Collection property of a class

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C#

user-controls

This feels like a stupid question, but it's been driving me insane for a while now.

I have a user control with a property 'Items' that is of type List<subitem>
sub item just consists of a string and an icon image.

Whenever I customize it at design-time it's fine. But when I run the application, it resets the property back to it's default empty collection. I assume I have to set the appropriate attribute on the property to allow the compiler to serialize it or something... But so far I've had no luck. Help me pleeeeeease?!

Extract:

public class ListDisplay : UserControl
{
  private SubItemCollection mSubItems = new SubItemCollection();
  public SubItemCollection SubItems
  {
    get { return mSubItems; }
    set { mSubItems = value; }
  }
}

public class SubItemCollection : List<subitem> { ... }
public class SubItem { ... }
</subitem>