At least up until Windows XP, this does not match my experience. The Win32 windows callback gets called for every message sent to it, whether the window is in the foreground or not. Especially, there are messages that get sent to set the focus to the window.

If all else fails, the controlling/sending program can force the other window into the foreground and then send the messages.

In reply to Re^2: Sending a message to Win32 Dialog in background. by Corion
in thread Sending a message to Win32 Dialog in background. by balajinagaraju

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