Derive a class of Diagram and outweighs the methods
override void OnSerializeTag
and
protected override void OnDeserializeTag

Calling SaveToString after LoadFromString then SaveToString, beast last call and subsequent calls are not the methods OnSerializeTag and OnDeserializeTag

EX:

In the method test (), the 2nd called SaveToString, the methods OnSerializeTag and OnDeserializeTag will not be called.



class MyDiagram : Diagram

string diagramId = "Test";

protected override void OnSerializeTag(SerializeTagEventArgs e)
{
base.OnSerializeTag(e);
XElement el;
var els = e.Context.XDocument.Root.Descendants("MyData").ToList();
if (els.Count > 0)
el = els[0];
else
{
el = new XElement("MyData");
e.Context.XDocument.Root.Add(el);
}
e.Context.WriteString(diagramId, "DiagramId", el);
}
ª
protected override void OnDeserializeTag(SerializeTagEventArgs e)
{
base.OnDeserializeTag(e);
var els = e.Context.XDocument.Root.Descendants("MyData").ToList();
if (els.Count > 0)
{
var el = els[0];
diagramId = e.Context.ReadString("DiagramId", el, Guid.NewGuid().ToString());
}
}

public void TEST()
{
           string save = this.SaveToString(SaveToStringFormat.Xml);
           this.LoadFromString(save);
           save = this.SaveToString(SaveToStringFormat.Xml);

           this.LoadFromString(save);
           save = this.SaveToString(SaveToStringFormat.Xml);
           this.LoadFromString(save);
}

}