First, thanks to all, who answered.
And, slowly the smoke is clearing. But nevertheless, the whole topic seems to be very smoky.
For clarity: I need a messaging method within one application only, one thread, not interapplication communication. Sounds very simple. One Window contains some settings, one or more other windows, which might be open at the same time, will display discrete contents depending on the settings of the settings window.
@PascalDragon: I found this document this morning too; especially the section about Dispatch is not clear.
Until now, my sight is as follows:
1. Each form, which should react to the Messages sent, has to define a message handler like this:
procedure TForm1.MyHandler(Var Msg); message <msg_ID>;
2. Invoking this handler may happen in two ways:
2.1 Defining a message record for each different message globally and passing this record to the dispatch method of
those Forms, which should react to this message. This means, that one has to address each form in the applications
code separately.
2.2 Use of Postmessage (...) or SendMessage(...) methods. I believe, that those methods address ALL of my application
objects/classes automatically; only those will react, which have an appropriate message handler definition
in their class definition (s.a.).
I will try both ways and post the corresponding projects into this thread.