Java Listview未显示数据

我正在做一个项目，但它没有工作好，所以为了让我的头脑清楚，我做了另一个项目，只是简单地检查它是否工作，但我的listview没有显示数据，我从这个网站上得到的代码每件事都是完全一样的，但数据没有显示在列表中。拜托，我被困在这里了，我真的需要一些快速的帮助。等待一些积极的回应

//主代码

public class MainActivity extends Activity {
// Declare Variables
ListView listview;
List<ParseObject> ob;
ProgressDialog mProgressDialog;
ArrayAdapter<String> adapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Get the view from listview_main.xml
    setContentView(R.layout.main);
    // Execute RemoteDataTask AsyncTask
    new RemoteDataTask().execute();
}

// RemoteDataTask AsyncTask
private class RemoteDataTask extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Create a progressdialog
        mProgressDialog = new ProgressDialog(MainActivity.this);
        // Set progressdialog title
        mProgressDialog.setTitle("Parse.com Simple ListView Tutorial");
        // Set progressdialog message
        mProgressDialog.setMessage("Loading...");
        mProgressDialog.setIndeterminate(false);
        // Show progressdialog
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
        // Locate the class table named "Country" in Parse.com
        ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                "Country");
        query.orderByDescending("_created_at");
        try {
            ob = query.find();
        } catch (ParseException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // Locate the listview in listview_main.xml
        listview = (ListView) findViewById(R.id.listview);
        // Pass the results into an ArrayAdapter
        adapter = new ArrayAdapter<String>(MainActivity.this,
                R.layout.single_item);
        // Retrieve object "name" from Parse.com database
        for (ParseObject country : ob) {
            adapter.add((String) country.get("name"));
        }
        // Binds the Adapter to the ListView
        listview.setAdapter(adapter);
        // Close the progressdialog
        mProgressDialog.dismiss();
        // Capture button clicks on ListView items
        listview.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                // Send single item click data to SingleItemView Class
                Intent i = new Intent(MainActivity.this,
                        SingleItemView.class);
                // Pass data "name" followed by the position
                i.putExtra("name", ob.get(position).getString("name")
                        .toString());
                // Open SingleItemView.java Activity
                startActivity(i);
            }
        });
    }
}

}

//main的xml文件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >

<ListView
    android:id="@+id/listview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    />

</RelativeLayout>

//用于单个项目显示

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/text"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="5sp"
android:textSize="25sp" >

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虽然您从其他地方复制了代码，但仍需要提供当前代码和日志。如果您尝试调试代码，请在

适配器附近添加（（字符串）country.get（“name”）适配器何时添加数据？刚刚添加了数据，但我不明白，因为我是初学者！我调试它，但它停止！运行程序时，
logcat
中是否有任何错误？请张贴它，如果你有任何没有任何错误，它的工作正常，但没有数据显示在listview。
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/text"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="5sp"
android:textSize="25sp" >