使用GPS時谷歌地圖活動崩潰

Question

我搜索了這個問題的答案近2個小時，但是我沒有找到解決辦法。事情是我想要使用設備GPS創建Google地圖活動，並且如果它關閉，請要求用戶激活它。我面臨的問題是每次我想打開活動時都會崩潰。我正在測試一個真實的設備。

這裏是我的代碼：

private GoogleMap mMap; // Might be null if Google Play services APK is not available. 
    public double latitude; 
    public double longitude; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_pantalla_hospitales_farmacias_cerca); 
     setUpMapIfNeeded(); 

    } 

    @Override 
    protected void onResume() { 
     super.onResume(); 
     setUpMapIfNeeded(); 
    } 

    private void setUpMapIfNeeded() { 
     // Do a null check to confirm that we have not already instantiated the map. 
     if (mMap == null) { 
      // Try to obtain the map from the SupportMapFragment. 
      mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)) 
        .getMap(); 
      // Check if we were successful in obtaining the map. 
      if (mMap != null) { 
       setUpMap(); 
      } 
     } 
    } 

    private void setUpMap() { 

     // Enable MyLocation Layer of Google Map 
     mMap.setMyLocationEnabled(true); 

     // Create a criteria object to retrieve provider 
     Criteria criteria = new Criteria(); 

     // // Get LocationManager object from System Service LOCATION_SERVICE 
     LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 
     if (!locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) buildAlertMessageNoGps(); 

     // Get the name of the best provider 
     locationManager.getBestProvider(criteria, true); 

     // Get Current Location 
     Location myLocation = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER); 

     // set map type 
     mMap.setMapType(GoogleMap.MAP_TYPE_HYBRID); 

     // Get latitude of the current location 
     latitude = myLocation.getLatitude(); 

     // Get longitude of the current location 
     longitude = myLocation.getLongitude(); 

     // Create a LatLng object for the current location 
     LatLng latLng = new LatLng(latitude, longitude); 

     // Show the current location in Google Map 
     mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng)); 

     // Zoom in the Google Map 
     mMap.animateCamera(CameraUpdateFactory.zoomTo(14)); 
     mMap.addMarker(new MarkerOptions().position(new LatLng(latitude, longitude)).title("Estás aquí").snippet("Farmacias y hospitales cercanos")); 

     // request that the provider send this activity GPS updates every 20 seconds 
     //locationManager.requestLocationUpdates(provider, 20000, 0, this); 

    } 

    @Override 
    public void onLocationChanged(Location location) { 
     mMap.clear(); 
     longitude = location.getLongitude(); 
     latitude = location.getLatitude(); 
    } 

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

    } 

    @Override 
    public void onProviderEnabled(String provider) { 

    } 

    @Override 
    public void onProviderDisabled(String provider) { 

    } 

    // function that opened an activity to turn on the GPS 
    private void buildAlertMessageNoGps() { 
     final AlertDialog.Builder builder = new AlertDialog.Builder(this); 
     builder.setMessage("El GPS está desactivado. ¿Quiere activarlo? ") 
       .setCancelable(true) 
       .setPositiveButton("Sí.", 
         new DialogInterface.OnClickListener() { 
          public void onClick(final DialogInterface dialog, final int id) { 
           startActivity(new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS)); 
          } 
         }) 
       .setNegativeButton("No", new DialogInterface.OnClickListener() { 
        public void onClick(final DialogInterface dialog, final int id) { 
         dialog.cancel(); 
         PantallaHospitalesFarmaciasCerca.this.finish(); 
        } 
       }); 
     final AlertDialog alert = builder.create(); 
     alert.show(); 
    } 


} 

的事情是，如果我使用：

String provider = locationManager.getBestProvider(criteria, true); 
Location myLocation = locationManager.getLastKnownLocation(provider); 

什麼，而不是我用它工作的時刻，但不與GPS，它的工作原理網絡位置。我怎樣才能使它與GPS一起工作？ 非常感謝。

Answer 1

當你調用getLastKnownLocation，有可能的結果是空：

如果提供的是當前被禁用，則返回null。

當您檢查

if (!locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) buildAlertMessageNoGps(); 

的代碼塊仍然被執行後，所以getLastKnownLocation仍稱，而GPS是禁用的。考慮使用一個else塊來防止這種情況。