我是java和Android的新手。目前我正在做IOT项目，我必须自己学习Android Studio才能创建应用程序。我使用thingpeak作为云数据库，一切正常。我需要从我的GPS传感器绘制纬度和经度数据中的地图，并且我收到以下错误
java.lang.NullPointerException: Attempt to invoke virtual method 'double java.lang.Double.doubleValue()' on a null object reference
以下是我的代码。
public class Location extends FragmentActivity implements OnMapReadyCallback {
private GoogleMap mMap;
public static Double Latitude;
public static Double Longitude;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_location);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
//getLatitude method
private class getLatitude extends AsyncTask<String, String, String> {
String content = "";
@Override
protected void onPostExecute(String s) {
Latitude = Double.parseDouble(s);
}
@Override
protected void onProgressUpdate(String... values) {
}
@Override
protected String doInBackground(String... params) {
content = getContent();
return content;
}
private String getContent() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
HttpURLConnection urlConnection = null;
StringBuilder sb = new StringBuilder();
try {
URL url = new URL("https://api.thingspeak.com/channels/channel/fields/1/last?key=APIKey");
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String read;
while ((read = br.readLine()) != null) {
sb.append(read);
}
br.close();
} catch (Exception e) {
e.printStackTrace();
} finally {
urlConnection.disconnect();
}
return sb.toString();
}
}
//getLongitude method
private class getLongitude extends AsyncTask<String, String, String> {
String content = "";
@Override
protected void onPostExecute(String s) {
Longitude = Double.parseDouble(s);
}
@Override
protected void onProgressUpdate(String... values) {
}
@Override
protected String doInBackground(String... params) {
content = getContent();
return content;
}
private String getContent() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
HttpURLConnection urlConnection = null;
StringBuilder sb = new StringBuilder();
try {
URL url = new URL("https://api.thingspeak.com/channels/channel/fields/2/last?key=APIKey");
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String read;
while ((read = br.readLine()) != null) {
sb.append(read);
}
br.close();
} catch (Exception e) {
e.printStackTrace();
} finally {
urlConnection.disconnect();
}
return sb.toString();
}
}
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
new getLatitude().execute("ddd", "fdf", "dfdf");
new getLongitude().execute("ddd", "fdf", "dfdf");
// Add a marker and move the camera
LatLng location = new LatLng(Latitude,Longitude);
mMap.addMarker(new MarkerOptions().position(location).title("Device Location Marker"));
mMap.moveCamera(CameraUpdateFactory.newLatLng(location));
}
}