如何用适配器填充ListView

我知道这是一个非常简单的问题，但是我是Android开发中的新手，因此请放轻松。
我遇到的问题是存在于我的主要活动中的一个片段（特别是AsyncTask）中。AsyncTask将数据发送到php脚本，然后根据json格式返回数据。然后将其处理并保存到jsonlist数组。直到执行后一切正常为止，可以下载，处理良好的数据。但是，当程序到达执行后，问题就会开始出现。基本上我无法列出jsonlist到listview的所有数据

    //setting up an array
    ArrayList<HashMap<String, String>> jsonlist = new ArrayList<HashMap<String, String>>();
    //creating list view variable
    ListView listview;
    //Define work in progress dialog
    private ProgressDialog mProgressDialog;  

private class ProgressTask extends AsyncTask<String, Void, Boolean> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            // Create a progressdialog
            mProgressDialog = new ProgressDialog(getActivity());

            // Set progressdialog title
            mProgressDialog.setTitle("Please wait");

            // Set progressdialog message
            mProgressDialog.setMessage("Fetching data...");
            mProgressDialog.setIndeterminate(false);

        }

        @Override
        protected Boolean doInBackground(String... params) {
            //To do in the background
            //Define variable of JSON parser type
            JSONParser jParser = new JSONParser();

            //Pass url to json parser class to fetch and save it into array variable
            JSONArray json = jParser.getJSONFromUrl(url);

            //loop from 0 to length of an array by increasing by 1
            for (int i = 0; i < json.length(); i++) {

                //Try and catch routine to prevent any crashes
                try {
                    //Get an object defined in { ... } in original json file
                    JSONObject c = json.getJSONObject(i);

                    //Separate object by obtaining values for each of the sections
                    String vtitle = c.getString(title);
                    String vcontent = c.getString(content);
                    String vuser = c.getString(user);

                    HashMap<String, String> map = new HashMap<String, String>();

                    //Fill up an array with data extracted
                    map.put(title, vtitle);
                    map.put(content, vcontent);
                    map.put(user, vuser);

                    //Add values into jsonlist
                    jsonlist.add(map);

                } catch (JSONException e)
                {
                    //In case of any error Stack trace will be returned
                    e.printStackTrace();
                }
            }
            //Once everything has been done return null value
            return null;
        }
        @Override
        protected void onPostExecute(Boolean aBoolean) {
            //Insert all data downloaded through list adapter
            ListAdapter adapter = new SimpleAdapter(getActivity(), jsonlist, R.layout.list_activity, new String[] { title, content, user }, new int[] { R.id.title, R.id.content, R.id.user });

            // Locate the listview 
            //listview = (ListView) findViewById(R.id.list);

            // Set the adapter to the ListView
            //listview.setAdapter(adapter);

            //Get rid off dialog when operation of fetching data has been done
            if (mProgressDialog.isShowing()) {
                mProgressDialog.dismiss();
            }
        }
    }

如您所见，我已经尝试了注释的代码，但是listview = (ListView) findViewById(R.id.list);返回以下错误：

无法解析方法findViewById（int）

这使我无法执行程序。这非常令人沮丧，因为我实际上将我需要的所有数据存储在一个数组中，但是只有一行代码使我无法显示它。

我也尝试过：

    ListAdapter adapter = new SimpleAdapter(context, jsonlist, R.layout.list_activity, new String[] { title, content, user }, new int[] { R.id.title, R.id.content, R.id.user });
    setListAdapter(adapter);
    lv = getListView();

但是与以前的情况一样，返回了未解决方法的错误。这是由于片段被片段扩展并向其添加任何内容而导致崩溃的事实

public class Fragment2 extends Fragment, ListActivity {...}