from 10 or 15 minutes ago is possible. You can use it, but don't expect accuracy.

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