save isExpanded state

Hallo,

I have a listbox wich i populate with several items. I group these items by placing them in an exapnder. Problem is that when i refresh the listbox all the expanders get closed. Im trying to find a way to preserve the expanders state. Who can help.

This is what i have until now. Below is the important part: the listbox. One thing i have ben trying with: the EspandersState class. And the last: the collection of items for the listbox.

<UserControl.Resources><UserControl.Resources>
more resource here</UserControl.Resources><ListBox ItemsSource="{Binding}" ItemTemplateSelector="{StaticResource templateSelector}" 
                     Name="myListBox" 
                     HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" BorderBrush="Transparent"><ListBox.GroupStyle><GroupStyle><GroupStyle.ContainerStyle><Style TargetType="{x:Type GroupItem}"><Setter Property="Template"><Setter.Value><ControlTemplate TargetType="{x:Type GroupItem}"><Expander IsExpanded="{Binding Source={StaticResource myExpMgr}, Path=[Items[0].ObjectType]}"><Expander.Header><StackPanel Orientation="Horizontal" ><TextBlock Text="{Binding Path=Name}" /></StackPanel></Expander.Header><ItemsPresenter /></Expander></ControlTemplate></Setter.Value></Setter></Style></GroupStyle.ContainerStyle></GroupStyle></ListBox.GroupStyle></ListBox>

class ExpandersState
    {
        public Dictionary<object, bool> expandStates = new Dictionary<object, bool>();

        public bool this[object key]
        {
            get
            {
                if (!expandStates.ContainsKey(key)) return false;
                return expandStates[key];
            }
            set
            {
                if (!expandStates.ContainsKey(key)) expandStates.Add(this,value);
                expandStates[key] = value;
            }
        }
    }

 public ICollectionView GroupedProperties;
        private void setSelectedObject(object selectedDevice)
        {
            List<DependencyPropertyInfo> _listProperties = TypeHelper.GetObjectProperties(selectedDevice);

            GroupedProperties = new ListCollectionView(_listProperties);
            GroupedProperties.GroupDescriptions.Add(new PropertyGroupDescription("GroupType"));

            this.DataContext = GroupedProperties;
        }

Jc