数据不会显示在Android的Listview中

Question

我想从google api获取谷歌地点数据并在列表视图中显示。我成功获取数据并设置为适配器，但无法在列表视图中显示。

MainActivity。 java的

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    lv=(ListView)findViewById(R.id.listView); 

    StringBuilder sbValue = new StringBuilder(sbMethod()); 
    PlacesTask placesTask = new PlacesTask(); 
    placesTask.execute(sbValue.toString()); 

    MyAdapter adapter=new MyAdapter(MainActivity.this,R.layout.my_adapter_item,arr); 
    lv.setAdapter(adapter); 
} 

public StringBuilder sbMethod() { 

    //use your current location here 
    double mLatitude =-33.8670522; 
    double mLongitude =151.1957362; 

    StringBuilder sb = new StringBuilder("https://maps.googleapis.com/maps/api/place/nearbysearch/json?"); 
    sb.append("location=" + mLatitude + "," + mLongitude); 
    sb.append("&radius=5000"); 
    sb.append("&types=" + "restaurant"); 
    sb.append("&sensor=true"); 
    sb.append("&key=AIzaSyC2SaN5I5u2eWw3zr4OZoLwD0qvCU-_uUw"); 

    Log.d("Map", "api: " + sb.toString()); 

    return sb; 
} 

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 ParserTask 
     parserTask.execute(result); 
    } 
} 

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 downloading", e.toString()); 
    } finally { 
     iStream.close(); 
     urlConnection.disconnect(); 
    } 
    return data; 
} 


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; 
     Place_JSON placeJson = new Place_JSON(); 

     try { 
      jObject = new JSONObject(jsonData[0]); 

      places = placeJson.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) { 



     for (int i = 0; i < list.size(); i++) { 
      HashMap<String, String> hmPlace = list.get(i); 
      double lat = Double.parseDouble(hmPlace.get("lat")); 
      double lng = Double.parseDouble(hmPlace.get("lng")); 

     } 
    } 
} 

public class Place_JSON { 

    /** 
    * Receives a JSONObject and returns a list 
    */ 
    public List<HashMap<String, String>> parse(JSONObject jObject) { 

     JSONArray jPlaces = null; 
     try { 
      /** Retrieves all the elements in the 'places' array */ 
      jPlaces = jObject.getJSONArray("results"); 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 
     /** Invoking getPlaces with the array of json object 
     * where each json object represent a place 
     */ 
     return getPlaces(jPlaces); 
    } 

    private List<HashMap<String, String>> getPlaces(JSONArray jPlaces) { 
     int placesCount = jPlaces.length(); 
     List<HashMap<String, String>> placesList = new ArrayList<HashMap<String, String>>(); 
     HashMap<String, String> place = null; 

     /** Taking each place, parses and adds to list object */ 
     for (int i = 0; i < placesCount; i++) { 
      try { 
       /** Call getPlace with place JSON object to parse the place */ 
       place = getPlace((JSONObject) jPlaces.get(i)); 
       placesList.add(place); 
      } catch (JSONException e) { 
       e.printStackTrace(); 
      } 
     } 
     return placesList; 
    } 

    /** 
    * Parsing the Place JSON object 
    */ 
    private HashMap<String, String> getPlace(JSONObject jPlace) { 

     HashMap<String, String> place = new HashMap<String, String>(); 
     String placeName = "-NA-"; 
     String vicinity = "-NA-"; 
     String latitude = ""; 
     String longitude = ""; 
     String reference = ""; 

     try { 
      // Extracting Place name, if available 
      if (!jPlace.isNull("name")) { 
       placeName = jPlace.getString("name"); 
      } 

      // Extracting Place Vicinity, if available 
      if (!jPlace.isNull("vicinity")) { 
       vicinity = jPlace.getString("vicinity"); 
      } 

      latitude = jPlace.getJSONObject("geometry").getJSONObject("location").getString("lat"); 
      longitude = jPlace.getJSONObject("geometry").getJSONObject("location").getString("lng"); 
      reference = jPlace.getString("reference"); 

      place.put("place_name", placeName); 
      place.put("vicinity", vicinity); 
      place.put("lat", latitude); 
      place.put("lng", longitude); 
      place.put("reference", reference); 

      map1=new HashMap<String, String>(); 
      map1.put("Name",placeName); 
      map1.put("Vicinity",vicinity); 
      arr.add(map1); 

      Log.w("MainActivity",placeName+";"+vicinity); 

     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 
     return place; 
    } 
} 

我在这里从HashMap<String, String> getPlace(JSONObject jPlace)获取数据和设置到适配器。

这个适配器我设置为在Oncreate列表视图。

适配器类

public class MyAdapter extends BaseAdapter { 
    ArrayList<HashMap<String, String>> names; 
    int data; 
    Context ctxt; 
    LayoutInflater inflater; 

    public MyAdapter (Context c, int nes, ArrayList<HashMap<String, String>> enj){ 
     this.ctxt = c; 
     this.data = nes; 
     this.names = enj; 
    } 

    @Override 
    public int getCount() { 
     // TODO Auto-generated method stub 
     return names.size(); 
    } 

    @Override 
    public Object getItem(int arg0) { 
     // TODO Auto-generated method stub 
     return names.get(arg0); 
    } 

    @Override 
    public long getItemId(int arg0) { 
     // TODO Auto-generated method stub 
     return arg0; 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup viewGroup) { 
     // TODO Create the cell (View) and populate it with an element of the array 
     ViewHolder holder = new ViewHolder(); 
     if (convertView == null) { 
      convertView = LayoutInflater.from(ctxt).inflate(data, viewGroup); 
      holder.nam = (TextView) convertView . findViewById (R.id.name); 
      holder.vic = (TextView) convertView . findViewById (R.id.vicinity); 
      convertView.setTag(holder); 
     } else { 
      holder = (ViewHolder) convertView . getTag(); 
     } 

     holder.nam.setText(names.get(position).get("Name")); 
     holder.vic.setText(names.get(position).get("Vicinity")); 
     return convertView; 
    } 
    class ViewHolder { 
     TextView nam,vic; 
    } 
} 

这里我不能够在列表视图中显示的数据。请帮助我。

Answer 1

一旦“arr”发生了变化，我们需要通知适配器该数据集已更改。在ParserTask的onPostExecute，添加以下行

adapter.notifyDataSetChanged(); 

Answer 2

尝试使用：

，而不是这个

@Override 
    public Object getItem(int arg0) { 
     // TODO Auto-generated method stub 
     return names.get(arg0); 
    } 

使用

@Override 

    public Object getItem(int arg0) { 
     // TODO Auto-generated method stub 
     return arg0; 
    }