title: in C#, How to post a user message to an Windows and process it?
body: <p>In C++ on Windows, we use user defined message to in form UI to update data thru PostMessage API. We can use PostMessage in C# but do not know how to process user defined message in Forms!
  Some ones will tell me to use delegated and invoke but we have problems when forms closed or not already created when threads call delegated. We still prefer PostMessage to inform UI to update data.
  Please Help.</p>