Question

我正在关注this将JSON解析数据存储到SQLite数据库中，但每当我离线使用我的应用程序时，都不会将存储数据存入ListView。

我的现有代码还有什么可以实现的吗？

MainActivity.java： -

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        databaseHelper=new CategoryHelper(MainActivity.this);
        contactList = new ArrayList<HashMap<String, String>>();

        ListView lv = getListView();

        // Listview on item click listener
        lv.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {


            }
        });

        // Calling async task to get json
        new GetContacts().execute();
    }

    /**
     * Async task class to get json by making HTTP call
     * */
    private class GetContacts extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Showing progress dialog
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
            pDialog.show();

        }

        @Override
        protected Void doInBackground(Void... arg0) {
            // Creating service handler class instance
            ServiceHandler sh = new ServiceHandler();

            // Making a request to url and getting response
            String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);

            Log.d("Response: ", "> " + jsonStr);

            if (jsonStr != null) {
                try {
                    JSONObject jsonObj = new JSONObject(jsonStr);

                    // Getting JSON Array node
                    contacts = jsonObj.getJSONArray(TAG_CONTACTS);

                    // looping through All Contacts
                    for (int i = 0; i < contacts.length(); i++) {
                        JSONObject c = contacts.getJSONObject(i);

                        String id = c.getString(TAG_ID);
                        String name = c.getString(TAG_NAME);

                        databaseHelper.saveCategoryRecord(id,name);

                        // tmp hashmap for single contact
                        HashMap<String, String> contact = new HashMap<String, String>();

                        // adding each child node to HashMap key => value
                        contact.put(TAG_ID, id);
                        contact.put(TAG_NAME, name);

                        // adding contact to contact list
                        contactList.add(contact);
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            } else {
                Log.e("ServiceHandler", "Couldn't get any data from the url");
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();
            /**
             * Updating parsed JSON data into ListView
             * */
            ListAdapter adapter = new SimpleAdapter(
                    MainActivity.this, contactList,
                    R.layout.list_item, new String[] { TAG_NAME }, new int[] { R.id.name });

            setListAdapter(adapter);
        }

    }

Answer 1

我不知道ServiceHandler是什么，但我猜测当你离线时对makeServiceCall()的调用会返回null。这意味着您没有填充contactList，这意味着您在创建ListAdapter时它是空的。

我猜你想做什么，是向else添加一个if (jsonStr != null)子句，用你的数据库中的记录填充contactList。如何执行此操作取决于CategoryHelper的实现详细信息。

Answer 2

请参阅此链接，我希望这对您的要求非常有帮助。click here

Answer 3

使用共享偏好是一种更好的方法。请按照以下步骤操作：

搜索并下载GSON库。这将简化我们保存和从共享首选项中检索JSON的任务，并让您的应用使用GSON库

示例：

SharedPreferences prefs = getSharedPreferences("mySharedPreferenceKey");
Editor editor = prefs.edit();
Gson gson = new Gson();

//convert your object to string and save it to shared preference
ArrayList<Integer> myIntArrs = new ArrayList<Integer>();
editor.putString("myJSONKey", new Gson().toJson(myIntArrs)).commit();

//get your json string from shared preferences
public final Type ARRAYLIST_INTEGER = new TypeToken<ArrayList<Integer>>(){}.getType(); 
ArrayList<Integer> intArrs = gson.fromJson(prefs.getString("myJSONKey", "{}"), ARRAYLIST_INTEGER);

//do something with your intArrs

希望这有帮助！

JSON数据存储到SQLite

3 个答案: