java - 从其他类调用 AsyncTack 并返回 null Android Studio

Question

我试图通过 ParseQuerys 类中的方法调用 AsyncTask，以在我的 Fragment lvRestaurantFrag 的 ListView 中使用该信息。问题是该方法返回 null，因为 AsyncTask 未到达 onPostExecute。我不知道如何解决它。

在这里我留下我的代码:

JSON

API Link

[  
   {  
      "idBranchRestaurant":1,
      "idRestaurant":1,
      "restaurant":{  
         "idRestaurant":1,
         "name":"Don Julio",
         "description":"La mejor parrilla para cualquier turista",
         "socialNetwork":[  
            {  
               "idSocialNetworkRestaurant":1,
               "idRestaurant":1,
               "idTypeSocialNetwork":1,
               "value":"www.donjulio.com.ar",
               "type":{  
                  "idTypeSocialNetwork":1,
                  "name":"Website",
                  "icon":"website_ic.jpg"
               }
            }
         ]
      },
      "idRangePriceBranch":1,
      "RangePrice":{  
         "idRangePriceBranch":1,
         "idBranchRestaurant":1,
         "minimum":300,
         "maximum":600
      },
      "name":"Paraguay",
      "photo":[  
         {  
            "idBranchPhoto":4,
            "idBranchRestaurant":1,
            "branch":null,
            "idUser":0,
            "user":null,
            "photo":"entradaDonJulio.jpg"
         }
      ],
      "cuisine":[  
         {  
            "idCousine":1,
            "name":"Parrilla"
         }
      ],
      "menu":[  
         {  
            "idTypeMenu":1,
            "name":"Mediodia",
            "idBranchRestaurant":1,
            "plates":null
         },
         {  
            "idTypeMenu":2,
            "name":"Noche",
            "idBranchRestaurant":1,
            "plates":null
         }
      ],
      "filter":[  
         {  
            "idTypeFilter":2,
            "name":"Family",
            "icon":"family_ic.jpg"
         }
      ],
      "service":[  
         {  
            "idService":2,
            "name":"Comida para celiacos"
         },
         {  
            "idService":1,
            "name":"Wifi"
         }
      ],
      "timetable":[  
         {  
            "idTimetableBranch":11,
            "idBranchRestaurant":1,
            "idDay":2,
            "openingHour":"19 hs",
            "closingHour":"24 hs",
            "day":{  
               "idDay":2,
               "name":"Tuesday"
            }
         },
         {  
            "idTimetableBranch":10,
            "idBranchRestaurant":1,
            "idDay":2,
            "openingHour":"12 hs",
            "closingHour":"16 hs",
            "day":{  
               "idDay":2,
               "name":"Tuesday"
            }
         },
         {  
            "idTimetableBranch":9,
            "idBranchRestaurant":1,
            "idDay":1,
            "openingHour":"19 hs",
            "closingHour":"24 hs",
            "day":{  
               "idDay":1,
               "name":"Monday"
            }
         },
         {  
            "idTimetableBranch":8,
            "idBranchRestaurant":1,
            "idDay":1,
            "openingHour":"12 hs ",
            "closingHour":"16 hs",
            "day":{  
               "idDay":1,
               "name":"Monday"
            }
         },
         {  
            "idTimetableBranch":12,
            "idBranchRestaurant":1,
            "idDay":3,
            "openingHour":"12 hs",
            "closingHour":"16 hs",
            "day":{  
               "idDay":3,
               "name":"Wednesday"
            }
         },
         {  
            "idTimetableBranch":13,
            "idBranchRestaurant":1,
            "idDay":3,
            "openingHour":"19 hs ",
            "closingHour":"24 hs",
            "day":{  
               "idDay":3,
               "name":"Wednesday"
            }
         },
         {  
            "idTimetableBranch":14,
            "idBranchRestaurant":1,
            "idDay":4,
            "openingHour":"12 hs",
            "closingHour":"16 hs",
            "day":{  
               "idDay":4,
               "name":"Thursday"
            }
         },
         {  
            "idTimetableBranch":15,
            "idBranchRestaurant":1,
            "idDay":4,
            "openingHour":"19 hs",
            "closingHour":"24 hs",
            "day":{  
               "idDay":4,
               "name":"Thursday"
            }
         },
         {  
            "idTimetableBranch":16,
            "idBranchRestaurant":1,
            "idDay":5,
            "openingHour":"12 hs",
            "closingHour":"16 hs ",
            "day":{  
               "idDay":5,
               "name":"Friday"
            }
         },
         {  
            "idTimetableBranch":17,
            "idBranchRestaurant":1,
            "idDay":5,
            "openingHour":"19 hs ",
            "closingHour":"2 hs",
            "day":{  
               "idDay":5,
               "name":"Friday"
            }
         }
      ],
      "latitude":"87654322",
      "longitude":"23456789",
      "calification":null,
      "averageFood":4.0,
      "averageService":4.0,
      "averageAmbience":4.0,
      "averageCalification":4.0,
      "promotion":[  
         {  
            "idPromotion":3,
            "idTypePromotion":2,
            "code":"DIADELPADRE",
            "name":"Dia Del Padre Regalo",
            "startDate":"2017-06-26T00:00:00",
            "expireDate":"2017-06-18T00:00:00",
            "description":"postre de regalo",
            "value":100,
            "type":{  
               "idTypePromotion":2,
               "name":"Gift"
            }
         }
      ]
   },
   {  
      "idBranchRestaurant":2,
      "idRestaurant":2,
      "restaurant":{  
         "idRestaurant":2,
         "name":"La Hormiga",
         "description":"el lugar explota de gente y en especial de gente de ort",
         "socialNetwork":[  
            {  
               "idSocialNetworkRestaurant":2,
               "idRestaurant":2,
               "idTypeSocialNetwork":2,
               "value":"www.facebook.com/LaHormiga",
               "type":{  
                  "idTypeSocialNetwork":2,
                  "name":"Facebook",
                  "icon":"fb_ic.jpg"
               }
            }
         ]
      },
      "idRangePriceBranch":1,
      "RangePrice":{  
         "idRangePriceBranch":1,
         "idBranchRestaurant":1,
         "minimum":300,
         "maximum":600
      },
      "name":"Ort",
      "photo":[  
         {  
            "idBranchPhoto":5,
            "idBranchRestaurant":2,
            "branch":null,
            "idUser":0,
            "user":null,
            "photo":"entradaLaHormiga.jpg"
         }
      ],
      "cuisine":[  
         {  
            "idCousine":2,
            "name":"Pizza"
         }
      ],
      "menu":[  
         {  
            "idTypeMenu":3,
            "name":"Mediodia",
            "idBranchRestaurant":2,
            "plates":null
         }
      ],
      "filter":[  
         {  
            "idTypeFilter":1,
            "name":"With Discount",
            "icon":"discount_ic.jpg"
         }
      ],
      "service":[  
         {  
            "idService":3,
            "name":"Aire acondicionado"
         },
         {  
            "idService":1,
            "name":"Wifi"
         }
      ],
      "timetable":[  
         {  
            "idTimetableBranch":18,
            "idBranchRestaurant":2,
            "idDay":6,
            "openingHour":"11 hs",
            "closingHour":"15 hs",
            "day":{  
               "idDay":6,
               "name":"Saturday"
            }
         },
         {  
            "idTimetableBranch":19,
            "idBranchRestaurant":2,
            "idDay":7,
            "openingHour":"11 hs",
            "closingHour":"15 hs",
            "day":{  
               "idDay":7,
               "name":"Sunday"
            }
         }
      ],
      "latitude":"234567897",
      "longitude":"123456789",
      "calification":null,
      "averageFood":5.0,
      "averageService":5.0,
      "averageAmbience":5.0,
      "averageCalification":5.0,
      "promotion":[  

