The operating system sends the UDN_DELTAPOS notification message to the parent window of an up-down control when the position of the control is about to change. This happens when the user requests a change in the value by pressing the control's up or down arrow. The UDN_DELTAPOS message is sent before the WM_VSCROLL or WM_HSCROLL message that actually changes the control's position. This lets you examine, allow, modify, or disallow the change. The UDN_DELTAPOS message is sent in the form of a WM_NOTIFY message.
UDN_DELTAPOS
pnmud = (NM_UPDOWN FAR *) lParam
Parameters
pnmud
Pointer to an NM_UPDOWN structure that contains information about the position change.
The iPos member of this structure contains the current position of the control.
The iDelta member of the structure is a signed integer that contains the proposed change in position. If the user has clicked on the up button, this is a positive value. If the user has clicked on the down button, this is a negative value.
Return Values
Return TRUE in response to this message to prevent the change in the control's position.
Return FALSE to allow the change in the control's position.
See Also