Hi,

It's calling IList.Item and IList.Count, this is the untyped version, so not
IList<T>.  IList and IList<T> are both implemented by Collection<T> from
which BindingList inherits.

It's not impossible to override this, but because it's an interface method
you're re-implementing and not overriding a virtual function you can't
access the base version, so if you override IList.Item you can no longer use
((IList)base).Item.

public class MyBindingList: BindingList, IList
{
    // reimplement interface
    object IList.this[int Index]
    {
          get { return ..... }
          set { ... }
    }
    .... implement all others ...
}

--- But i already told you this isn't the best way.  You better get the
items out of the BindingList and put them into a seperate List<T>. Example:

public class MyBindingList<T> : BindingList<T>
 {
   private List<T> invisableItems = new List<T>();

   public void SimpleFilter(Predicate<T> FilterPredicate)
   {
     // reset filter, add all invisble items to BindingList
     foreach (T item in invisableItems)
       base.Items.Add(item);

     invisableItems.Clear();

     // apply filter, if predicate!=null
     if (FilterPredicate != null)
     {
       // loop all items in bindingList
       for (int idx = Items.Count-1; idx >= 0; --idx)
       {
         // check if it needs to be included or not
         if (!FilterPredicate(Items[idx]))
         {
           // add to invisibleItems
           invisableItems.Add(Items[idx]);

           // remove from bindingList
           Items.RemoveAt(idx);
         }
       }
     }

     // fire reset list (for ui)
     OnListChanged(
       new ListChangedEventArgs(
       ListChangedType.Reset, -1));
   }
 }

Usage:

MyBindingList<Customer> list = new MyBindingList<Customer>();
list.Add( new Customer( ... ) );
list.Add( new Customer( ... ) );
list.Add( new Customer( ... ) );

// using anonymous methods (new in C#)
// filter so that only customers whose name start with B are visible
list.SimpleFilter( (Predicate<Customer>) delegate(Customer c)
 {
   if ( c.Name.StartWith("B") ) return true;  // include
   else return false; // exclude
 } );

// clear filter
list.SimpleFilter( null );

HTH,
Greetings