/// <summary>
/// Shows the specified Form as a popup window, keeping the
/// Owner's title bar active and preparing to cancel the popup
/// should the user click anywhere outside the popup window.
/// <para>Typical code to use this message is as follows:</para>
/// <code>
/// frmPopup popup = new frmPopup();
/// Point location = this.PointToScreen(new Point(button1.Left, button1.Bottom));
/// popupHelper.ShowPopup(this, popup, location);
/// </code>
/// <para>Put as much initialisation code as possible
/// into the popup form's constructor, rather than the <see cref="System.Windows.Forms.Load"/>
/// event as this will improve visual appearance.</para>
/// </summary>
/// <param name="Owner">Main form which owns the popup</param>
/// <param name="Popup">Window to show as a popup</param>
/// <param name="v">Location relative to the screen to show the popup at.</param>
public void ShowDropDown(Form Owner, Form DropDown, Point Location)
{
_owner = Owner;
_dropDown = DropDown;
Application.AddMessageFilter(_filter); // Start checking for the popup being cancelled
DropDown.StartPosition = FormStartPosition.Manual; // Set the location of the popup form:
DropDown.Location = Location;
Owner.AddOwnedForm(DropDown); // Make it owned by the window that's displaying it:
DropDownClosedHandler = new EventHandler(Popup_Closed); // Respond to the Closed event in case the popup is closed by its own internal means
DropDown.Closed += DropDownClosedHandler;
_dropDownShowing = true; // Show the popup:
DropDown.Show();
DropDown.Activate();
// A little bit of fun. We've shown the popup, but because we've kept the main window's
// title bar in focus the tab sequence isn't quite right. This can be fixed by sending a tab,
// but that on its own would shift focus to the second control in the form. So send a tab,
// followed by a reverse-tab.
UIApiCalls.keybd_event((byte)Keys.Tab, 0, 0, 0);
UIApiCalls.keybd_event((byte)Keys.Tab, 0, UIApiCalls.KEYEVENTF_KEYUP, 0);
UIApiCalls.keybd_event((byte)Keys.ShiftKey, 0, 0, 0);
UIApiCalls.keybd_event((byte)Keys.Tab, 0, 0, 0);
UIApiCalls.keybd_event((byte)Keys.Tab, 0, UIApiCalls.KEYEVENTF_KEYUP, 0);
UIApiCalls.keybd_event((byte)Keys.ShiftKey, 0, UIApiCalls.KEYEVENTF_KEYUP, 0);
_filter.DropDown = DropDown; // Start filtering for mouse clicks outside the popup
}
/// <summary>
/// Subclasses the owning form's existing Window Procedure to enables the
/// title bar to remain active when a popup is show, and to detect if
/// the user clicks onto another application whilst the popup is visible.
/// </summary>
/// <param name="m">Window Procedure Message</param>
protected override void WndProc(ref Message m)
{
base.WndProc(ref m);
if (DropDownShowing)
{
if (m.Msg == UIApiCalls.WM_NCACTIVATE)
{
if (((int)m.WParam) == 0) // Check if the title bar will made inactive:
{ // Note it's no good to try and consume this message; if you try to do that you'll end up with windows
UIApiCalls.SendMessage(this.Handle, UIApiCalls.WM_NCACTIVATE, 1, IntPtr.Zero); // If so reactivate it.
}
}
else if (m.Msg == UIApiCalls.WM_ACTIVATEAPP)
{
if ((int)m.WParam == 0) // Check if the application is being deactivated.
{
CloseDropDown(); // It is so cancel the popup:
UIApiCalls.PostMessage(this.Handle, UIApiCalls.WM_NCACTIVATE, 0, IntPtr.Zero); // And put the title bar into the inactive state:
}
}
}
}