Show control inside user control outside the boundaries of its parent

Question

I have a usercontrol that has a textbox and a listbox, and it uses them to provides autocomplete functionality to the users.

However, I want the listbox to be drawn

Answer 1

Problem is, you can't escape your container form bounds, but you can host your control somewhere else.

Here's what I got working by abusing the ToolstripDropDown class (I use it to display datepickers in a large enterprise application):

/// 

/// PopupHelper
/// 
public sealed class PopupHelper : IDisposable
{
    private readonly Control m_control;
    private readonly ToolStripDropDown m_tsdd;
    private readonly Panel m_hostPanel; // workarround - some controls don't display correctly if they are hosted directly in ToolStripControlHost

    public PopupHelper(Control pControl)
    {
        m_hostPanel = new Panel();
        m_hostPanel.Padding = Padding.Empty;
        m_hostPanel.Margin = Padding.Empty;
        m_hostPanel.TabStop = false;
        m_hostPanel.BorderStyle = BorderStyle.None;
        m_hostPanel.BackColor = Color.Transparent;

        m_tsdd = new ToolStripDropDown();
        m_tsdd.CausesValidation = false;

        m_tsdd.Padding = Padding.Empty;
        m_tsdd.Margin = Padding.Empty;
        m_tsdd.Opacity = 0.9;

        m_control = pControl;
        m_control.CausesValidation = false;
        m_control.Resize += MControlResize;

        m_hostPanel.Controls.Add(m_control);

        m_tsdd.Padding = Padding.Empty;
        m_tsdd.Margin = Padding.Empty;

        m_tsdd.MinimumSize = m_tsdd.MaximumSize = m_tsdd.Size = pControl.Size;

        m_tsdd.Items.Add(new ToolStripControlHost(m_hostPanel));
    }

    private void ResizeWindow()
    {
        m_tsdd.MinimumSize = m_tsdd.MaximumSize = m_tsdd.Size = m_control.Size;
        m_hostPanel.MinimumSize = m_hostPanel.MaximumSize = m_hostPanel.Size = m_control.Size;
    }

    private void MControlResize(object sender, EventArgs e)
    {
        ResizeWindow();
    }

    /// 

    /// Display the popup and keep the focus
    /// 
    /// 
    public void Show(Control pParentControl)
    {
        if (pParentControl == null) return;

        // position the popup window
        var loc = pParentControl.PointToScreen(new Point(0, pParentControl.Height));
        m_tsdd.Show(loc);
        m_control.Focus();
    }

    public void Close()
    {
        m_tsdd.Close();
    }

    public void Dispose()
    {
        m_control.Resize -= MControlResize;

        m_tsdd.Dispose();
        m_hostPanel.Dispose();
    }
}

Usage:

    private PopupHelper m_popup;
    private void ShowPopup()
    {
        if (m_popup == null)
            m_popup = new PopupHelper(yourListControl);

        m_popup.Show(this);
    }