Question

我正在尝试实施一个谷歌地图应用程序，将谷歌标记存储在云数据库上。但我有一个问题是要回到云上标记的坐标。

如何将AsyncTask中生成的List返回给自定义java类？我现在遇到的问题是当我在不同的类中初始化Alistener类时，例如，在B类中：

AListener a = new Alistener( ..., ... );
  ...
  a.getMarkerData();
  List<Pair> myList = a.getList();

myList只是null，我认为因为a.getList()已经在onPostExecute()中从该云数据库中提取数据之前执行了。任何见解都会有很大帮助。

这是我的java类：

public class AListener {
protected static final String TAG = null;
double lat, lon;
List<Pair> myList = new ArrayList<Pair>();
CustomMarkerListener( double lat, double lon ) {
    this.lat = lat;
    this.lon = lon;
}

public void getMarkerData() {
    MarkerDataInfo ms = new MarkerDataInfo();
    ms.execute( UserLogin.ITEM_URI );
}
public void setList(List<Pair> myList ) {
    this.myList = myList;
}

public List<Pair> getList() {
    return this.myList;
}
}

这是我的AsyncTask AListener的内部类：

private class MarkerDataInfo extends AsyncTask<String, Void, List<Pair>> {

     List<Pair> list;
     private CustomMarkerListener mLis;
     public MarkerDataInfo() {}
     public MarkerDataInfo( CustomMarkerListener mLis ) {
         this.mLis = mLis;
     }
     @Override
     protected List<Pair> doInBackground(String... url) {
            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet( UserLogin.ITEM_URI);
            list = new ArrayList<Pair>();
            try {
                HttpResponse response = client.execute(request);
                HttpEntity entity = response.getEntity();
                String data = EntityUtils.toString(entity);
                Log.d(TAG, data);
                JSONObject myjson;
                try {
                    myjson = new JSONObject(data);
                    JSONArray array = myjson.getJSONArray("data");
                    for (int i = 0; i < array.length(); i++) {
                        JSONObject obj = array.getJSONObject(i);
                        String markerOfUser = obj.get("marker").toString();
                        if( markerOfUser.equals( UserLogin.accountName )) {
                            String latname = obj.get("lat").toString();
                            String lonname = obj.get("lon").toString();
                            double latData = Double.parseDouble(latname);
                            double lonData =  Double.parseDouble(lonname);
                            list.add( new Pair( latData, lonData ));
                        }
                    }
                } catch (JSONException e) {
                    Log.d(TAG, "Error in parsing JSON");
                }
            } catch (ClientProtocolException e) {
                Log.d(TAG, "ClientProtocolException while trying to connect to GAE");
            } catch (IOException e) {
                Log.d(TAG, "IOException while trying to connect to GAE");
            }
        return list;
    }
    protected void onPostExecute(List<Pair> list) {
        super.onPostExecute(list);
        mLis.setList( list );
        Log.d("CUstome", "" + list.size());
    }

 }

Answer 1

如果任何时候只有一个请求处于有效状态，您可以将singleton pattern用于您的课程。

如何返回AsyncTask中生成的arraylist / list

1 个答案: