Problems with getText() from EditText

package ur.grades;

import java.util.ArrayList;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ContextMenu.ContextMenuInfo;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Toast;

public class Start extends Activity {
    private ListView listView;
    private static int NUM_MAXIMO_CADEIRAS=100;
    private ArrayList<String> lista = new ArrayList<String>();
    private ArrayList<String> cadeiras = new ArrayList<String>();
    private ArrayList<String> notas = new ArrayList<String>();
    int array_notas[] = new int[NUM_MAXIMO_CADEIRAS];
    private ArrayAdapter<String> adapter = null;
    EditText aux;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.listagem);
         listView = (ListView)findViewById(R.id.listView1);
        listView.setTextFilterEnabled(true);
        registerForContextMenu(listView);

        listView.setOnItemClickListener(new OnItemClickListener() {

            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                adapter.notifyDataSetChanged();
            }


        });
    }

    @Override
    protected void onStart() {

        super.onStart();


        adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, lista);
        listView.setAdapter(adapter);
    }
    //Menu de contexto
    public void onCreateContextMenu(ContextMenu menu, View v,
            ContextMenuInfo menuInfo) {
            super.onCreateContextMenu(menu, v, menuInfo);

            menu.setHeaderTitle("Editar");
            MenuInflater inflater = getMenuInflater();
            inflater.inflate(R.menu.menu, menu);
            }

    //Ao criar a aplicação, cria o menu com as devidas opções.
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_principal, menu);
        return true;
        }


  // O que fazer quando se clica num botão do Menu
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.adicionar:
            //Toast.makeText(this, "This is the Toast message", Toast.LENGTH_LONG).show();
            final AlertDialog.Builder alert = new AlertDialog.Builder(this);
            final EditText input = new EditText(this);

             LayoutInflater layoutInflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
             LinearLayout dialerLayout = (LinearLayout) layoutInflater.inflate(R.layout.input, null);
             LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT, LinearLayout.LayoutParams.FILL_PARENT);
                dialerLayout.setLayoutParams(params);


            alert.setView(dialerLayout);



            alert.setPositiveButton("Adicionar", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int whichButton) {


                    aux = (EditText)findViewById(R.id.cadeira);
                    aux.setText("lol");
                    String value = aux.getText().toString();
                    //String value2="TESTE";

                lista.add(value);
                 adapter.notifyDataSetChanged();

                }

            });

            alert.setNegativeButton("Cancelar",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int whichButton) {
                            dialog.cancel();
                        }
                    });
            alert.show();



        return true;
        default: return super.onOptionsItemSelected(item);
        }
        }


}