public NetworkDiagramConsistencyState GetConsistencyState()

{
  static List<NetworkDiagram> GetInconsistentDiagrams(UtilityNetwork utilityNetwork)
  {
    // Get the DiagramManager from the utility network
    using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
    {
      List<NetworkDiagram> networkDiagrams = 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)
        {
          networkDiagrams.Add(diagram);
        }
        else
        {
          diagram.Dispose(); // If we are not returning it we need to Dispose it
        }
      }

      return networkDiagrams;
    }
  }
}

{
  // Get the NetworkDiagram from a DiagramLayer and check its ConsistencyState
  static void GetDiagram(DiagramLayer diagramLayer)
  {
    NetworkDiagram diagram = diagramLayer.GetNetworkDiagram();

    // Get the consistency state from the layer
    DiagramLayerConsistencyState diagramLayerConsistencyState = diagramLayer.ConsistencyState;

    // Or from the diagram
    NetworkDiagramConsistencyState diagramConsistencyState = diagram.GetConsistencyState();
  }
}