我有一个AsyncTask已添加到我的 android 应用程序上的 Web 服务调用中。当我在调试模式下单步执行代码时，我没有在调用的变量上获得空指针，evacRoute但是当我通过播放运行它时，我在if (!evacRoute.getLatLngs().isEmpty())下面的 locationlistener 上得到一个空指针异常：
/**
*Mylocationlistener class will give the current GPS location
*with the help of Location Listener interface
*/
private class PointLocationListener implements LocationListener {
private boolean zoomed = false;
@Override
public void onLocationChanged(Location location) {
if (location != null) {
// ---Get current location latitude, longitude---
Log.d("LOCATION CHANGED", location.getLatitude() + "");
Log.d("LOCATION CHANGED", location.getLongitude() + "");
latitude = 36.857648;
longitude = -76.170959;
currentLocation = new LatLng(latitude, longitude);
//currentLatLng = new LatLng(latitude, longitude);
Marker currentLocationMarker = map.addMarker(new MarkerOptions().position(currentLocation).title("Current Location"));
// Move the camera instantly to current location with a zoom of 15.
map.moveCamera(CameraUpdateFactory.newLatLngZoom(currentLocation, 15));
// Zoom in, animating the camera.
if (evacName != null){
String latStr = String.valueOf(latitude);
String longStr = String.valueOf(longitude);
AsyncRoute asyncRoute = new AsyncRoute(evacName, currentLocation, latStr, longStr);
asyncRoute.execute();
System.out.println();
}
if (!zoomed) {
map.animateCamera(CameraUpdateFactory.zoomTo(12), 2000, null);
zoomed = true;
}
if (!firstPass){
currentLocationMarker.remove();
}
firstPass = false;
Toast.makeText(MapViewActivity.this,"Latitude = "+
latitude + "" +"Longitude = "+ longitude,
Toast.LENGTH_LONG).show();
evacRoute = DALController.sharedInstance().getSelectedEvacRoute();
if (fuelStopBundle != null){
String shelorfuelAddress = fuelStopBundle.getString("key");
String type = fuelStopBundle.getString("type");
String evacStr = fuelStopBundle.getString("evacObject");
if (shelorfuelAddress != "" && shelorfuelAddress != null && type.equals("fuelstop")){
try {
ShowFuelStopAndRoute(shelorfuelAddress);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} else if (shelorfuelAddress != "" && shelorfuelAddress != null && type.equals("shelter")){
try {
ShowShelterAndRoute(shelorfuelAddress);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} else if (evacStr != null && evacRoute != null){
if (!evacRoute.getLatLngs().isEmpty()){
showEvacuationRoute(evacRoute);
}
}
} else {
}
} else {
}
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
}
这是我的异步任务：
public class AsyncRoute extends AsyncTask<Void, Void, EvacRoute > {
public String routeName;
public LatLng currentLocation;
public String lat;
public String lon;
public AsyncRoute (String routeName, LatLng currentLocation, String lat, String lon){
this.routeName = routeName;
this.currentLocation = currentLocation;
this.lat = lat;
this.lon = lon;
}
@Override
protected EvacRoute doInBackground(Void... params) {
try {
return DALController.sharedInstance().getEvacuationRoute(routeName, currentLocation, lat, lon);
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (URISyntaxException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SAXException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(EvacRoute result) {
// Function finished and value has returned.
