GPS位置仅返回null（0.0,0.0）

我有一个适用于Android设备的应用程序，具有多个地址。通过单击任何想要获取用户的当前位置的地址，并在Google地图（http://maps.google.com/maps?&saddr =“）上播放链接以及目的地的坐标。

但是，出现的“纬度”和“经度”结果仅返回“ 0.0”。

谁能帮我？

对不起，英语不好。

public class Guaruja extends Activity Activity implements LocationListener {

Button bttela2;
TextView t1;
Uri uri;
    protected LocationManager locationManager;
    protected LocationListener locationListener;
    protected Context context;
String provider;



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

    t1 = (TextView) findViewById(R.id.t1);


    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);

    TextView1 = (TextView) findViewById (R.id.TextView1);


    TextView1.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            String lati = String.valueOf(latitude);
            String longi = String.valueOf(longitude);
            String firt = "http://maps.google.com/maps?&saddr=";
            String secord="&daddr=-22.748085, -47.369444";
            String virgula=",";
            String url= firt+latitude+virgula+longitude+secord;
            uri=Uri.parse(url);
            Intent intent = new Intent(Intent.ACTION_VIEW, uri);
            startActivity(intent);

        }


    });


}


public void onLocationChanged(Location location){

       latitude = location.getLatitude() * 1E6;
       longitude = location.getLongitude() * 1E6;

    }

   public void onProviderDisabled(String provider) {
    Log.d("Latitude","disable");
}


public void onProviderEnabled(String provider) {
    Log.d("Latitude","enable");
}


public void onStatusChanged(String provider, int status, Bundle extras) {
    Log.d("Latitude","status");
}

权限：

    <uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>