public sealed class NetworkDiagram : ArcGIS.Core.CoreObjectsBase, System.IDisposable  

using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
{
  // get all the diagrams
  IReadOnlyList<NetworkDiagram> diagrams = diagramManager.GetNetworkDiagrams();

  // get a diagram by name
  NetworkDiagram diagram = diagramManager.GetNetworkDiagram(diagrameName);

  // get diagrams by extent
  diagrams = diagramManager.GetNetworkDiagrams(extentOfInterest);

  // get diagrams from a set of utility network feature GlobalIDs
  diagrams = diagramManager.GetNetworkDiagrams(globalIDs);

  // get diagrams from a set of utility network feature GlobalIDs within an extent
  diagrams = diagramManager.GetNetworkDiagrams(extentOfInterest, globalIDs);
}

public List<NetworkDiagram> GetInconsistentDiagrams(UtilityNetwork utilityNetwork)
{
  // Get the DiagramManager from the utility network

  using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
  {
    List<NetworkDiagram> myList = new List<NetworkDiagram>();

    // Loop through the network diagrams in the diagram manager

    foreach (NetworkDiagram diagram in diagramManager.GetNetworkDiagrams())
    {
      NetworkDiagramInfo diagramInfo = diagram.GetDiagramInfo();

      // If the diagram is not a system diagram and is in an inconsistent state, add it to our list

      if (!diagramInfo.IsSystem && diagram.GetConsistencyState() != NetworkDiagramConsistencyState.DiagramIsConsistent)
      {
        myList.Add(diagram);
      }
      else
      {
        diagram.Dispose(); // If we are not returning it we need to Dispose it
      }
    }

    return myList;
  }
}

// Create a diagram layer from a NetworkDiagram (myDiagram)
DiagramLayer diagramLayer = await QueuedTask.Run<DiagramLayer>(() =>
{
  // Create the diagram map
  var newMap = MapFactory.Instance.CreateMap(myDiagram.Name, ArcGIS.Core.CIM.MapType.NetworkDiagram, MapViewingMode.Map);
  if (newMap == null)
    return null;

  // Open the diagram map
  var mapPane = ArcGIS.Desktop.Core.ProApp.Panes.CreateMapPaneAsync(newMap, MapViewingMode.Map);
  if (mapPane == null)
    return null;

  //Add the diagram to the map
  return newMap.AddDiagramLayer(myDiagram);
});

public void GetDiagram(DiagramLayer diagramLayer)
{
  // note - methods need to run on MCT

  NetworkDiagram diagram = diagramLayer.GetNetworkDiagram();

  // get the consistency state from the layer
  DiagramLayerConsistencyState dlState = diagramLayer.ConsistencyState;

  // or from the diagram
  NetworkDiagramConsistencyState ndState = diagram.GetConsistencyState();
}

public void CreateNetworkDiagram(UtilityNetwork utilityNetwork, IEnumerable<Guid> globalIDs)
{
  using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
  {
    // get the template
    DiagramTemplate template = diagramManager.GetDiagramTemplate(templateName);

    // create the diagram
    NetworkDiagram diagram = diagramManager.CreateNetworkDiagram(template, globalIDs);
  }
}

public void GetDiagramContent(UtilityNetwork utilityNetwork)
{
  using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
  {
    // get a diagram by name
    NetworkDiagram diagram = diagramManager.GetNetworkDiagram(templateName);

    string json_content = diagram.GetContent(true, true, true, true);
  }
}

public void DiagramElementQueryResultAndNetworkDiagramSubsetClasses(Geodatabase geodatabase, DiagramManager diagramManager, string diagramName)
{
  // Retrieve a diagram
  using (NetworkDiagram diagramTest = diagramManager.GetNetworkDiagram(diagramName))
  {
    // Create a DiagramElementQueryByElementTypes query object to get the diagram elements we want to work with
    DiagramElementQueryByElementTypes query = new DiagramElementQueryByElementTypes();
    query.QueryDiagramJunctionElement = true;
    query.QueryDiagramEdgeElement = true;
    query.QueryDiagramContainerElement = true;

    // Retrieve those diagram elements
    DiagramElementQueryResult elements = diagramTest.QueryDiagramElements(query);

    // Create a NetworkDiagramSubset object to edit this set of diagram elements
    NetworkDiagramSubset subset = new NetworkDiagramSubset();
    subset.DiagramJunctionElements = elements.DiagramJunctionElements;
    subset.DiagramEdgeElements = elements.DiagramEdgeElements;
    subset.DiagramContainerElements = elements.DiagramContainerElements;

    // Edit the shapes of the diagram elements - left as an exercise for the student
    TranslateDiagramElements(subset);

    // Save the new layout of the diagram elements
    diagramTest.SaveLayout(subset, true);
  }
}