Remove duplicates from listbox/combobox in WPF

Question

I've seen answers mentioning something compact like this:here

List<T> withDupes = LoadSomeData();
List<T> noDupes = withDupes.Distinct().ToList();

So I tried the following (syntax)

List<InfoControl> withDupes = (List<InfoControl>)listBox1.ItemsSource;
listBox1.ItemsSource = withDupes.Distinct().ToList();

but withDupes is null ? Perhaps I am retrieving the wrong data list. I added InfoControls one at a time.

Is there something else I should be implementing in InfoControl class? (Equal,hashCode)?

Thanks Addendum 1: [ignore I should not be translating from Java :) ] Also have (translated from a Java example, not sure it's 100% correct) declared in the InfoControl class..

public Boolean Equals(Object obj) 
{ if (obj == this) { return true; } 
if (!(obj is InfoControl)) { return false; } 

InfoControl other = (InfoControl)obj; 
return this.URL.Equals(other.URL); } 

public int hashCode() 
{ return this.URLFld.Content.GetHashCode(); } 

Addendum 2: When I try to use override based on the msdn link custom type example it says it is sealed :) It does not seem distinct is stepping thru GetHashCode() and I am still getting the same listbox.items.count after distinct.

bool IEquatable<InfoControl>.Equals(InfoControl other)
{
if (Object.ReferenceEquals(other, null)) return false;
if (Object.ReferenceEquals(this, other)) return true;
return URL.Equals(other.URL);
}

public int GetHashCode(InfoControl obj)
{
     return obj.URL.GetHashCode();
}

Addendum 3: When I try override VS2010 says it is sealed? "cannot override inherited member 'System.Windows.DependencyObject.GetHashCode()' because it is sealed" what am I doing wrong?

  public override int GetHashCode()
    {
        return URL.GetHashCode();
    }

   public string URL
    {
        get { return this.URLFld.Content.ToString() ; }
        set
        {
            this.URLFld.Content = value;
        }
    }

. Addendum 4:

   public partial class InfoControl : UserControl
         , IEquatable<YouTubeInfoControl>

    {

        private string URL_;
        public string URL
        {
            get { return URL_; }
            set
            {
                URL_ = value;
            }
        }

        bool IEquatable<YouTubeInfoControl>.Equals(YouTubeInfoControl other)
        {

            if (Object.ReferenceEquals(other, null)) return false;


            if (Object.ReferenceEquals(this, other)) return true;

            return URL == other.URL;
        }

        public override int GetHashCode()
        {
            return URL.GetHashCode();
        }

    }

Answer 1

A ListBox's items can either be set via ListBox.Items or ListBox.ItemsSource, if you add items using listBox1.Items.Add this does not affect the ItemsSource which will stay null. In this case you should get your initial list from listBox1.Items.

Answer 2

If you're adding the InfoControl objects one at a time, the ItemSource of the listBox will remain set to NULL. You're better off binding a List to the listbox which will allow you to get the data back off of the ItemSource property later