The IMN_CHANGECANDIDATE message is sent to the application when an IME is about to change the content of the candidate window. An application should process this notification message if it displays candidates itself. The application receives this notification message through the WM_IME_NOTIFY message.
fCandidates = (DWORD) lParam;
No return value.
The IME window changes the appearance of the candidate window when it processes this message. An application can get information about the system window with the ImmGetCandidateListCount and ImmGetCandidateList functions.
ImmGetCandidateList, ImmGetCandidateListCount, WM_IME_NOTIFY