引起的是:java.lang.nullpointerexception,不幸的是,应用程序已停止



将json数据获取到mapView中,但我仍在获得地图,但是没有地图位置,我在JSON文件中给出了映射,并且每当我运行我的应用程序时,请遵守此应用程序,请访问此应用程序,但请停止并停止应用程序。logcat说: -

 10-27 13:02:18.573: E/AndroidRuntime(719): Caused by: java.lang.NullPointerException
 10-27 13:02:18.573: E/AndroidRuntime(719):     at com.erachnida.restaurant.versionoct.MapView.onCreate(MapView.java:52)

请参阅以下代码: -

public class MapView extends MapActivity {
public GeoPoint point;
TapControlledMapView mapView; // use the custom TapControlledMapView
List<Overlay> mapOverlays;
Drawable drawable;
SimpleItemizedOverlay itemizedOverlay;
JSONObject json = null;
@Override
protected void onCreate(final Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    mapOverlays = mapView.getOverlays();
    drawable = getResources().getDrawable(R.drawable.ic_launcher);
    itemizedOverlay = new SimpleItemizedOverlay(drawable, mapView);
    itemizedOverlay.setShowClose(false);
    itemizedOverlay.setShowDisclosure(true);
    itemizedOverlay.setSnapToCenter(false);
    new AsyncTask<Void, Void, Void>() {

        @Override
        protected Void doInBackground(Void... params) {
            // TODO Auto-generated method stub
            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();
            }
            return null;
        }
        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);

            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));
                }
            }
        }
    }.execute();
}

AsyncTask在另一个线程内执行doInBackground()中的所有内容,该线程无法访问您的视图的GUI。

preExecute()postExecute()在此新线程中发生繁重之前和之后,您可以访问GUI,您甚至可以将长操作的结果传递给postExecute(),然后显示处理的任何结果。

在这里查看我的答案。

尝试遵循它的完美,但要给你想法。

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    mapOverlays = mapView.getOverlays();
    drawable = getResources().getDrawable(R.drawable.ic_launcher);
    itemizedOverlay = new SimpleItemizedOverlay(drawable, mapView);
    itemizedOverlay.setShowClose(false);
    itemizedOverlay.setShowDisclosure(true);
    itemizedOverlay.setSnapToCenter(false);
    new AsyncTask<Void, Void, Void>() {

        @Override
        protected Void doInBackground(Void... params) {
            // TODO Auto-generated method stub
            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();
            }
            return null;
        }
        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);

            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));
                }
            }
        }
    }.execute();
}

您阅读了此吗?

Asynctask中,doinBackground()方法在由Asynctask创建的单独线程中执行,这实际上是使任务async减少UIThread

上的负载的目的

执行doInBanckground()

后,onPostExecute()方法确实在UIThread中执行

doInBackground中执行某些任务后,您需要看到的更改必须在onPostExecute中写入,例如,如果您在doInBackground中执行某些WebService操作,则可以使用ProgressDialog解散它是在onPostExecute中编写的。p>或者在您的情况下,您的json数组分配数组值必须在onPostExecute中写入。

编辑尝试此代码,因为我不确定mapview刚刚尝试过。

    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());
           } 

           return jsonString;
       }
           @Override
        protected void onPostExecute(String result) {
 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));
               }
           }
              }
    }

您没有初始化TapControlledMapView对象。初始化并尝试。

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