NullPointerException createViewFromResource Error

Question

How can i deal with this error need help. i have asked the question before and did all the suggested things but still getting the same error, please anyone tell me that why exactly the error is coming !

FATAL EXCEPTION: main
java.lang.NullPointerException
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)
at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
at android.widget.AbsListView.obtainView(AbsListView.java:2045)
at android.widget.ListView.makeAndAddView(ListView.java:1772)
at android.widget.ListView.fillDown(ListView.java:672)
at android.widget.ListView.fillFromTop(ListView.java:732)
at android.widget.ListView.layoutChildren(ListView.java:1625)
at android.widget.AbsListView.onLayout(AbsListView.java:1875)
at android.view.View.layout(View.java:11390)
at android.view.ViewGroup.layout(ViewGroup.java:4332)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:930)
at android.view.View.layout(View.java:11390)
at android.view.ViewGroup.layout(ViewGroup.java:4332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:444)
at android.view.View.layout(View.java:11390)
at android.view.ViewGroup.layout(ViewGroup.java:4332)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1653)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1511)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1416)
at android.view.View.layout(View.java:11390)
at android.view.ViewGroup.layout(ViewGroup.java:4332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:444)

here is the code

public class Donar_Acceptor_list 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.donar_acceptor_list);
    // 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(Donar_Acceptor_list.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 "Data" in Parse.com
        ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                "Data");
        query.orderByDescending("_created_at");
        query.whereEqualTo("DonAcc", "donar");
        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.list);
        // Pass the results into an ArrayAdapter
        //adapter = new ArrayAdapter<String>(this, 
          //      android.R.layout.activity_list_item, android.R.id.text1,username);
   // Correct one  
        adapter = new ArrayAdapter<String>(Donar_Acceptor_list.this,
                R.layout.donar_aceptor_discription);

     //  adapter= new ArrayAdapter<String>(this, R.layout.donar_aceptor_discription);
        // Retrieve object "name" from Parse.com database
        for (ParseObject names : ob) {
            adapter.add((String) names.get("username"));
        }
        // 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(Donar_Acceptor_list.this,
                        Donar_Acceptor_Discription.class);
                // Pass data "name" followed by the position
                i.putExtra("username", ob.get(position).getString("username")
                        .toString());
                // Open SingleItemView.java Activity
                startActivity(i);
            }
        }); } } }

for description

   public class Donar_Acceptor_Discription extends Activity {
   // Declare Variables
   TextView txtname;
   String username;

   @Override
   public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Get the view from singleitemview.xml
    setContentView(R.layout.single_item_view);
   // txtname=(TextView) findViewById(R.id.text);
    // Retrieve data from MainActivity on item click event
    Intent i = getIntent();
    // Get the name
    username = i.getStringExtra("username");
    // Locate the TextView in singleitemview.xml
    txtname = (TextView) findViewById(R.id.name);
    // Load the text into the TextView
    txtname.setText(username);}
   }

// layout for donar acceptor description

<?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" >

</TextView>