Question

我正在尝试使用可检测GPS是否启用的应用。如果没有，应用程序必须使用启用GPS时收到的数据更新位置数据，但现在我无法这样做。我的代码如下：

public class App extends Activity implements LocationListener {
private GoogleMap googleMap;
protected TextView city;
protected TextView street;
LocationManager lm = null;
LocationListener ll = null; 
Location location;
Boolean isGPSEnabled;
Boolean isNetworkEnabled;
Boolean canGetLocation;
double longitude;
double latitude;
public static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters
public static final long MIN_TIME_BW_UPDATES = 1000*60*1; // 1 minute

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

    boolean flag = displayGpsStatus();

    if (flag){
        initilizeMap();

        lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 

        location = getLocation();
        longitude = location.getLongitude();
        latitude = location.getLatitude();

        Geocoder geocoder;
        List<Address> addresses;
        String ciudad="",calle="";
        try{
            geocoder = new Geocoder(this, Locale.getDefault());
            addresses = geocoder.getFromLocation(latitude, longitude, 1);

            calle = addresses.get(0).getAddressLine(0);
            ciudad = addresses.get(0).getLocality();
        }
        catch(IOException ex)
        {
            System.out.println(ex);
        }


        city = (TextView)findViewById(R.id.txtCiudad);
        street = (TextView)findViewById(R.id.txtCalle);
        city.setText(ciudad);
        street.setText(calle);


        // create marker
        MarkerOptions marker = new MarkerOptions().position(new LatLng(latitude, longitude)).title("Hello Maps ");
        marker.icon(BitmapDescriptorFactory.fromResource(R.drawable.car_map_35_35));

        // adding marker
        googleMap.addMarker(marker);

        CameraPosition cameraPosition = new CameraPosition.Builder().target(
                new LatLng(latitude, longitude)).zoom(17).build();

        googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
    }
    else
    {
        alertbox("Estado GPS", "Su GPS está desactivado");
    }
}

@Override
public void onLocationChanged(Location location) {
    boolean flag = displayGpsStatus();

    if (flag){

        initilizeMap();

        lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 
        location = getLocation();
        double longitude = location.getLongitude();
        double latitude = location.getLatitude();

        Geocoder geocoder;
        List<Address> addresses;
        String ciudad="",calle="";
        try{
            geocoder = new Geocoder(this, Locale.getDefault());
            addresses = geocoder.getFromLocation(latitude, longitude, 1);

            calle = addresses.get(0).getAddressLine(0);
            ciudad = addresses.get(0).getLocality();
        }
        catch(IOException ex)
        {
            System.out.println(ex);
        }


        city = (TextView)findViewById(R.id.txtCiudad);
        street = (TextView)findViewById(R.id.txtCalle);
        city.setText(ciudad);
        street.setText(calle);


        // create marker
        MarkerOptions marker = new MarkerOptions().position(new LatLng(latitude, longitude)).title("Hello Maps ");
        marker.icon(BitmapDescriptorFactory.fromResource(R.drawable.car_map_35_35));

        // adding marker
        googleMap.addMarker(marker);

        CameraPosition cameraPosition = new CameraPosition.Builder().target(
                new LatLng(latitude, longitude)).zoom(17).build();

        googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
    }
    else
    {
        alertbox("Estado GPS", "Su GPS está desactivado");
    }
}

protected void alertbox(String title, String mymessage) {  
  AlertDialog.Builder builder = new AlertDialog.Builder(this);  
  builder.setMessage(mymessage)  
  .setCancelable(false)  
  .setTitle(title)  
  .setPositiveButton("Habilitar GPS",  
   new DialogInterface.OnClickListener() {  
   public void onClick(DialogInterface dialog, int id) {  
        Intent myIntent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);  
        startActivity(myIntent);  
        dialog.cancel();  
   }  
   })  
   .setNegativeButton("Cancelar",  
   new DialogInterface.OnClickListener() {  
   public void onClick(DialogInterface dialog, int id) {  
    // cancel the dialog box  
    dialog.cancel();  
    }  
   });  
  AlertDialog alert = builder.create();  
  alert.show();  
 } 

public Location getLocation() {
    try {
        lm = (LocationManager) this
                .getSystemService(LOCATION_SERVICE);

        // getting GPS status
        isGPSEnabled = lm
                .isProviderEnabled(LocationManager.GPS_PROVIDER);

