How can I detect changes to GraphView, Nodes and Edges?

You've probably figured this out already, but for the sake of other people searching for answers on this forum: The key to all this is the GraphView.graphViewChanged callback. You want to do something like:

     MyGraphView() {
         graphViewChanged = OnGraphChange;
     }
 
     private GraphViewChange OnGraphChange(GraphViewChange change)
     {
         if (change.edgesToCreate != null) {
             foreach (Edge edge in change.edgesToCreate)
             {
                 ...
             }
         }
 
         if (change.elementsToRemove != null)
         {
             foreach (GraphElement e in change.elementsToRemove)
             {
                 if (e.GetType() == typeof(Edge) {
                     ...
                 }
             }
         }
 
         if (change.movedElements != null)
         {
             foreach (GraphElement e in change.movedElements)
             {
                 if (e.GetType() == typeof(Node))
                 {
                     ...
                 }
             }
         }
 
         return change;
     }