Android-在Listview中显示来自适配器的数据

我目前有一个应用程序，可从mysql数据库中提取数据并以原始JSON格式显示。我目前正在将这些数据推送到String变量中，并将其显示在特定活动的Listview上。问题是，当尝试显示此数据时，我的Listview没有填充；我确定变量不是空的，因为if语句将捕获此变量。

这是MainActivity代码的片段：

//Methods to grab information from abhandym_DB database
public void getJSON(View view){
new BackgroundTask().execute();
}

public void parseJSON(View view){
if(JSON_String==null){
    Toast.makeText(getApplicationContext(), "First Get Json", Toast.LENGTH_LONG).show();
}else{
    Intent intent = new Intent(this,Test.class);
    intent.putExtra("JSON_Data",JSON_String);
    startActivity(intent);
}
}

class BackgroundTask extends AsyncTask<Void,Void,String>{

    String json_url;

    @Override
    protected void onPreExecute() {
        json_url = "http://abhandyman.x10host.com/json_get_data.php";
    }

    @Override
    protected String doInBackground(Void... params) {
        try {
            URL url = new URL(json_url);
            HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
            InputStream inputSteam = httpURLConnection.getInputStream();
            BufferedReader buffereredReader = new BufferedReader(new InputStreamReader(inputSteam));
            StringBuilder stringBuilder = new StringBuilder();
            while((JSON_String = buffereredReader.readLine())!=null){
            stringBuilder.append(JSON_String+"\n");
            }
            buffereredReader.close();
            inputSteam.close();
            httpURLConnection.disconnect();
            return stringBuilder.toString().trim();

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }

    @Override
    protected void onPostExecute(String result) {
        TextView textView = (TextView)findViewById(R.id.fragment1_textview_JSONAPPEAR);
        textView.setText(result);
        JSON_String = result;
    }
}

这是我的Test.java的代码

public class Test extends AppCompatActivity {
String JSON_String;
JSONObject jsonObject;
JSONArray jsonArray;
DataAdapter dataAdapter;
ListView listView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.test_layout);
    listView = (ListView)findViewById(R.id.test_listView);
    dataAdapter = new DataAdapter(this, R.layout.row_layout);
    listView.setAdapter(dataAdapter);
    JSON_String = getIntent().getExtras().getString("JSON_Data");
    try {
        jsonObject = new JSONObject(JSON_String);
        jsonArray = jsonObject.getJSONArray("server_response");
        int count = 0;
        String jobid,problem,resolution;
        while(count<jsonObject.length()){
            JSONObject JO = jsonArray.getJSONObject(count);
            jobid = JO.getString("jobid");
            problem = JO.getString("problem");
            resolution = JO.getString("resolution");
            Data data = new Data(jobid,problem,resolution);
            dataAdapter.add(data);
            count++;
        }
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

}

这是我的DataAdapter的代码：

public class DataAdapter extends ArrayAdapter{
List list = new ArrayList();
public DataAdapter(Context context, int resource) {
    super(context, resource);
}

public void add(Data object) {
    super.add(object);
    list.add(object);
}

@Override
public int getCount() {
    return list.size();
}

@Override
public Object getItem(int position) {
    return list.get(position);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View row;
    row = convertView;
    DataHolder dataHolder;
    if(row == null){
        LayoutInflater layoutInflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        row = layoutInflater.inflate(R.layout.row_layout,parent,false);
        dataHolder = new DataHolder();
        dataHolder.tx_jobid = (TextView) row.findViewById(R.id.tx_jobid);
        dataHolder.tx_problem = (TextView) row.findViewById(R.id.tx_problem);
        dataHolder.tx_resolution = (TextView) row.findViewById(R.id.tx_resolution);
        row.setTag(dataHolder);
    }else{
    dataHolder = (DataHolder)row.getTag();
    }
    Data data = (Data)this.getItem(position);
    dataHolder.tx_jobid.setText(data.getJobid());
    dataHolder.tx_problem.setText(data.getProblem());
    dataHolder.tx_resolution.setText(data.getResolution());
    return row;
}

static class DataHolder{
TextView tx_jobid,tx_problem,tx_resolution;
}

}

这是单击“解析JSON”按钮时显示的内容。

listView填充后为空

为什么不显示任何帮助或建议，将不胜感激！

提前致谢！