LazControls

LazControls is a set of controls that are often used in Lazarus.

TListFilterEdit

This is a control that can easily filter a ListBox.

Once property TListFilterEdit.FilteredListBox is assigned then TListFilterEdit makes copy of ListBox.Items and works with it. If you add ListBox.Items.Add later, then these data does not appear in TListFilterEdit.

You should do always:

TListFilterEdit.FilteredListBox:=nil; //Add data to ListBox TListFilterEdit.FilteredListBox:=ListBox;