This post is a contribution from Himani Sharma, an engineer with the SharePoint Developer Support team.
You have a workflow custom action that you’d like to be used in SharePoint 2010 workflow. This activity uses Microsoft.SharePoint.WorkflowActions.WorkflowContext to obtain WorkflowContext and hence use the workflow instance specific properties like ItemId, ListId, TaskListGuid, WorkflowInstanceId etc.,
In order to use this workflow custom action in SharePoint designer workflow, we create a custom workflow actions file. The WorkflowContext parameter expected by the custom action is passed like this: