我一直在 Android Studio 中使用 Java 来开发基于 map 的 Android 应用程序来进行查找，并且我一直在尝试在 map 上的两个标记之间创建折线一段时间，但这个 NullPointerException 一直显示:
java.lang.NullPointerException: Attempt to read from field 'double com.google.android.gms.maps.model.LatLng.latitude' on a null object reference
at com.example.waynedeng.mapx.Home.MapsActivity.getRequestUrl(MapsActivity.java:267)
at com.example.waynedeng.mapx.Home.MapsActivity.polylineSetup(MapsActivity.java:261)
at com.example.waynedeng.mapx.Home.MapsActivity.onMapReady(MapsActivity.java:180)
at com.google.android.gms.maps.zzaj.zza(Unknown Source:7)
at com.google.android.gms.maps.internal.zzaq.onTransact(Unknown Source:18)
at android.os.Binder.transact(Binder.java:627)
at fg.b(:com.google.android.gms.dynamite_mapsdynamite@13280052@13.2.80 (040700-211705629):19)
at com.google.android.gms.maps.internal.bg.a(:com.google.android.gms.dynamite_mapsdynamite@13280052@13.2.80 (040700-211705629):5)
at com.google.maps.api.android.lib6.impl.be.run(:com.google.android.gms.dynamite_mapsdynamite@13280052@13.2.80 (040700-211705629):5)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
以下是我的声明:
private GoogleMap mMap;
private Location lastKnownLocation;
private FusedLocationProviderClient client;
private ArrayList<LatLng> points;
private Handler handler;
private LatLng you = getLatLng(), destination = new LatLng(37.727812, -122.405864);
private LocationManager locationManager;
private List<Address> addresses;
private Geocoder geocoder;
private MarkerOptions youMarkerO, destinationMarkerO;
private Marker youMarker, destinationMarker;
错误位置似乎是在getDirections()方法中:
private String getDirections(String reqUrl) throws IOException {
String response = "";
InputStream inputStream = null;
HttpURLConnection con = null;
try {
URL url = new URL(reqUrl);
con = (HttpURLConnection) url.openConnection();
con.connect();
inputStream = con.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
StringBuffer stringBuffer = new StringBuffer();
String line = ""; //ERROR
while((line = bufferedReader.readLine()) != null){
stringBuffer.append(line);
}
response = stringBuffer.toString();
inputStreamReader.close();
bufferedReader.close();
} catch (Exception e) {
e.printStackTrace();
}
finally {
if(inputStream !=null){
inputStream.close();
}
con.disconnect();
}
return response;
}
并在重写的 onLocationChanged() 方法中:
locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
locationListener = new LocationListener() {
//Update location
@Override
public void onLocationChanged(Location location) {
saveInfo();
lastKnownLocation = location;
Log.d(TAG, location.toString());
Log.d(TAG, "Map cleared");
mMap.clear();
you = new LatLng(location.getLatitude(), location.getLongitude());
mMap.getUiSettings().setZoomControlsEnabled(true);
mMap.addMarker(youMarkerO);
moveCamera(you, 0.5f);
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
};
这是我的 getRequestUrl() 方法:
private String getRequestUrl(LatLng one, LatLng two){
if( one != null && two != null){
String origin = "origin="+ one.latitude + "," + one.longitude;
String dest = "destination="+ two.latitude + "," + two.longitude;
String sensor = "sensor=false";
String mode = "mode=driving";
String param = origin + "&" + dest + "&" + sensor + "&" + mode;
String output = "json";
String baseUrl = "https://maps.googleapis.com/maps/api/directions/";
String requestUrl = baseUrl + output + "?" + param;
return requestUrl;
}
return null;
}
起初，我以为这是因为我在初始化之前在 polylineSetup() 中访问了“you”和“destination”，但我更改了它，但它仍然不起作用。我试图解决它并阅读这个问题:What is a NullPointerException, and how do I fix it?但这并没有涵盖问题。任何信息或修复都会有帮助。谢谢:)
最佳答案
排队前检查
if( pickup.latitude != null && pickup.longitude != null && destination.latitude != null && destination.longitude != null)
关于java - NullPointerException - 尝试从空对象引用上的字段纬度读取，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/52378773/