java - 将 JSON 存储到 SharedpReferences

Question

我正在 Android 中实现 JSON 解析。应用程序连接到 url 以检索 JSON 并返回字符串，一切正常。现在我想将 JSON 字符串存储到 ShareReferences，以便用户在没有互联网连接的情况下仍然可以看到 ListView。这是我的代码

if (isInternetPresent) { //check internet connection
                ServiceHandler sh = new ServiceHandler();
                listDataHeader = new ArrayList<String>();
                listDataChild = new HashMap<String, List<TVSchedModel>>();
                // Making a request to url and getting response
                jsonStr = sh.makeServiceCall(URL, ServiceHandler.GET); //connect to url and return a string
                Editor editor = sharedpreferences.edit();
                editor.putString("JSON", jsonStr);
                editor.commit();
            } else {
                getActivity().runOnUiThread(new Runnable() {
                    public void run() {
                        Toast.makeText(getActivity(),
                                "Cannot connect to server", Toast.LENGTH_SHORT)
                                .show();
                    }
                });
                jsonStr = sharedpreferences.getString("JSON", "");
                Log.i("JSON Shared", jsonStr);
            }
            try {
                JSONObject jsonObj = new JSONObject(jsonStr);
                // Getting JSON Array node
                JSONArray chan = jsonObj.getJSONArray(TAG_CHANNEL);
                for (int i = 0; i < chan.length(); i++) {
                    listDataHeader.add(chan.getJSONObject(i).getString(
                            "Channel"));
                    JSONArray sched = jsonObj.getJSONArray(chan
                            .getJSONObject(i).getString("Channel"));
                    List<TVSchedModel> result = new ArrayList<TVSchedModel>();
                    for (int k = 0; k < sched.length(); k++) {
                        result.add(convertSchedList(sched.getJSONObject(k)));
                    }
                    listDataChild.put(listDataHeader.get(i), result);
                }

                listAdapter.setHeaderList(listDataHeader);
                return listDataChild;
            } catch (Throwable t) {
                t.printStackTrace();
            }

如果我有互联网连接，该应用程序运行正常。然后我关闭互联网，再次运行应用程序并收到此错误，即使我收到了 Log.i(...) 中显示的字符串

04-07 23:59:30.066: W/System.err(22797): java.lang.NullPointerException
04-07 23:59:30.066: W/System.err(22797):    at com.pnminh.dfytask.TVSchedFragment$AsyncListViewLoader.doInBackground(TVSchedFragment.java:187)
04-07 23:59:30.066: W/System.err(22797):    at com.pnminh.dfytask.TVSchedFragment$AsyncListViewLoader.doInBackground(TVSchedFragment.java:1)
04-07 23:59:30.066: W/System.err(22797):    at android.os.AsyncTask$2.call(AsyncTask.java:287)
04-07 23:59:30.066: W/System.err(22797):    at java.util.concurrent.FutureTask.run(FutureTask.java:234)
04-07 23:59:30.066: W/System.err(22797):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
04-07 23:59:30.066: W/System.err(22797):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
04-07 23:59:30.066: W/System.err(22797):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
04-07 23:59:30.066: W/System.err(22797):    at java.lang.Thread.run(Thread.java:841)

我在这里做错了什么？ 谢谢

Answer 1

错误来自这一行:

listDataHeader.add(chan.getJSONObject(i).getString("Channel"));

我敢打赌，当未检测到连接时，listDataHeader 为 null，这是因为您只是在该 block 中初始化该对象:

if (isInternetPresent) {
  ...
}

只需在此 block 外部(上方)对其进行初始化，即可使其即使在没有连接时也可访问。