How to callback MultiObjectEntryState.OnObjectRemoved() ?

Bentley.CifNET.GeometryModel.Tool.GeometryCommand.MultiObjectEntryState used to handle object in Bentley.CifNET.Graphics.IViewport.

Whenever I click an object in the IViewport with the mouse Left button, the object is added to a "container" in the MultiObjectEntryState class some where.
and then,the protected override void OnObjectAdded(IButtonEvent buttonEvent, ObjectKey key) had been callback.

NOW,My question is:
How do I remove this object from MultiObjectEntryState's "container" ?

I knewn in MultiObjectEntryState,similar to OnObjectAdded(), there is protected override void OnObjectRemoved(IButtonEvent buttonEvent, ObjectKey key)

But I don't know how to do to callback the OnObjectRemoved.

Explain what I said about the "container", when OnAfterSelection(IObjectKeyCollection selectedKeys) was callback, selectedKeys is the "container"。