DN_BTNCLICK

Dialog item ID.

State of the item after the keystroke:
DI_BUTTON = 0
DI_CHECKBOX =0 (unchecked), 1 (checked) and 2 (undefined, if the DIF_3STATE flag is set)
DI_RADIOBUTTON = 0 - for the previous element in the group, 1 - for the active element in the group.

For DI_BUTTON: TRUE - if the message has been handled and it should not be processed by the kernel.
FALSE - continue processing the message by the kernel.

For other elements: TRUE - to apply the changes and redraw the control.
FALSE - to discard changes.

Control	Description
DI_BUTTON	Push Button.
DI_CHECKBOX	Check Box.
DI_RADIOBUTTON	Radio Button.