}
}
这是在上面的 AsyncTask 方法中调用的方法：
public EvacRoute getEvacuationRoute(String routeName, LatLng currentLocation, String lat, String lon) throws URISyntaxException, ClientProtocolException, IOException, ParserConfigurationException, SAXException{
evacRouteList = new ArrayList<EvacRoute>();
evacRoute = new EvacRoute();
evacRoute.setDestinationName(routeName);
BufferedReader in = null;
String page;
latslngsList = new ArrayList<LatLng>();
try {
latslngsList.add(currentLocation);
HttpClient client = new DefaultHttpClient();
HttpPost request = new HttpPost();
request.setURI(new URI("http://heed-dev01.vmasc.odu.edu:53556/heed_service2.asmx/get_route_info_from_lat_lon"));
//Add The parameters. The asmx webservice requires a double but gets posted as a string in a text field
List<NameValuePair> nameValPairs = new ArrayList<NameValuePair>(2);
nameValPairs.add(new BasicNameValuePair("Route_Name", routeName));
nameValPairs.add(new BasicNameValuePair("In_Lat", lat));
nameValPairs.add(new BasicNameValuePair("In_Lon", lon));
request.setEntity(new UrlEncodedFormEntity(nameValPairs));
HttpResponse response = client.execute(request);
in = new BufferedReader
(new InputStreamReader(response.getEntity().getContent()));
StringBuffer sb = new StringBuffer("");
String line = "";
String NL = System.getProperty("line.separator");
while ((line = in.readLine()) != null) {
sb.append(line + NL);
}
in.close();
page = sb.toString();
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document doc = db.parse(new InputSource(new StringReader(page)));
// normalize the document
doc.getDocumentElement().normalize();
// get the root node
NodeList nodeList = doc.getElementsByTagName("simple_ll_waypoint");
double latitude = 0;
double longitude= 0;
// the node has three child nodes
for (int n = 0; n < nodeList.getLength(); n++) {
String latString = "";
String longString = "";
Node node=nodeList.item(n);
String upperNode = node.getNodeName();
StringBuilder addressStrBlder = new StringBuilder();
for (int i = 0; i < node.getChildNodes().getLength(); i++) {
Node temp=node.getChildNodes().item(i);
String nodeName = temp.getNodeName();
String nodevalue = temp.getNodeValue();
if(temp.getNodeName().equalsIgnoreCase("Lat")){
latString = temp.getTextContent();
latitude = Double.parseDouble(latString);
} else if(temp.getNodeName().equalsIgnoreCase("Lon")){
longString = temp.getTextContent();
longitude = Double.parseDouble(longString);
LatLng latlng = new LatLng(latitude, longitude);
latslngsList.add(latlng);
}
}
//Log.e("Fuel Stop", fuelStop.toString());
}
//System.out.println(page);
} catch (Exception E) {
E.printStackTrace();
}
finally {
if (in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
evacRoute.setLatLngList(latslngsList);
evacRouteList.add(evacRoute);
return evacRoute;
}
这是堆栈跟踪：
05-16 09:48:31.917: E/AndroidRuntime(3649): FATAL EXCEPTION: main
05-16 09:48:31.917: E/AndroidRuntime(3649): java.lang.NullPointerException
05-16 09:48:31.917: E/AndroidRuntime(3649): at com.eema.MapViewActivity$PointLocationListener.onLocationChanged(MapViewActivity.java:499)
05-16 09:48:31.917: E/AndroidRuntime(3649): at android.location.LocationManager$ListenerTransport._handleMessage(LocationManager.java:255)
05-16 09:48:31.917: E/AndroidRuntime(3649): at android.location.LocationManager$ListenerTransport.access$000(LocationManager.java:184)
05-16 09:48:31.917: E/AndroidRuntime(3649): at android.location.LocationManager$ListenerTransport$1.handleMessage(LocationManager.java:200)
05-16 09:48:31.917: E/AndroidRuntime(3649): at android.os.Handler.dispatchMessage(Handler.java:99)
05-16 09:48:31.917: E/AndroidRuntime(3649): at android.os.Looper.loop(Looper.java:137)
05-16 09:48:31.917: E/AndroidRuntime(3649): at android.app.ActivityThread.main(ActivityThread.java:5041)
05-16 09:48:31.917: E/AndroidRuntime(3649): at java.lang.reflect.Method.invokeNative(Native Method)
05-16 09:48:31.917: E/AndroidRuntime(3649): at java.lang.reflect.Method.invoke(Method.java:511)
05-16 09:48:31.917: E/AndroidRuntime(3649): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-16 09:48:31.917: E/AndroidRuntime(3649): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-16 09:48:31.917: E/AndroidRuntime(3649): at dalvik.system.NativeStart.main(Native Method)
我收到错误的 mapview 活动的第 499 行if (!evacRoute.getLatLngs().isEmpty()){位于 PointLocationListener 的上述代码中，因为 evacRoute.getLatsLngs() 为空。我可以将一些代码移动到 onPostExecute 中吗？如果可以，如何？