Hello, Stoyo!
I need to do the following. I need show the tooltip when mouse is over the diagram link. To do this I plan to inherit the class from DiagramLink and add 2 properties: Desription and HyperLink on the image which will shown when tooltip opens. So I create the class:

    public class TPDEDiagramLink: DiagramLink
    {
        #region Properties
        /// <summary>
        /// Gets or sets the description.
        /// </summary>
        /// <value>The description.</value>
        public String Description
        {
            get { return m_sDescription; }
            set { m_sDescription = value; }
        }
        /// <summary>
        /// Gets or sets the image hyperlink.
        /// </summary>
        /// <value>The image hyperlink.</value>
        public String ImageHLink
        {
            get { return m_sImgHLink; }
            set { m_sImgHLink = value; }
        }
        /// <summary>
        /// Gets or sets the index of the image.
        /// </summary>
        /// <value>The index of the image.</value>
        public int ImageIndex
        {
            get { return m_nImgIdxInDb; }
            set { m_nImgIdxInDb = value; }
        }
        #endregion //Properties
     }
 

And I need to serialize this properties and save them into database. I need to override functions SaveToXml(), LoadFromXml() and Clone() for make possible to copy this objects and paste them into the diagram. And the question is following: what type of DiagramLink constructor I need use in the Clone() method?
Thanks.

I set in the constructor of my user control the following:

void InitLinks()
	  {
		m_Diagram.LinkCascadeOrientation = MindFusion.Diagramming.Wpf.Orientation.Auto;
		m_Diagram.LinkSegments = 15;
		m_Diagram.Behavior = Behavior.Custom;
		m_Diagram.CustomLinkType = typeof(TPDEDiagramLink);
		m_Diagram.CustomBehavior = new LinkBehavior(m_Diagram);
		m_Diagram.LinkHeadShape = ArrowHeads.Triangle;
		m_Diagram.LinkHeadShapeSize = 10;
		m_Diagram.LinkBrush = Brushes.Black;
		m_Diagram.LinkShape = LinkShape.Cascading;
		m_Diagram.LinksSnapToBorders = false;
		m_Diagram.SnapToAnchor = SnapToAnchor.OnCreateOrModify;
	  }
 

But when I draw link in is created as DiagramLink but not as TPDEDiagramLink. What's wrong?

Yes, it helps. Thanks.