WM_NOTIFY message takes the following parameters:
wParam= identifier of the control sending the message
lParam= pointer to a
hwndFrom= handle of the control sending the message
idFrom= identifier of the control sending the message
code= notification code
- other fields depending on the notification code
Notice that the identifier of the control sending the message appears in two places, once in the
wParam and again in the
idFrom. What's the difference?
There is no difference. It's just a convenience. The same value is passed in both places, and you can check whichever one is easier for you. You might use the
wParam because it avoids having to dereference a pointer. You might use the
NMHDR because that way you have only one thing to pass to your
OnNotify helper function.
Whatever floats your boat.
Passing the same information multiple ways is hardly new. The
WM_ message also passes redundant information: The control identifier is passed in the low word of the
wParam, and you can also get it by calling
GetDlgCtrlID on the window handle passed in the