问题描述
public class MapsActivity extends FragmentActivity implements LocationListener{
GoogleMap mGoogleMap;
Spinner mSprPlaceType;
String[] mPlaceType=null;
String[] mPlaceTypeName=null;
double mLatitude=0;
double mLongitude=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
// Array of place types
mPlaceType = getResources().getStringArray(R.array.place_type);
// Array of place type names
mPlaceTypeName = getResources().getStringArray(R.array.place_type_name);
// Creating an array adapter with an array of Place types
// to populate the spinner
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, mPlaceTypeName);
// Getting reference to the Spinner
mSprPlaceType = (Spinner) findViewById(R.id.spr_place_type);
// Setting adapter on Spinner to set place types
mSprPlaceType.setAdapter(adapter);
Button btnFind;
// Getting reference to Find Button
btnFind = ( Button ) findViewById(R.id.btn_find);
// Getting Google Play availability status
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());
if(status!=ConnectionResult.SUCCESS){ // Google Play Services are not available
int requestCode = 10;
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
dialog.show();
}
else
{ // Google Play Services are available
// Getting reference to the SupportMapFragment
SupportMapFragment fragment = ( SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
// Getting Google Map
mGoogleMap = fragment.getMap();
// Enabling MyLocation in Google Map
mGoogleMap.setMyLocationEnabled(true);
// Getting LocationManager object from System Service LOCATION_SERVICE
LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
// Creating a criteria object to retrieve provider
Criteria criteria = new Criteria();
// Getting the name of the best provider
String provider = locationManager.getBestProvider(criteria, true);
// Getting Current Location From GPS
Location location = locationManager.getLastKnownLocation(provider);
if(location!=null){
onLocationChanged(location);
}
locationManager.requestLocationUpdates(provider, 20000, 0, this);
// Setting click event lister for the find button
btnFind.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int selectedPosition = mSprPlaceType.getSelectedItemPosition();
String place = mPlaceTypeName[selectedPosition];
Toast.makeText(getApplicationContext(),"working",Toast.LENGTH_LONG).show();
StringBuilder sb = new StringBuilder("https://maps.googleapis.com/maps/api/place/nearbysearch/json?");
sb.append("types=place");
sb.append("&location="+mLatitude+", "+mLongitude);
sb.append("&radius=10000");
sb.append("&sensor=true");
sb.append("&key=[My API Key]");
// Creating a new non-ui thread task to download json data
PlacesTask placesTask = new PlacesTask();
// Invokes the "doInBackground()" method of the class PlaceTask
placesTask.execute(sb.toString());
Toast.makeText(getApplicationContext(),"working",Toast.LENGTH_LONG).show();
}
});
}
}
/** A method to download json data from url */
private String downloadUrl(String strUrl) throws IOException{
String data = "";
InputStream iStream = null;
HttpURLConnection urlConnection = null;
try{
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while( ( line = br.readLine()) != null){
sb.append(line);
}
data = sb.toString();
br.close();
}catch(Exception e){
Log.d("Exception while downloading url", e.toString());
}finally{
iStream.close();
urlConnection.disconnect();
}
return data;
}
/** A class, to download Google Places */
private class PlacesTask extends AsyncTask<String, Integer, String>{
String data = null;
// Invoked by execute() method of this object
@Override
protected String doInBackground(String... url) {
try{
data = downloadUrl(url[0]);
}catch(Exception e){
Log.d("Background Task",e.toString());
}
return data;
}
// Executed after the complete execution of doInBackground() method
@Override
protected void onPostExecute(String result){
ParserTask parserTask = new ParserTask();
// Start parsing the Google places in JSON format
// Invokes the "doInBackground()" method of the class ParseTask
parserTask.execute(result);
}
}
/** A class to parse the Google Places in JSON format */
private class ParserTask extends AsyncTask<String, Integer, List<HashMap<String,String>>>{
JSONObject jObject;
// Invoked by execute() method of this object
@Override
protected List<HashMap<String,String>> doInBackground(String... jsonData) {
List<HashMap<String, String>> places = null;
PlaceJSONParser placeJsonParser = new PlaceJSONParser();
try{
jObject = new JSONObject(jsonData[0]);
/** Getting the parsed data as a List construct */
places = placeJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
return places;
}
// Executed after the complete execution of doInBackground() method
@Override
protected void onPostExecute(List<HashMap<String,String>> list){
// Clears all the existing markers
mGoogleMap.clear();
for(int i=0;i<list.size();i++){
// Creating a marker
MarkerOptions markerOptions = new MarkerOptions();
// Getting a place from the places list
HashMap<String, String> hmPlace = list.get(i);
// Getting latitude of the place
double lat = Double.parseDouble(hmPlace.get("lat"));
// Getting longitude of the place
double lng = Double.parseDouble(hmPlace.get("lng"));
// Getting name
String name = hmPlace.get("place_name");
// Getting vicinity
String vicinity = hmPlace.get("vicinity");
LatLng latLng = new LatLng(lat, lng);
// Setting the position for the marker
markerOptions.position(latLng);
// Setting the title for the marker.
//This will be displayed on taping the marker
markerOptions.title(name + " : " + vicinity);
// Placing a marker on the touched position
mGoogleMap.addMarker(markerOptions);
}
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
@Override
public void onLocationChanged(Location location) {
mLatitude = location.getLatitude();
mLongitude = location.getLongitude();
LatLng latLng = new LatLng(mLatitude, mLongitude);
mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(12));
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
}
Log:
08-19 14:52:02.145 22460-22460/com.example.admin.newmapplace E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: com.example.admin.newmapplace, PID: 22460 java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference at com.example.admin.newmapplace.MapsActivity$ParserTask.onPostExecute(MapsActivity.java:245) at com.example.admin.newmapplace.MapsActivity$ParserTask.onPostExecute(MapsActivity.java:215) at android.os.AsyncTask.finish(AsyncTask.java:636) at android.os.AsyncTask.access$500(AsyncTask.java:177) at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:653) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5254) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
The error is quite explanatory:
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at com.example.admin.newmapplace.MapsActivity$ParserTask.onPostExecute(MapsActivity.java:245)
at com.example.admin.newmapplace.MapsActivity$ParserTask.onPostExecute(MapsActivity.java:215)
If you check in the ParserTask onPostExecute, that line (215 or 245) should be:
for(int i=0;i<list.size();i++){
And the issue is that, that method receives a null "list" item, which is taken from the method parameter:
protected void onPostExecute(List<HashMap<String,String>> list){
It is null because your "doInBackground" method returns a null object, looking at your code:
@Override
protected List<HashMap<String,String>> doInBackground(String... jsonData) {
List<HashMap<String, String>> places = null;
PlaceJSONParser placeJsonParser = new PlaceJSONParser();
try{
jObject = new JSONObject(jsonData[0]);
/** Getting the parsed data as a List construct */
places = placeJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
return places;
}
It seems that an exception is raised and then "places" is not set, leading to a null object returned. If you check the log (you set Debug, it's better to do Log.e in this cases), you should se a line with "Exception" and the text of the exception.An alternative for logging exception:
Log.e(TAGOFMESSAGE,"Raised an exception during doInBackground Method",e);
This will log an error and will put the stack trace of the exception in the log, helping you understanding what raised the exception.
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