http://help.infragistics.com/doc/WPF/2016.1/CLR4.0/?page=InfragisticsWPF4.Controls.Charts.XamDiagram.v16.1~Infragistics.Controls.Charts.XamDiagram_members.html

I have attached an example with this post can you please suggest the right event? I would like to retain TreeDiagramLayout implemented by infragistics and no custom layout is required.

Also, I would like user to be able to move diagram nodes horizontally and restrict any vertical movement in diagram.

http://ko.infragistics.com/help/wpf/xamdiagram-configuring-the-layout

Let me know if you have any questions.

Hello Abs,

The diagram layout is applied only initially to the diagram. If the items are added/removed later (eg. view model collection), the layout is not automatically applied. In order to rearrange the nodes at a later stage, call the RefreshLayout method directly on the XamDiagram.

eg.

mainWindow.Diagram.RefreshLayout();

For more details please visit:
http://ko.infragistics.com/help/wpf/xamdiagram-configuring-the-layout

If you require a custom position you can use the diagram's items collection changed event to do so:

eg.

   private void Items_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            FamilyTreeViewModel vm = this.Diagram.DataContext as FamilyTreeViewModel;

            if (e.NewStartingIndex >= vm.FamilyTree.Count)
            {
                if (e.NewItems[0] is DiagramNode)
                {

                    DiagramNode newlyAdded = e.NewItems[0] as DiagramNode;
   
                    newlyAdded.Position = new Point(50, 50);
                }
               
            }
        }

Let me know if you have any questions regarding this matter.