I have added the following method to my listbox. It is designed to select all or none, or invert the selection only when the listbox is set for MultiSelect. All and none work just fine. Invert on the other hand does not. When I pass that parameter into the method, the method selects all.

Any thoughts?

Thanks for you help.

LPARAMETERS pcSelectionType

** parameter and property check
IF VARTYPE(pcSelectionType) # "C" OR !this.MultiSelect
    RETURN
ENDIF

LOCAL llSelectionState, lnThisItem

vNewVal = UPPER(vNewVal)
DO CASE
    CASE pcSelectionType = "ALL"
        llSelectionState = .T.
    CASE pcSelectionType = "NONE"
        llSelectionState = .F.
    CASE pcSelectionType = "INVERT"
        llSelectionState = .NULL.
    OTHERWISE
        RETURN
ENDCASE

** do this or nothing will be selected
this.SetFocus()

FOR lnThisItem = 1 TO this.ListCount
    this.Selected(lnThisItem) = IIF(ISNULL(llSelectionState), !this.Selected(lnThisItem), llSelectionState)
ENDFOR