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        Dim allActivities As List(Of Activity) = WorkflowUtils.GetAllActivities(_workflowDefinition)

When creating a subclass overrule the abstract PerformLoad function to load the workflow. Use the GetService function to retreive a IDesignerHost reference and use its Container object to add all the workflow activities to the designer surface. See the WorkflowUtils GetAllActivities function for an easy way to get a reference to all nested activities.