NM_GETCUSTOMSPLITRECT notification code
Sent by a button control to its parent to get measurements for the two rectangles of the split button. This notification code is sent in the form of a WM_NOTIFY message.
A pointer to an NMCUSTOMSPLITRECTINFO to receive bounding rectangles information. The NMCUSTOMSPLITRECTINFO structure is sent with the notification code as a request for the parent to provide measurements for the rectangles of the split button.
This notification code is sent by a button control before it is drawn. The button must be of style BS_SPLITBUTTON or BS_DEFSPLITBUTTON. If the rectangles returned to the control in lParam are not valid, they are ignored.
Minimum supported client
|Windows Vista [desktop apps only]|
Minimum supported server
|Windows Server 2008 [desktop apps only]|
Build date: 11/16/2013