        // getting network status
        isNetworkEnabled = lm
                .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

        if (!isGPSEnabled && !isNetworkEnabled) {
            // no network provider is enabled
        } else {
            this.canGetLocation = true;
            if (isNetworkEnabled) {
                lm.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        MIN_TIME_BW_UPDATES,
                        MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                Log.d("Network", "Network Enabled");
                if (lm != null) {
                    location = lm
                            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    if (location != null) {
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }
            // if GPS Enabled get lat/long using GPS Services
            if (isGPSEnabled) {
                if (location == null) {
                    lm.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("GPS", "GPS Enabled");
                    if (lm != null) {
                        location = lm
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
            }
        }

    } catch (Exception e) {
        e.printStackTrace();
    }

    return location;
}

private void initilizeMap() {
    if (googleMap == null) {
        googleMap = ((MapFragment) getFragmentManager().findFragmentById(
                R.id.map)).getMap();

        // check if map is created successfully or not
        if (googleMap == null) {
            Toast.makeText(getApplicationContext(),
                    "No se ha podido mostrar el mapa", Toast.LENGTH_SHORT)
                    .show();
        }
    }
}

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    ll = new App();
    lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
    lm.requestSingleUpdate(LocationManager.GPS_PROVIDER, ll, null);
    super.onResume();

}

@Override
  protected void onPause() {
    super.onPause();
    lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
    lm.removeUpdates(ll); 
    lm = null;
  }

现在，如果GPS已禁用，然后我启用它，则显示的数据为空。如何在启用GPS后更新数据？

先谢谢你。

在onResume方法中输入相同的onCreate方法代码后更新代码：

10-27 10：08：16.578：E / AndroidRuntime（30986）：java.lang.RuntimeException：无法恢复活动{com.axiomapps.app/com.axiomapps.app.app}：java.lang.NullPointerException 10-27 10:08：16.578：E / AndroidRuntime（30986）：在android.app.ActivityThread.performResumeActivity（ActivityThread.java:2919） 10-27 10:08：16.578：E / AndroidRuntime（30986）：在android.app.ActivityThread.handleResumeActivity（ActivityThread.java:2948） 10-27 10:08：16.578：E / AndroidRuntime（30986）：在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1358） 10-27 10：08：16.578：E / AndroidRuntime（30986）：在android.os.Handler.dispatchMessage（Handler.java:99） 10-27 10:08：16.578：E / AndroidRuntime（30986）：在android.os.Looper.loop（Looper.java:176） 10-27 10:08：16.578：E / AndroidRuntime（30986）：在android.app.ActivityThread.main（ActivityThread.java:5419） 10-27 10：08：16.578：E / AndroidRuntime（30986）：at java.lang.reflect.Method.invokeNative（Native Method） 10-27 10：08：16.578：E / AndroidRuntime（30986）：at java.lang.reflect.Method.invoke（Method.java:525） 10-27 10：08：16.578：E / AndroidRuntime（30986）：at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1046） 10-27 10:08：16.578：E / AndroidRuntime（30986）：at com.android.internal.os.ZygoteInit.main（ZygoteInit.java:862） 10-27 10:08：16.578：E / AndroidRuntime（30986）：at dalvik.system.NativeStart.main（Native Method） 10-27 10:08：16.578：E / AndroidRuntime（30986）：引起：java.lang.NullPointerException 10-27 10：08：16.578：E / AndroidRuntime（30986）：at com.axiomapps.app.App.onResume（App.java:249） 10-27 10:08：16.578：E / AndroidRuntime（30986）：在android.app.Instrumentation.callActivityOnResume（Instrumentation.java:1209） 10-27 10:08：16.578：E / AndroidRuntime（30986）：在android.app.Activity.performResume（Activity.java:5450） 10-27 10：08：16.578：E / AndroidRuntime（30986）：在android.app.ActivityThread.performResumeActivity（ActivityThread.java:2909） 10-27 10:08：16.578：E / AndroidRuntime（30986）：... 10 more

Answer 1

您创建活动的新对象，这是错误的。你不能这样做：

ll = new App(); // you created new instance of your activity, you can't do that
lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
lm.requestSingleUpdate(LocationManager.GPS_PROVIDER, ll, null);

必须这样做：

lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
lm.requestSingleUpdate(LocationManager.GPS_PROVIDER, this, null); //replaced to "this"

启用GPS后更新位置数据

1 个答案: