WinForms ComboBox SelectedIndexChanged not firing when typing few chars followed by Alt+Down

Question

In short

When I type a character in a ComboBox, press Alt+Down followed by Enter or Tab, the SelectedIndexChanged event doesn\'t fire, even though the S

Answer 1

I had the ESC problem on a DropDownList-style combobox. I slightly modified what worked for me to accommodate your needs:

public class MyComboBox : System.Windows.Forms.ComboBox
{
  private bool _sendSic;

  protected override void OnPreviewKeyDown(System.Windows.Forms.PreviewKeyDownEventArgs e)
  {
    base.OnPreviewKeyDown(e);

    if (DroppedDown)
    {
      switch(e.KeyCode)
      {
        case System.Windows.Forms.Keys.Escape:
          _sendSic = true;
          break;
        case System.Windows.Forms.Keys.Tab:
        case System.Windows.Forms.Keys.Enter:
          if(DropDownStyle == System.Windows.Forms.ComboBoxStyle.DropDown)
            _sendSic = true;
          break;
      }
    }
  }

  protected override void OnDropDownClosed(System.EventArgs e)
  {
    base.OnDropDownClosed(e);

    if(_sendSic)
    {
      _sendSic = false;
      OnSelectedIndexChanged(System.EventArgs.Empty);
    }
  }
}

What this does is listening to keystrokes that come in while the dropdown is open. If it's ESC, TAB or ENTER for a DropDown-style ComboBox or ESC for a DropDownList-style ComboBox, a SelectedIndexChanged-Event is triggered when the DropDown is closed.
I have never ever used ComboBoxStyle.Simple and don't really know how it does or should work, but since it to the best of my knowledge never displays a DropDown, this should be safe even for that style.

If you don't want to derive from ComboBox to build your own control, you can also apply similar logic to a ComboBox on a form by subscribing to it's PreviewKeyDown and DropDownClosed events.