      ]
   },
   {  
      "idBranchRestaurant":3,
      "idRestaurant":3,
      "restaurant":{  
         "idRestaurant":3,
         "name":"paja rota",
         "description":"La mejor parrilla de ramos mejia",
         "socialNetwork":[  
            {  
               "idSocialNetworkRestaurant":3,
               "idRestaurant":3,
               "idTypeSocialNetwork":3,
               "value":"twitter.com/Pajarota",
               "type":{  
                  "idTypeSocialNetwork":3,
                  "name":"Twitter",
                  "icon":"ic_twitter.png"
               }
            }
         ]
      },
      "idRangePriceBranch":3,
      "RangePrice":{  
         "idRangePriceBranch":3,
         "idBranchRestaurant":3,
         "minimum":50,
         "maximum":250
      },
      "name":"Ramos MEjia",
      "photo":[  
         {  
            "idBranchPhoto":6,
            "idBranchRestaurant":3,
            "branch":null,
            "idUser":0,
            "user":null,
            "photo":"EntradaPajaRota.jpg"
         }
      ],
      "cuisine":[  
         {  
            "idCousine":1,
            "name":"Parrilla"
         }
      ],
      "menu":[  
         {  
            "idTypeMenu":4,
            "name":"Mediodia",
            "idBranchRestaurant":3,
            "plates":null
         },
         {  
            "idTypeMenu":5,
            "name":"Noche",
            "idBranchRestaurant":3,
            "plates":null
         }
      ],
      "filter":[  
         {  
            "idTypeFilter":2,
            "name":"Family",
            "icon":"family_ic.jpg"
         }
      ],
      "service":[  
         {  
            "idService":1,
            "name":"Wifi"
         },
         {  
            "idService":4,
            "name":"Carta de braille"
         }
      ],
      "timetable":[  
         {  
            "idTimetableBranch":20,
            "idBranchRestaurant":3,
            "idDay":5,
            "openingHour":"12 hs",
            "closingHour":"16 hs",
            "day":{  
               "idDay":5,
               "name":"Friday"
            }
         },
         {  
            "idTimetableBranch":21,
            "idBranchRestaurant":3,
            "idDay":5,
            "openingHour":"19 hs",
            "closingHour":"2 hs",
            "day":{  
               "idDay":5,
               "name":"Friday"
            }
         },
         {  
            "idTimetableBranch":22,
            "idBranchRestaurant":3,
            "idDay":6,
            "openingHour":"12 hs",
            "closingHour":"16 hs",
            "day":{  
               "idDay":6,
               "name":"Saturday"
            }
         },
         {  
            "idTimetableBranch":23,
            "idBranchRestaurant":3,
            "idDay":6,
            "openingHour":"19 hs",
            "closingHour":"2 hs",
            "day":{  
               "idDay":6,
               "name":"Saturday"
            }
         },
         {  
            "idTimetableBranch":24,
            "idBranchRestaurant":3,
            "idDay":7,
            "openingHour":"12 hs",
            "closingHour":"16 hs",
            "day":{  
               "idDay":7,
               "name":"Sunday"
            }
         }
      ],
      "latitude":"12345678",
      "longitude":"87654321",
      "calification":null,
      "averageFood":5.0,
      "averageService":5.0,
      "averageAmbience":5.0,
      "averageCalification":5.0,
      "promotion":[  

