Winforms bind SelectedItems in listbox - winforms

Question

Using the standard listbox I would like to bind it to a set of objects and update a bound items collection to include those selected.
So I have something like:
_pContext = new BindingSource();
_pContext.DataSource = _gpContext;
_pContext.DataMember = "ParentEntities";
_AllChildrenListBox.DataSource = _container.ChildEntities;
_AllChildrenListBox.DataBindings.Add("MySelectedItems", _pContext, "ChildEntities", false);
_allChildrenListBox is the listbox. I created a new listbox type inheriting from ListBox so I could create an alternative SelectedItems property which would then encapsulate the logic to set/unset the items.
So the question in a nutshell is: In the above, ChildEntities is a collection of "ChildEntity" objects. My list box contains all possible ChildEntity objects and I want the elements in ChildEntities to be selected, and updated when selection changed.

Answer 1

I have found a way around this. It's a little ugly at the moment, but works. I can refine it later.
So first bit was the binding itself.
_AllChildrenListBox.DataBindings.Add("SelectedItems2", _pContext, "ChildEntities2", true);
The key here seemed to be setting the formatting parameter to true.
Next I needed something in SelectedItems2 that would do my dirty work. This is a mess, but works. Here's the full class:
public class MyListBox : ListBox
{
private IEnumerable<object> _original;
public IEnumerable<object> SelectedItems2
{
get
{
return UpdateSet();
}
set
{
SelectItems(value);
}
}
private IEnumerable<object> UpdateSet()
{
var listSource = _original as IListSource;
IList list = null;
if (listSource != null)
{
list = listSource.GetList();
}
var iList = _original as IList;
if (list == null && iList != null)
{
list = iList;
}
if (list == null)
{
return _original;
}
foreach (var item in SelectedItems)
{
if (!list.Contains(item))
{
list.Add(item);
}
}
foreach (var item in _original.ToList())
{
if (!SelectedItems.Contains(item))
{
list.Remove(item);
}
}
return _original;
}
private void SelectItems(IEnumerable<object> items)
{
_original = items;
var hashset = new HashSet<object>();
foreach (var item in items)
{
hashset.Add(item);
}
for(var i=0;i<Items.Count;i++)
{
SetSelected(i, hashset.Contains(Items[i]));
}
}
}
Essentially I'm breaking all the rules and assuming IEnumerable hides a more tasty list based interface, if it does it uses that to changes the underlying set.
Finally, I'm using EF (Entity Framework) and you can't call the setter of a collection property, so my entity currently looks like this: Notice how I'm duplicating all the list change operations which is totally unnecessary, but I did say this was just the first working go.
public partial class ParentEntity
{
public IEnumerable<object> ChildEntities2
{
get
{
return new List<object>(ChildEntities);
}
set
{
if (value == null)
{
return;
}
foreach (var item in ChildEntities.ToList().Where(item => !value.Contains(item)))
{
ChildEntities.Remove(item);
}
foreach (var item in value)
{
var cItem = item as ChildEntity;
if (cItem != null)
{
if (!ChildEntities.Contains(item as ChildEntity))
{
ChildEntities.Add(item as ChildEntity);
}
}
}
}
}
}