Edit string collection in VS2010 collection editor

As all my my doubts are used to vanish here... :) I have got an other question.

I have a custom control in which I have a list of strings List and I'd like the user of my control to be able to edit the list in the properties editor but I doesn't work.. I can click on the button to make the Collection editor visible but the add key is not enabled and there's a message 'Property editing is not available'.

I made a custom quick and dirty class

    public class DataUrl
{
    public string Url {get; set;}
    public DataUrl() { }
    public override string ToString()
    {
        return Url.ToString();
开发者_如何转开发    }
}

and with this it works but its... I suspect it doesn't work because string (or String) does not have a parameter-less constructor. I also tried to use the attribute

[NewItemTypesAttribute(typeof(string))]

but worthless.. Could someone help me ?

---

 public class DataUrl : Component 
 {
      private readonly List<string> _urlList = new List<string>();

      public DataUrl() : base() {}

      public DataUrl(IContainer container) : base()
      {
         container.Add(this);

         InitializeComponent();
      }

      [Editor("System.Windows.Forms.Design.StringCollectionEditor, System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", typeof(System.Drawing.Design.UITypeEditor))]
      [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]        
      public List<string> UrlList { get { return _urlList; } }          

      public override string ToString()
      {
         return Url.ToString();
      }
}