Attach/Associate Workflow to Content Type SharePoint

  private bool CreateWorkflowAssociation(string strContentTypeName, string strWorkflowName, string strTaskList, string strHistoryList, string strSiteCollection)
        {
            SPSite objSite = null;
            SPWeb objWeb = null;
            SPContentType objContentType = null;
            bool blnReturn = false;

            try
            {
                objSite = new SPSite(strSiteCollection);
                objWeb = objSite.OpenWeb();

                objWeb.AllowUnsafeUpdates = true;
                objWeb.Update();
                objContentType = objWeb.ContentTypes[strContentTypeName];

                // Get the specific template for ReminderWorkflow
                SPWorkflowTemplate workflowTemplate = null;
                foreach (SPWorkflowTemplate template in objWeb.WorkflowTemplates)
                {
                    workflowTemplate = template;
                    if (workflowTemplate.Name == strWorkflowName)
                        break;
                }
                // Create an association.              
                SPWorkflowAssociation workflowAssociation = SPWorkflowAssociation.CreateWebContentTypeAssociation(workflowTemplate, strWorkflowName, strTaskList, strHistoryList);

                if (objContentType.WorkflowAssociations.GetAssociationByName(workflowAssociation.Name, objWeb.Locale) == null)
                    objContentType.WorkflowAssociations.Add(workflowAssociation);
                else
                    objContentType.WorkflowAssociations.Update(workflowAssociation);

                objWeb.Update();
                blnReturn = true;
                LogWindow.Text = "WORKFLOW ASSOCIATION DONE SUCCESSFULLY FOR " + strContentTypeName;
            }
            catch (Exception ex)
            {
                //throw;
                LogWindow.Text = "ERROR DETECTED WHILE WORKFLOW ASSOCIATION FOR " +" " + strContentTypeName +" " + ex.Message.ToString();
            }
            finally
            {
                if (objSite != null) objSite.Close();
                if (objWeb != null) objWeb.Close();
            }
            return (blnReturn);
        }


Usage:-


 bool AssociateWorkflow = CreateWorkflowAssociation(ContentType, "RetentionPolicy", "Tasks", "Workflow History", sitecollectionUrl);