How to position a form on top of another form without taking the focus

My application needs to display a popup near the cursor position of any active application when certain conditions are met (known by my app).

So I would like to display the form (without stealing the focus from the active application). I tried using ShowWindow with the SW_SHOWNOACTIVATE param but, this way, the my form is displayed unde开发者_如何学运维r the currently active form.

How can I force my form to be displayed on top of any form active on the screen without stealing the input focus?

Thanks.

What you want is to use the TopMost property of the form you want to stay on top.

You need to add a bit of plumbing to the pop-up form so you can override the WM_ACTIVATE message:

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == WM_ACTIVATE)
        {
            if (((int)m.WParam & 0xFFFF) != WA_INACTIVE)
            {
                if (m.LParam != IntPtr.Zero)
                {
                    SetActiveWindow(m.LParam);
                }
                else
                {
                    // Could not find sender, just in-activate it.
                    SetActiveWindow(IntPtr.Zero);
                }
            }
        }

        base.WndProc(ref m);
    } 

Make sure you add the following to your pop-up form as well:

    [DllImport("user32.dll")]
    private extern static IntPtr SetActiveWindow(IntPtr handle);
    private const int WM_ACTIVATE = 6;
    private const int WA_INACTIVE = 0;

You can use the pop-up form as you would any other, by calling Show() on it. You can make it the top-most window through the TopMost property, as with other forms.