      ]
   },
   {  
      "idBranchRestaurant":4,
      "idRestaurant":4,
      "restaurant":{  
         "idRestaurant":4,
         "name":"la espiga",
         "description":"el mejor lugar para comer pastas",
         "socialNetwork":[  
            {  
               "idSocialNetworkRestaurant":4,
               "idRestaurant":4,
               "idTypeSocialNetwork":4,
               "value":"instagram.com/laespiga",
               "type":{  
                  "idTypeSocialNetwork":4,
                  "name":"Instagram",
                  "icon":"ic_Instagram.png"
               }
            }
         ]
      },
      "idRangePriceBranch":4,
      "RangePrice":{  
         "idRangePriceBranch":4,
         "idBranchRestaurant":4,
         "minimum":80,
         "maximum":150
      },
      "name":"Almagro",
      "photo":[  
         {  
            "idBranchPhoto":7,
            "idBranchRestaurant":4,
            "branch":null,
            "idUser":0,
            "user":null,
            "photo":"EntradaLaEspiga.jpg"
         }
      ],
      "cuisine":[  
         {  
            "idCousine":4,
            "name":"Pasta"
         }
      ],
      "menu":[  
         {  
            "idTypeMenu":6,
            "name":"Tarde",
            "idBranchRestaurant":4,
            "plates":null
         }
      ],
      "filter":[  
         {  
            "idTypeFilter":1,
            "name":"With Discount",
            "icon":"discount_ic.jpg"
         }
      ],
      "service":[  
         {  
            "idService":1,
            "name":"Wifi"
         },
         {  
            "idService":3,
            "name":"Aire acondicionado"
         }
      ],
      "timetable":[  
         {  
            "idTimetableBranch":26,
            "idBranchRestaurant":4,
            "idDay":1,
            "openingHour":"16 hs",
            "closingHour":"19 hs",
            "day":{  
               "idDay":1,
               "name":"Monday"
            }
         },
         {  
            "idTimetableBranch":27,
            "idBranchRestaurant":4,
            "idDay":2,
            "openingHour":"16 hs",
            "closingHour":"19 hs",
            "day":{  
               "idDay":2,
               "name":"Tuesday"
            }
         },
         {  
            "idTimetableBranch":28,
            "idBranchRestaurant":4,
            "idDay":3,
            "openingHour":"16 hs",
            "closingHour":"19 hs",
            "day":{  
               "idDay":3,
               "name":"Wednesday"
            }
         },
         {  
            "idTimetableBranch":29,
            "idBranchRestaurant":4,
            "idDay":4,
            "openingHour":"16 hs",
            "closingHour":"19 hs",
            "day":{  
               "idDay":4,
               "name":"Thursday"
            }
         },
         {  
            "idTimetableBranch":30,
            "idBranchRestaurant":4,
            "idDay":5,
            "openingHour":"16 hs",
            "closingHour":"19 hs",
            "day":{  
               "idDay":5,
               "name":"Friday"
            }
         }
      ],
      "latitude":"87657467",
      "longitude":"45254567",
      "calification":null,
      "averageFood":5.0,
      "averageService":5.0,
      "averageAmbience":5.0,
      "averageCalification":5.0,
      "promotion":[  

