Send/Recieve windows message between app and installer?

I have an installer that needs to communicate to the application that called it. Is there a way to send a windows message to my application and/or recieve a windows message from the calling application?

This looks too complex for NSIS script, but you can write a plug-in with additional window procedure for installer' window, NSISdl plug-in code may be a good start point for this (SetWindowLong(GWL_WNDPROC)).

Or you can add a hook ( SetWindowsHookEx(WH_MSGFILTER) ) for all parent window thread messages. MSDN also describes some other good ways for interprocess communication (like named pipes) 😉