public IReadOnlyList<DiagramTemplate> GetDiagramTemplates()

{
  // Get all the diagram templates or a template by name
  static void RetrieveDiagramTemplates(UtilityNetwork utilityNetwork)
  {
    string templateName = "ElectricNetworkTemplate";
    using DiagramManager diagramManager = utilityNetwork.GetDiagramManager();

    // Get all templates
    IReadOnlyList<DiagramTemplate> templates = diagramManager.GetDiagramTemplates();

    // Get a template by name
    DiagramTemplate template = diagramManager.GetDiagramTemplate(templateName);
  }
}

{
  // Get all the network diagrams from a template or a diagram by name
  static void GetNetworkDiagramFromDiagramTemplates(UtilityNetwork utilityNetwork)
  {
    using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
    {
      // Get the first templates
      DiagramTemplate template = diagramManager.GetDiagramTemplates().FirstOrDefault();

      // Get the network diagrams fromt he template
      IEnumerable<NetworkDiagram> diagrams = template.GetNetworkDiagrams();

      // Get a network diagram by name
      NetworkDiagram diagram = template.GetNetworkDiagram(_diagramName);
    }
  }
}