怎样知道ListView1被 选中

说的是ListBox吗？

List1.ListIndex 返回当前被选择项。
另外在Click和KeyDown之类的事件中加入监视代码就行

Function SelectItem(ByRef objLv As ListView, ByVal X As Single, Y As Single) As Boolean
On Error GoTo aErr
Dim objItem As ListItem
Set objItem = objLv.HitTest(X, Y)
objLv.ListItems(objItem.Index).Selected = True
SelectItem = True
Exit Function
aErr:
SelectItem = False
End Function