      ]
   }
]

ParseQuery 类

private String server = "http://appmorfando.azurewebsites.net/api/";
ParsingObjects parse = new ParsingObjects();

// Query for List Branches

    private ArrayList<Branch> branches = new ArrayList<Branch>();

    public ArrayList<Branch> getAllBranch(int limit, int offset){
        new BranchGetAll().execute("branch/", limit + "", offset + "");
        return branches;
    }

    private class BranchGetAll extends AsyncTask<String, Void, ArrayList<Branch>> {

        protected void onPostExecute(ArrayList<Branch> datos) {
            super.onPostExecute(datos);
            branches = datos;
        }

        @Override
        protected ArrayList<Branch> doInBackground(String... parametros) {
            String url = parametros[0] + parametros[1] + "/" + parametros[2];

            ArrayList<Branch> branchList = new ArrayList<Branch>();

            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .url(server + url)
                    .build();
            String resultado;
            try {
                Response response = client.newCall(request).execute();  // Llamo al API Rest servicio1 en ejemplo.com
                resultado = response.body().string();
            } catch (IOException e) {
                Log.d("Error",e.getMessage());             // Error de Network
                return null;
            }

            try{
                JSONArray jsonBranch = new JSONArray(resultado);



                for (int i = 0; i < jsonBranch.length(); i++){
                    Branch b = new Branch();
                    JSONObject obj = jsonBranch.getJSONObject(i);

                    b = parse.branch(obj);
                    //Restaurant
                    JSONObject restoObj = obj.getJSONObject("restaurant");
                    b.restaurant = parse.restaurant(restoObj);

                    //Social Network
                    JSONArray socialNetwork = restoObj.getJSONArray("socialNetwork");
                    b.restaurant.social = parse.socialNetwork(socialNetwork);

                    // Range Price
                    JSONObject rangeObj = obj.getJSONObject("RangePrice");
                    b.range = parse.rangePrice(rangeObj);

                    //Photos
                    JSONArray photo = obj.getJSONArray("photo");
                    b.photo = parse.photoBranch(photo);

                    // Cuisine
                    JSONArray cuisine = obj.getJSONArray("cuisine");
                    b.cuisine = parse.cuisine(cuisine);

                    //Menu
                    JSONArray menu = obj.getJSONArray("menu");
                    b.menu = parse.menu(menu);

                    //Filter
                    JSONArray filter = obj.getJSONArray("filter");
                    b.filter = parse.filter(filter);

                    //Service
                    JSONArray service = obj.getJSONArray("service");

                    b.service = parse.service(service);

                    //Timetable
                    JSONArray timetable = obj.getJSONArray("timetable");
                    b.timetable = parse.timetable(timetable);

                    //Promotion
                    JSONArray promotion = obj.getJSONArray("promotion");
                    b.promotion = parse.promotion(promotion);

                    branchList.add(b);
                }
                return branchList;
            }
            catch (JSONException e) {
                Log.d("error", e.getMessage());
                return null;
            }
        }

    }

lvRestaurant fragment

 public class lvRestaurantFrag extends Fragment  implements AdapterView.OnItemClickListener{

    MainActivity main;
    ListView restaurantItems;
    lvRestaurantAdapter adapter;
    ParseQuery pq;

    ArrayList<Branch> listBranches;

    public View onCreateView(LayoutInflater inflater, ViewGroup group, Bundle data) {
        View toReturn;
        toReturn = inflater.inflate(R.layout.frag_restaurant_lv, group, false);
        main = (MainActivity)getActivity();
        pq = new ParseQuery();

        restaurantItems = (ListView) toReturn.findViewById(R.id.lvRestaurantItems);
        // Here gets null so the adapter size is 0
        listBranches = pq.getAllBranch(10,0);
        adapter = new lvRestaurantAdapter(listBranches, main);

        restaurantItems.setAdapter(adapter);
        restaurantItems.setOnItemClickListener(this);
        return toReturn;
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        int idBranch = adapter.getId(position);
        main.BranchSelected(idBranch);
    }
}

Answer 1

这里有两件事:

1. 你怎么知道你的异步任务没有到达onpostexecute？您附加的代码不会覆盖 onpostexecute。让我们尝试实现该方法并执行一个简单的 logcat 或 system.out 来确认。

2. 您的异步任务正在从服务器获取 Json 对象并将它们打包到要返回的列表中。有很多方法会导致此失败，例如服务器连接错误或 json 解析不正确。我会仔细测试您的连接和数据结构，以确保 null 是 asynctask 导致的。

最简单的测试方法之一是注释掉所有连接和 json 相关代码，然后返回一个您知道有效的手动填充列表。这将有助于隔离出现故障的区域。