Disable/Enable Toolbar buttons.

For a Popup Menu Item { "BricscadApp.IAcadPopupMenuItem" }, there exists a way to Disable(grey out) an item by setting a bool member {" Enable { set; get; }" }.
With this member, the PopupMenuItem in PopupMenu can be enabled/disabled.
But the similar operation does not seems possible from a Toolbar item { "BricscadApp.AcadToolbarItem" }.
Is there a way to enable/disable toolbar item?