Forum Post: How do I get WorkFlowActivityBase class?

I am creating a custom workflow in Microsoft Dynamics CRM to automatically update a field when a record is saved. A developer on a forum provided the following source code; but he has not responded to my questions. I am trying to get the code to compile on my machine. I installed the following NuGet packages, which resolved most of the errors: Microsoft.Xrm.Sdk.Workflow.2015 Microsoft.Xrm.Sdk.2015 But my project cannot resolve the WorkFlowActivityBase class. Is there a reference I should set or a NuGet package I should install to resolve this? Thank you. public class SalesRepActivity2 : WorkFlowActivityBase { [Input("Sales Rep Name")] public InArgument SalesRepName { get; set; } [Output("Sales Rep")] [ReferenceTarget("systemuser")] public OutArgument SalesRep { get; set; } [Output("IsSuccess")] public OutArgument IsSuccess { get; set; } [Output("Message")] public OutArgument Message { get; set; } protected override void Execute( CodeActivityContext activityContext, IWorkflowContext workflowContext, IOrganizationService CrmService, ITracingService trace) { try { string salesRepName = SalesRepName.Get(activityContext); if (string.IsNullOrWhiteSpace(salesRepName)) { IsSuccess.Set(activityContext, false); Message.Set(activityContext, "Sales Rep Name not provided"); } var QEsystemuser = new QueryExpression("systemuser"); QEsystemuser.ColumnSet.AddColumns("salesrepname"); QEsystemuser.Criteria.AddCondition("salesrepname", ConditionOperator.Equal, salesRepName); var results = CrmService.RetrieveMultiple(QEsystemuser); if (results == null || !results.Entities.Any()) { IsSuccess.Set(activityContext, false); Message.Set(activityContext, "User with " + salesRepName + " not found"); return; } if (results.Entities.Count > 1) { IsSuccess.Set(activityContext, false); Message.Set(activityContext, "Multiple users found with same name : " + salesRepName); return; } IsSuccess.Set(activityContext, true); SalesRep.Set(activityContext, results.Entities.Single().ToEntityReference()); } catch (Exception ex) { IsSuccess.Set(activityContext, false); Message.Set(activityContext, "An error occurred trying to find user : " + ex.Message); } }