ArcGIS Pro 2.6 API Reference Guide
CustomItemBase Class
Members 

ArcGIS.Desktop.Core Namespace : CustomItemBase Class
Base class for deriving custom items. Custom items are shown in the Catalog View and Pane
Object Model
CustomItemBase ClassItem ClassTimeInstant Class
Syntax
public abstract class CustomItemBase : Item, IMetadata, System.ComponentModel.INotifyPropertyChanged  
Public MustInherit Class CustomItemBase 
   Inherits Item
   Implements IMetadata, System.ComponentModel.INotifyPropertyChanged 
Remarks
Custom items that have a physical file representation on disk should registered their file extension within the Config.daml so that they can be browsed within Folder collection in Catalog. Registration is within the esri_customItems category and should include the fileExtension of your custom item and keywords that can be used in the Catalog search. Note: The Pro SDK template for custom items will automatically generate a set of Config.daml entries for you.
Custom items that can contain child items should set IsContainer=true. The custom item Fetch method is called when the item is first expanded in the Catalog to allow custom items to retrieve their child items
Inheritance Hierarchy

System.Object
   ArcGIS.Desktop.Framework.Contracts.PropertyChangedBase
      ArcGIS.Desktop.Core.Item
         ArcGIS.Desktop.Core.CustomItemBase
            ArcGIS.Desktop.Core.CustomProjectItemBase

Requirements

Target Platforms: Windows 10, Windows 8.1, Windows 7

See Also

Reference

CustomItemBase Members
ArcGIS.Desktop.Core Namespace