Component developers create and expose custom events by using the EventInfos collection. The collection is provided to the component by the data flow task. Custom events are first created, or defined, by calling the Add method. The custom event is raised during package execution by calling the FireCustomEvent method of the ComponentMetaData.
If you specify true in the AllowEventHandlers parameter when calling Add, the Event Handlers tab in SSIS Designer, in SQL Server Data Tools (SSDT), shows the custom event in the Event Handler drop down box.