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How to put a combo box into a Popup and prevent the dropdown from closing when clicked on it?

Platform: WinForms |
Control: PopupControlContainer


Normally, when you put a combo box into a popup, the popup will be hidden when you click on the combo box drop-down. This is because the popup framework expects the windows you activate to be .NET control based, otherwise it just gives up.

To work around this problem, use a custom PopupControlContainer, as follows. Check out the inline comments.


public class CustomPopupControlContainer : PopupControlContainer


  public CustomPopupControlContainer()



  public CustomPopupControlContainer(IContainer container):this()




  public override bool IsRelatedControl ( System.Windows.Forms.Control control , System.Boolean askPopupParent )


   bool isrelated = base.IsRelatedControl(control, askPopupParent);

   // This will be the case when native windows without dotnet wrappers are encountered

   // like the combo box dropdown.

   if(control == null && !isrelated)


    // If so, then go ahead and get a dotnet parent control.

    IntPtr hwnd = GetFocus();

    // This method goes up the hierarchy looking for a dotnet parent.

    Control dotnetParent = PopupUtils.GetADotNetParentControl(hwnd);

    if(dotnetParent != null)

    // if found then check if that is a related control, instead.

    isrelated |= base.IsRelatedControl(dotnetParent, askPopupParent);


   return isrelated;


[DllImport("user32.dll", CharSet=CharSet.Auto, CallingConvention=CallingConvention.Winapi)]

public static extern IntPtr GetFocus();

[DllImport("user32.dll", CharSet=CharSet.Auto, ExactSpelling=true, CallingConvention=CallingConvention.Winapi)]

public static extern IntPtr GetParent(IntPtr hwnd);}

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