WPF Combobox SelectedItem hell - wpf

Question

Im having a very funny issue in WPF
Im creating a Combobox through code, and adding it to a control.
When I set the Combobox.SelectedItem or Combobox.SelectedIndex or Combobox.SelectedValue I am unable to select another option from the Combox items.
ForeignKeyDisplayAttribute attribute = (ForeignKeyDisplayAttribute)this.GetAttribute(typeof(ForeignKeyDisplayAttribute), property);
if (attribute != null)
{
ForeignKeyDisplayAttribute fkd = attribute;
Type subItemType = fkd.ForeignKeyObject;
contentControl = new ComboBox();
object blankItem = System.Activator.CreateInstance(subItemType, new object[] { });
System.Reflection.MethodInfo method = subItemType.GetMethod("Load", new Type[] { typeof(int) });
object innerValue = method.Invoke(null, new object[] { value });
System.Collections.IList selectedSubItems = (System.Collections.IList)subItemType.GetMethod("Load", Type.EmptyTypes).Invoke(null, new object[] { });
selectedSubItems.Insert(0, blankItem);
((ComboBox)contentControl).SelectedValuePath = fkd.IdField;
((ComboBox)contentControl).DisplayMemberPath = fkd.DescriptionField;
((ComboBox)contentControl).ItemsSource = selectedSubItems;
((ComboBox)contentControl).InvalidateVisual();
// If I use any of the two below lines or SelectedItem then I can't change the value via the UI.
((ComboBox)contentControl).SelectedIndex = this.FindIndex(selectedSubItems, value);
((ComboBox)contentControl).SelectedValue = value;
}
Any idea's as to how I can fix this?

Answer 1

Well found the answer.
Turns out I had incorrectly coded the overridden object Equals method, and it was always returning false.
public override bool Equals(object obj)
{
if (obj is IId)
return this.Id.Equals(((IId)obj).Id);
return false;
}
should have been
public override bool Equals(object obj)
{
if (obj.GetType() == this.GetType() && obj is IId)
return this.Id.Equals(((IId)obj).Id);
return false;
}

Answer 2

Do you have Bindings on those ComboBox items in GUI? Then the simple reason is: setting a value manually in the code behind destroys the binding.
Workarround:
Before setting the value manually you can get the binding with the BindingOperations static functions.
Binding b = BindingOperations.GetBinding(yourComboBox, ComboBox.SelectedItemProperty);
// do your changes here
BindingOperations.SetBinding(yourComboBox, ComboBox.SelectedItemProperty, b);
Jan