How do I get data from a callback into my form?

[richw42]

My program analyzes MIDI information.
I have a VB6 callback function, which the system calls when MIDI messages arrive. It works in the development environment, but when I make a .exe, it crashes when I try to modify the form. I presume this is illegal, and I somehow need to get the information from the callback function back to a form procedure. What is the best way to do this?

Details:

At form_load time, I open a MIDI input stream like this:

ret = midiInOpen(midiInHnd, midiInDev, AddressOf MidiInProc, 0, CALLBACK_FUNCTION)

MidiInProc gets called when MIDI messages arrive. When I try to do something like this:

MidiMon.lblMsgCounts(stat) = Str(MessageCounts(stat))
 

the program crashes when it is compiled to a .exe.

Unhandled exception in MidiM.exe (OLEAUT32.DLL): 0C0000005: Access Violation

So I presume that I need to push dwParam1 and dwParam2 into some kind of FIFO, and retrieve the information in a form procedure. I started looking at PostMessage and GetMessage, but I'm worried that this may be a dead end, and haven't tried it. It seems there must be a simpler method.

PostMessage(NULL, WM_USER, dwParam1, dwParam2)
GetMessage(msg, NULL, WM_USER, WM_USER)

[hazzainuk]

I think you may be right about it being a dead end. The thing that I find most interesting is that it is not crashing in your module. It is crashing in OLEAUT32.DLL under Access Violation. This probably means one of the functions you have called is attempting to read from an invalid memory address.