The BN_CLICKED notification message is sent when the user clicks a button. The parent window of the button receives this notification message through the WM_COMMAND message. Unlike the other button notification messages, this message is intended for applications written for any version of Windows.
BN_CLICKED idButton = (int) LOWORD(wParam); // identifier of button hwndButton = (HWND) lParam; // handle of button
A disabled button does not send a BN_CLICKED notification message to its parent window.