[C++/CLI] Show a child form only one instance using event

Replying an answer, I've found interesting question.
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=2906249&SiteID=1
There will be many ways to do that.

First, find window caption name or class name using FindWindow(...) native API.
But it's require an InteropServices.

Second, Do not show a new form duing a child form alive.
When a child form closed, fire an event.

I've implemented sample codes.
Here is sample codes on MSDN Forums
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=2906249&SiteID=1