如何缓存Json数据以脱机使用？

Question

我已经在中解析了JSON数据listview，现在想使其脱机使用。有没有一种方法可以将JSON数据保存在电话上，以便在电话离线时可以查看数据？

有人知道一个例子吗？

编辑现在可以使用：

 public class MainActivity extends ListActivity {


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        new TheTask().execute();
    }

    class TheTask extends AsyncTask<Void, Void, JSONArray> {
        InputStream is = null;
        String result = "";
        JSONArray jArray = null;

        ProgressDialog pd;

        @Override
        protected void onPostExecute(JSONArray result) {
            super.onPostExecute(result);
            pd.dismiss();
            ArrayList<String> list= new ArrayList<String>();
            try {
                for(int i=0;i<result.length();i++) {

                    JSONObject jb = result.getJSONObject(i) ;
                    String name = jb.getString("name")+" "+jb.getString("Art");
                    list.add(name);
                }
            } catch(Exception e) {
                e.printStackTrace();
            }
            setListAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, list));
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pd = ProgressDialog.show(MainActivity.this, "State",
                    "Loading...", true);
        }

        @Override
        protected JSONArray doInBackground(Void... arg0) {
            ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

                try {
                    HttpClient httpclient = new DefaultHttpClient();
                    HttpPost httppost = new HttpPost("***");
                    HttpResponse response = httpclient.execute(httppost);
                    HttpEntity entity = response.getEntity();
                    is = entity.getContent();
                } catch (Exception e) {
                    Log.e("log_tag", "Error in http connection " + e.toString());
                }

                // Convert response to string
                try {
                    BufferedReader reader = new BufferedReader(new InputStreamReader(
                            is, "iso-8859-1"), 8);
                    StringBuilder sb = new StringBuilder();
                    String line = null;
                    while ((line = reader.readLine()) != null) {
                        sb.append(line + "\n");
                    }
                    is.close();
                    result = sb.toString();
                    writeToFile(result);
                } catch (Exception e) {
                    Log.e("log_tag", "Error converting result " + e.toString());
                }

                try {
                    jArray = new JSONArray(result);
                } catch (JSONException e) {
                    Log.e("log_tag", "Error parsing data " + e.toString());
                }

                try {
                    jArray = new JSONArray(readFromFile());
                } catch (JSONException e) {
                    Log.e("log_tag", "Error parsing data " + e.toString());
                }

            return jArray;
        }
    }

    private void writeToFile(String data) {
        try {
            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput("config.txt", Context.MODE_PRIVATE));
            outputStreamWriter.write(data);
            outputStreamWriter.close();
        }
        catch (IOException e) {
            Log.e("Exception", "File write failed: " + e.toString());
        }
    }

    private String readFromFile() {

        String ret = "";

        try {
            InputStream inputStream = openFileInput("config.txt");

            if ( inputStream != null ) {
                InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
                BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
                String receiveString = "";
                StringBuilder stringBuilder = new StringBuilder();

                while ( (receiveString = bufferedReader.readLine()) != null ) {
                    stringBuilder.append(receiveString);
                }

                inputStream.close();
                ret = stringBuilder.toString();
            }
        } catch (FileNotFoundException e) {
            Log.e("login activity", "File not found: " + e.toString());
        } catch (IOException e) {
            Log.e("login activity", "Can not read file: " + e.toString());
        }

        return ret;
    }
}

Answer 1

您有两种方法。您可以创建一个数据库，然后将所有数据保存在那里，并在需要时将其取回。或者，如果您拥有的数据不是很多，并且您不想处理数据库，那么您可以将json字符串写入存储卡中的文本文件，并在离线时稍后阅读。

对于第二种情况，每次您上线时，都可以从Web服务中检索相同的json并将其覆盖到旧的json中。这样，您可以确保已将最新的json保存到设备中。