Question

我正在尝试将ArrayList<ItemDTO> data传递给onPostExecute方法，但始终将null传递给onPostExecute()方法。我已经调试了它，你可以在下面的屏幕截图中看到doInBackground返回带有long, lat, route, direction值的2个元素的arrayList。我该如何解决？

enter image description here

GetLLRD课程：

public class GetLLRD {
    Context mContext;
    String json;

    public void post_selected(String json, Context context) {
        this.json = json;
        new MyAsyncTask().execute(json);
        context = this.mContext;
    }

    class MyAsyncTask extends AsyncTask<String, Integer, ArrayList<ItemDTO>> {
        ArrayList<ItemDTO> data;


        @Override
        protected ArrayList<ItemDTO> doInBackground(String... params) {

          .
          .
          .
          .

                                try {
                    Gson gson = new Gson();
                    Type listType = new TypeToken<List<ItemDTO>>() {
                    }.getType();
                    data = gson.fromJson(sb.toString(), listType);
                } catch (JsonSyntaxException e) {
                    e.printStackTrace();
                }

                for (ItemDTO itemDTO : data) {
                    double latitude = itemDTO.getLatitude();
                    double longitude = itemDTO.getLongitude();
                    int route = itemDTO.getRoute();
                    String direction = itemDTO.getDirection();
                    System.out.println(latitude + ", " + longitude + ", "
                            + ", " + route + ", " + direction);

                }
          .
          .
          .
          .     


            return data;

        }

        protected void onPostExecute(ArrayList<ItemDTO> result) {

            new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {
                    new MyAsyncTask().execute(json);
                    System.out.println("The method onPostExcute() in GETLLRD class was invoked  again");
                }
            }, 1*30 * 1000);

            if (result != null) {
                Intent intent = new Intent(mContext, Map.class);
                intent.putExtra("list",result);
                mContext.startActivity(intent); 

            }else{
                Log.e("123", "Avoiding null pointer, the dat is null in the GETLLRD class!!!");
            }

        }

    }
}

MapDataJSON：

public class MapDataJSON {
    ArrayList<ItemDTO> items;

    public MapDataJSON(ArrayList<ItemDTO> items) {
        super();
        this.items = items;
    }

    public ArrayList<ItemDTO> getItems() {
        return items;
    }

    public void setItems(ArrayList<ItemDTO> items) {
        this.items = items;
    }

    public static class ItemDTO  implements Serializable  {
        private static final long serialVersionUID = 1L; 
        double latitude;
        double longitude;
        int route;
        String direction;

        public ItemDTO(double latitude, double longitude, int route,
                String direction) {
            super();
            this.latitude = latitude;
            this.longitude = longitude;
            this.route = route;
            this.direction = direction;
        }

        public double getLatitude() {
            return latitude;
        }

        public double getLongitude() {
            return longitude;
        }

        public int getRoute() {
            return route;
        }

        public String getDirection() {
            return direction;
        }

        public void setLatitude(double latitude) {
            this.latitude = latitude;
        }

        public void setLongitude(double longitude) {
            this.longitude = longitude;
        }

        public void setRoute(int route) {
            this.route = route;
        }

        public void setDirection(String direction) {
            this.direction = direction;
        }
    }

}

JSON简单：

[
  {
    "latitude": 20.123456,
    "longitude": 70.123456,
    "route": 4,
    "direction": "ABC"
   },

   {
    "latitude": 30.123456,
    "longitude": 80.123456,
    "route": 9,
    "direction": "DEF"
   },
     {
    "latitude": 10.123456,
    "longitude": 90.123456,
    "route": 3,
    "direction": "GHI"
   }

]

Answer 1

我还没有测试过，但您可以尝试将参数设置为onPostExecute() 到

protected void onPostExecute(List<ItemDTO> result)

而不是

protected void onPostExecute(ArrayList<ItemDTO> result)

Answer 2

请在dobackground方法中尝试以下给定代码。

            Gson gson = new Gson();
            List<ResponseDetail> countriesResponseList = new ArrayList<ResponseDetail>();
            Type collectionType = new TypeToken<List<ResponseDetail>>(){}.getType();
            try {
                countriesResponseList = gson.fromJson(sb.toString(), collectionType);
            } catch (JsonSyntaxException e) {e.printStackTrace();} catch (JSONException e) {e.printStackTrace();}

Answer 3

我在下面的代码中所做的是将整个Json响应作为String返回，然后将其转换为JsonArray并循环它并提取每个对象并添加它是ArrayList。

同样客观的不同方法。

<强>代码：

 class MyAsyncTask extends AsyncTask<String, String, String> {
        ArrayList<ItemDTO> data;


        @Override
        protected String doInBackground(String... params) {

          List<NameValuePair> params = new ArrayList<NameValuePair>();

                              try {
        // Set up HTTP post

        // HttpClient is more then less deprecated. Need to change to
        // URLConnection
        HttpClient httpClient = new DefaultHttpClient();

        HttpPost httpPost = new HttpPost(YourURL);

        httpPost.setEntity(new UrlEncodedFormEntity(params));
        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();

        // Read content & Log
        inputStream = httpEntity.getContent();
    } catch (UnsupportedEncodingException e1) {
        Log.e("UnsupportedEncoding", e1.toString());
        e1.printStackTrace();
    } catch (ClientProtocolException e2) {
        Log.e("ClientProtocolException", e2.toString());
        e2.printStackTrace();
    } catch (IllegalStateException e3) {
        Log.e("IllegalStateException", e3.toString());
        e3.printStackTrace();
    } catch (IOException e4) {
        Log.e("IOException", e4.toString());
        e4.printStackTrace();
    }
    // Convert response to string using String Builder
    try {
        BufferedReader bReader = new BufferedReader(
                new InputStreamReader(inputStream, "utf-8"), 8);
        StringBuilder sBuilder = new StringBuilder();

        String line = null;
        while ((line = bReader.readLine()) != null) {
            sBuilder.append(line + "\n");
        }

        inputStream.close();
        result = sBuilder.toString();

    } catch (Exception e) {
        Log.e("StringBuildingReader",
                "Error convertingt " + e.toString());
    }
    return result;

        }

        protected void onPostExecute(String result) {
            JSONArray att = new JSONArray(result);
                    for (int i = 0; i < att.length(); i++) {
                        JSONObject jObject = att.getJSONObject(i);
                        double latitude = jObject.getDouble("latitude");
                        double longitude = jObject.getDouble("longitude");

                        int route = jObject.getInt("route");
                        String direction = jObject.getString("direction");

                         ItemDTO itme = new  ItemDTO(latitude,longitude,route,direction);
                        YourArrayList.add(item);

                    }
            //do what ever you need to do with your ArrayList here

            new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {
                    new MyAsyncTask().execute(json);
                    System.out.println("The method onPostExcute() in GETLLRD class was invoked  again");
                }
            }, 1*30 * 1000);

            if (result != null) {
                Intent intent = new Intent(mContext, Map.class);
                intent.putExtra("list",result);
                mContext.startActivity(intent); 

            }else{
                Log.e("123", "Avoiding null pointer, the dat is null in the GETLLRD class!!!");
            }

        }

    }

希望这对你有用。

onPostExecute方法收到null

3 个答案: