ArcGIS Pro 2.8 API Reference Guide
OnCreateHtmlContent Method
Example 

ArcGIS.Desktop.Mapping Namespace > PopupContent Class : OnCreateHtmlContent Method
Occurs the first time the content for the item is requested. This method is only called if the IsDynamicContent property is true.
Syntax
protected internal virtual Task<string> OnCreateHtmlContent()
Protected Friend Overridable Function OnCreateHtmlContent() As Task(Of String)

Return Value

The html content to display in the pop-up.
Example
Show a custom pop-up with dynamically generated content.
public void ShowDynamicPopup(MapMember mapMember, List<long> objectIDs)
{
  //Get the active map view.
  var mapView = MapView.Active;
  if (mapView == null)
    return;

  //Create popup whose content is created the first time the item is requested.
  var popups = new List<PopupContent>();
  foreach (var id in objectIDs)
  {
    popups.Add(new DynamicPopupContent(mapMember, id));
  }
  
  mapView.ShowCustomPopup(popups);
}

internal class DynamicPopupContent : PopupContent
{
  public DynamicPopupContent(MapMember mapMember, long objectID)
  {
    MapMember = mapMember;
    ID = objectID;
    IsDynamicContent = true;
  }
  
  //Called when the pop-up is loaded in the window.
  protected override Task<string> OnCreateHtmlContent()
  {
    return QueuedTask.Run(() => string.Format("<b>Map Member: {0}, ID: {1}</b>", MapMember, ID));
  }
}
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

PopupContent Class
PopupContent Members