问题
Possible Duplicate:
android.os.NetworkOnMainThreadException
i am fetching JSON data into MapView to show locations, but whenever i run my program not getting data into Map just getting blank map without json data, here i am placing my json data and Activity Code, please tell me where i am doing mistake { "maps": [ {
"title": "Place One",
"latitude" : "46.483742",
"longitude" : "7.663157",
"country": "Switzerland"
},
{
"title" : "Place Two",
"latitude" : "59.25235",
"longitude" : "18.465536",
"country" : "Sweden"
},
{
"title" : "Place Three",
"latitude" : "56.404182",
"longitude" : "-3.818855",
"country" : "Scotland"
}
]
}
Activity Code:-
public class Main extends MapActivity {
public GeoPoint point;
TapControlledMapView mapView; // use the custom TapControlledMapView
List<Overlay> mapOverlays;
Drawable drawable;
SimpleItemizedOverlay itemizedOverlay;
@Override
public void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mapView = (TapControlledMapView) findViewById(R.id.mapview);
mapView.setBuiltInZoomControls(true);
mapView.setSatellite(false);
// dismiss balloon upon single tap of MapView (iOS behavior)
mapView.setOnSingleTapListener(new OnSingleTapListener() {
public boolean onSingleTap(MotionEvent e) {
itemizedOverlay.hideAllBalloons();
return true;
}
});
mapOverlays = mapView.getOverlays();
drawable = getResources().getDrawable(R.drawable.ic_launcher);
itemizedOverlay = new SimpleItemizedOverlay
(drawable, mapView);
itemizedOverlay.setShowClose(false);
itemizedOverlay.setShowDisclosure(true);
itemizedOverlay.setSnapToCenter(false);
class DownloadWebPageTask extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... urls) {
HttpClient client = new DefaultHttpClient();
// Perform a GET request for a JSON list
HttpUriRequest request = new HttpGet
("https://dl.!!!!.com/maps.json");
// Get the response that sends back
HttpResponse response = null;
try {
response = client.execute(request);
} catch (ClientProtocolException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
// Convert this response into a readable string
String jsonString = null;
try {
jsonString = StreamUtils.convertToString
(response.getEntity().getContent());
} catch (IllegalStateException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
// Create a JSON object that we can use from the String
JSONObject json = null;
try {
json = new JSONObject(jsonString);
} catch (JSONException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try{
JSONArray jsonArray = json.getJSONArray("maps");
Log.e("log_tag", "Opening JSON Array ");
for(int i=0;i < jsonArray.length();i++)
{
JSONObject jsonObject = jsonArray.getJSONObject(i);
String latitude = jsonObject.getString("latitude");
String longitude = jsonObject.getString("longitude");
String title = jsonObject.getString("title");
String country = jsonObject.getString("country");
double lat = Double.parseDouble(latitude);
double lng = Double.parseDouble(longitude);
Log.e("log_tag", "ADDING GEOPOINT"+title);
point = new GeoPoint(
(int) (lat * 1E6),
(int) (lng * 1E6));
OverlayItem overlayItem = new OverlayItem(point, title,
country);
itemizedOverlay.addOverlay(overlayItem);
}
}catch(JSONException e) {
Log.e("log_tag", "Error parsing data "+e.toString());
}
itemizedOverlay.populateNow();
mapOverlays.add(itemizedOverlay);
if (savedInstanceState == null) {
MapController controller = mapView.getController();
controller.setCenter(point);
controller.setZoom(7);
} else {
// example restoring focused state of overlays
int focused;
focused = savedInstanceState.getInt("focused_1", -1);
if (focused >= 0) {
itemizedOverlay.setFocus
(itemizedOverlay.getItem(focused));
}
}
return jsonString; }
}
}
回答1:
The exception says all: you are trying to do a network operation by loading the maps inside the UI thread. This is a bad idea, as network access is slow and will block the UI while it is running.
You should move the maps loading into a different thread e.g. by using an AsyncTask.
Basically you define a class that extends AsyncTask and then runs the download in doInBackground() and fills the result into the view within onPostExecute().
See the Android docs for more information.
In your case you need to put this code block into the doInBackground() method:
HttpClient client = new DefaultHttpClient();
// Perform a GET request for a JSON list
HttpUriRequest request = new HttpGet("https://dl.###.com/maps.json");
// Get the response that sends back
HttpResponse response = null;
try {
response = client.execute(request);
} catch (ClientProtocolException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
// Create a JSON object that we can use from the String
JSONObject json = null;
try {
json = new JSONObject(jsonString);
} catch (JSONException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
and make sure that it returns the json object for further processing (basically the lines that follow that code) within onPostExecute()
Have a look at the docs for an example. You can also look at this code for more examples.
来源：https://stackoverflow.com/questions/13083004/not-getting-json-data-into-mapview-getting-blank-map-only