ArcGIS Pro 2.8 API Reference Guide
CustomProjectItemContainer<T> Class
Members  Example 

ArcGIS.Desktop.Core Namespace : CustomProjectItemContainer<T> Class
The type of custom project item the container will contain
A custom project item container contains custom project items of a specific type that have been added to a project.
Syntax
Type Parameters
T
The type of custom project item the container will contain
Remarks
By default, empty project item containers are not visible in the Catalog pane or view. They only become visible once they contain at least one (custom) project item. Custom project item containers are registered in the Config.daml within the esri_core_projectContainers category. Custom project item containers have an associated "container type" which is an arbitrary unique string used to identify your container within the project container collection.
Custom project items must know their corresponding custom project item container container type.
Example
//Add an item to the project...
//This will automatically show the item's container if it is not already visible
QueuedTask.Run(() => Project.Current.AddItem(my_custom_project_item));
            
//To retrieve the given custom project item container itself...
var containerType = "MyCustomContainer";
var container = Project.Current.GetProjectItemContainer(containerType) as MyProjectItemContainer;
...etc.
Inheritance Hierarchy

System.Object
   ArcGIS.Desktop.Framework.Contracts.PropertyChangedBase
      ArcGIS.Desktop.Core.Item
            ArcGIS.Desktop.Core.CustomProjectItemContainer<T>

Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

CustomProjectItemContainer<T> Members
ArcGIS.Desktop.Core Namespace