CheckBox controls
The ThreeState property specifies whether or not the control can have three states. Typically, the state toggles between selected and not selected. For check boxes, if the ThreeState property has been enabled, the state of the control also toggles to a third state. A grayed-out mark is displayed for the third state.
To allow the check box to have three states:
Select the ThreeState check box on the General page of the control’s Properties view.
The ThreeState property takes a boolean value. The following lines specify that a CheckBox can have three states and that it starts out in the third state:
cbx_1.ThreeState = TRUE
cbx_1.ThirdState = TRUE
