Android getting strings from sqlite database to autocompletetextview

I am working on a sqlite database project on android. And
it's my first sqlite project. I read lots of article and created my app but there's a
problem that I can't find a way to solve it. I hope you can show a way for me.

The problem is when I call activity by clicking a button, the device fire up
a message ("unfortunately app stopped").

I am
trying to get strings from sqlite database to autocompletetextview.

Sqlite databasehelper class's
codes

package
            com.example.matik;

import android.content.Context;
import
            android.database.sqlite.SQLiteDatabase;
import
            android.database.sqlite.SQLiteDatabase.CursorFactory;
import
            android.database.sqlite.SQLiteOpenHelper;

public class Veritabani
            extends SQLiteOpenHelper {

 private static final String
            VERITABANI="KAYISGDATA.db";

 private static final int
            SURUM=1;

 public static final String TABLE_TODO =
            "nace";
 public static final String COLUMN_ID = "_id";
 public
            static final String COLUMN_CATEGORY = "KOD";
 public static final String
            COLUMN_SUMMARY = "ACK";
 public static final String COLUMN_DESCRIPTION =
            "TEH";

 private static final String DB_DROP = "DROP TABLE IF EXISTS
            nace";
 private static final String DATABASE_CREATE = "create table "
            

 + TABLE_TODO
 + "(" 
 + COLUMN_ID + " integer
            primary key autoincrement, " 
 + COLUMN_CATEGORY + " text not null, "
            
 + COLUMN_SUMMARY + " text not null," 
 +
            COLUMN_DESCRIPTION
 + " text not null" 
 +
            ");";

 public Veritabani(Context con, String name, CursorFactory
            factory,

 int version) {
 super(con, VERITABANI, null,
            SURUM);
 // TODO Auto-generated constructor stub

            }

 @Override
 public void onCreate(SQLiteDatabase db)
            {
 // TODO Auto-generated method stub

            db.execSQL(DATABASE_CREATE);
 db.execSQL("INSERT INTO nace (KOD,ACK,TEH)
            VALUES('01.11.07','Baklagillerin yetiştirilmesi','Tehlikeli')");}


            @Override
 public void onUpgrade(SQLiteDatabase db, int oldVersion, int
            newVersion) {
 db.execSQL(DB_DROP);
 onCreate(db);

            }


}

Activity
Class's codes

package
            com.example.matik;
import java.util.ArrayList;

import
            android.app.Activity;
import android.database.Cursor;
import
            android.database.sqlite.SQLiteDatabase;
import
            android.os.Bundle;
import
            android.widget.ArrayAdapter;

import
            android.widget.AutoCompleteTextView;
import
            android.widget.EditText;

public class Matik extends Activity
            {
 AutoCompleteTextView auto;
 EditText nc;
 EditText
            th;
 Veritabani VB;
 private ArrayAdapter
            arrayAdapter;
 ArrayList Liste = new
            ArrayList();


 @Override

            protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);

            setContentView(R.layout.activity_matik);
 Liste = new
            ArrayList();
 doldur();
 nc = (EditText)
            findViewById(R.id.editText2);
 th = (EditText)
            findViewById(R.id.editText3);
 auto = (AutoCompleteTextView)
            findViewById(R.id.autoCompleteTextView1);

 arrayAdapter = new
            ArrayAdapter(this,android.R.layout.select_dialog_item, Liste);

            auto.setThreshold(1);
 auto.setAdapter(arrayAdapter);

            }

 private void doldur() {
 SQLiteDatabase Db =
            VB.getReadableDatabase();
 Cursor c = Db.rawQuery("Select ACT From nace",
            null);
 Db.isOpen();
 while(c.moveToNext()){


            Liste.add(c.getString(c.getColumnIndex("ACT")));

            };



            }

}