private void cboCountry_Validating(object sender, CancelEventArgs e)
{
	if(((ComboBox)sender).Text.Length > 0)
	{
		string text = ((ComboBox)sender).Text.ToUpper();	
		bool valueFound = false;
		for(int i = 0; i < ((ComboBox)sender).Items.Count; i++)
		{
		  	if(((ComboBox)sender).Items[i].ToString().CompareTo(text) == 0)
			{
				valueFound = true;
				break;
			}
		}
		if(!valueFound)
		{
			e.Cancel = true;
		}
	}
}

private void dbReadCountries()
{
    try
    {
        this.countryArrayList.Clear();
		
		IDbCommand oraCmd = OracleDBManager.Instance.CreateDbCommand();
        oraCmd.CommandText = "SELECT * FROM COUNTRIES ORDER BY COUNTRY";
		using (IDataReader or = OracleDBManager.Instance.ExecuteReader(null, oraCmd))
		{
			while (or.Read())
			{
				this.countryArrayList.Add(new CountryItem(or["COUNTRY"].ToString(), or["	code"].ToString()));
			}
		}
        // binding DataSource to Combobox 
		
        this.cboCountry.DataSource = null;
        this.cboCountry.DisplayMember = "Text";
        this.cboCountry.ValueMember = "Name";
        this.cboCountry.DataSource = countryArrayList;
		string[] autoCompletion = new string[countryArrayList.Count];
		for(int i = 0; i < countryArrayList.Count; i++)
		{
			autoCompletion[i] = this.cboCountry.Items[i].ToString();
		}

		this.cboCountry.AutoCompleteCustomSource = new AutoCompleteStringCollection();
		this.cboCountry.AutoCompleteCustomSource.AddRange(autoCompletion);	
    }
    catch (System.Exception ex)
    {
        
    }
}