Question

I am writing a UserControl that will act kinda like a drop down list, basically a textbox with a listbox that pops up underneath it…

If the control is at the bottom of its parent form, I do not want the listbox to be clipped by the forms bottom, so from what I gather I cant just have this listbox as a child of the parent form.. I need to create a new borderless form containing the listbox and display this in the right position.

I can do this fine, the problem comes with sorting out the z-order of the forms. I need this new form to appear above the parent form at all times. But I dont want this window to appear above any windows that are above the parent form… which is what setting form.TopMost would give me.

Is there any other way to do this? How do ComboBoxes manage to achieve this behaviour?

Thanks

Answer 1

When you call form.Show(), pass in the user control’s owner (the current form) as the owner parameter. This code isn’t perfect, but you’ll get the idea.

class MyControl : UserControl
{
    private DropDownForm form = new DropDownForm();

    public MyControl()
    {
        form.FormClosed += dropdownform_closed;
    }

    private void MethodThatShowsDropdown()
    {
        form.AddData(GetTheData());
        form.Show(this.Owner); // Or is it "this.Parent"?  I can never remember...
    }

    private void dropdownform_closed(object sender, EventArgs e)
    {
        DoSomething(form.SelectedValue);
    }
}