C#

using System;<br />
using System.Windows.Forms;<br />
using System.ComponentModel;<br />
<br />
class Supplier {<br />
  public string Id { get; set; }<br />
}<br />
<br />
class Form1 : Form {<br />
  [STAThread]<br />
  static void Main() {<br />
    Application.Run(new Form1());<br />
  }<br />
<br />
  public Form1() {<br />
    DataGridView grid = new DataGridView();<br />
    // if this line is commented out, all is OK:<br />
    grid.EditMode = DataGridViewEditMode.EditOnEnter;<br />
    ComboBoxColumn comboBoxColumn = new ComboBoxColumn();<br />
    ComboBoxCell ComboBoxCell = new ComboBoxCell();<br />
    comboBoxColumn.CellTemplate = ComboBoxCell;<br />
    grid.Columns.Add(comboBoxColumn);<br />
    BindingList<Supplier> l = new BindingList<Supplier>();<br />
    l.Add(new Supplier());<br />
    grid.DataSource = l;<br />
    Controls.Add(grid);<br />
  }<br />
<br />
  class ComboBoxColumn : DataGridViewComboBoxColumn { }<br />
<br />
  class ComboBoxCell : DataGridViewComboBoxCell {<br />
    public override Type EditType {<br />
      get {<br />
        return typeof(ComboBoxEditingControl);<br />
      }<br />
    }<br />
<br />
  }<br />
<br />
  class ComboBoxEditingControl : ComboBox, IDataGridViewEditingControl {<br />
    protected int rowIndex;<br />
    protected DataGridView dataGridView;<br />
    protected bool valueChanged = false;<br />
<br />
    protected override void OnTextChanged(EventArgs e) {<br />
      base.OnTextChanged(e);<br />
      NotifyDataGridViewOfValueChange();<br />
    }<br />
<br />
    protected virtual void NotifyDataGridViewOfValueChange() {<br />
      valueChanged = true;<br />
      if (dataGridView != null) {<br />
        dataGridView.NotifyCurrentCellDirty(true);<br />
      }<br />
    }<br />
<br />
    public Cursor EditingPanelCursor {<br />
      get {<br />
        return Cursors.IBeam;<br />
      }<br />
    }<br />
<br />
    public DataGridView EditingControlDataGridView {<br />
      get {<br />
        return dataGridView;<br />
      }<br />
      set {<br />
        dataGridView = value;<br />
      }<br />
    }<br />
<br />
    public object EditingControlFormattedValue {<br />
      set {<br />
        if (value.ToString() != Text) {<br />
          Text = value.ToString();<br />
          NotifyDataGridViewOfValueChange();<br />
        }<br />
      }<br />
<br />
      get {<br />
        return Text;<br />
      }<br />
    }<br />
<br />
    public object GetEditingControlFormattedValue(DataGridViewDataErrorContexts<br />
    context) {<br />
      return Text;<br />
    }<br />
<br />
<br />
<br />
    public void PrepareEditingControlForEdit(bool selectAll) { }<br />
<br />
    public bool RepositionEditingControlOnValueChange {<br />
      get {<br />
        return false;<br />
      }<br />
    }<br />
<br />
    public int EditingControlRowIndex {<br />
      get {<br />
        return rowIndex;<br />
      }<br />
<br />
      set {<br />
        rowIndex = value;<br />
      }<br />
    }<br />
<br />
    public void ApplyCellStyleToEditingControl(DataGridViewCellStyle<br />
    dataGridViewCellStyle) {<br />
      DropDownStyle = ComboBoxStyle.DropDown;<br />
    }<br />
<br />
    public bool EditingControlWantsInputKey(Keys keyData, bool<br />
    dataGridViewWantsInputKey) {<br />
      return !dataGridViewWantsInputKey;<br />
    }<br />
<br />
    public bool EditingControlValueChanged {<br />
<br />
      get {<br />
        return valueChanged;<br />
      }<br />
      set {<br />
        valueChanged = value;<br />
      }<br />
    }<br />
  }<br />
}

class Customer<br />
    {<br />
        private string customerID;<br />
        private string companyName;<br />
<br />
        public string CustomerID<br />
        {<br />
            get { return customerID; }<br />
            set { customerID = value; }<br />
        }        <br />
<br />
        public string CompanyName<br />
        {<br />
            get { return companyName; }<br />
            set { companyName = value; }<br />
        }<br />
<br />
        public Customer() { }<br />
<br />
        public Customer(string custID, string company)<br />
        {<br />
            this.CustomerID = custID;<br />
            this.CompanyName = company;<br />
        }<br />
<br />
        public DataTable GetCustomers()<br />
        {<br />
            DataAccess da = new DataAccess("Data Source=.;Initial Catalog=Northwind;Persist Security Info=True;User ID=sa;Password=1");<br />
            DataTable dt = new DataTable();<br />
            da.ExecuteCommand(new SqlCommand("SELECT CustomerID,CompanyName FROM CUSTOMERS"),out dt);            <br />
            return dt;<br />
        }        <br />
    }

class CustomerCollection : System.Collections.CollectionBase<br />
    {<br />
        public CustomerCollection()<br />
        {<br />
<br />
        }<br />
<br />
        public void Add(Customer customer)<br />
        {<br />
            List.Add(customer);<br />
        }<br />
<br />
        public void Remove(Customer customer)<br />
        {<br />
            List.Remove(customer);<br />
        }<br />
<br />
        public Customer this[int index]<br />
        {<br />
            get<br />
            {<br />
                return (Customer)List[index];<br />
            }<br />
<br />
            set<br />
            {<br />
                base.List[index] = value;<br />
            }<br />
        }<br />
    }

Customer c = new Customer();<br />
this.dataGridView1.DataSource = c.GetCustomers();