订阅活动类型的事件，然后在回调方法里面进行活动变量的读取或者操作。

//run a process instance to next step

IWorkflowService wfService = new WorkflowService();

var wfResult = wfService.CreateRunner(runner.UserID, runner.UserName)

         .UseApp(runner.AppInstanceID, runner.AppName, runner.AppInstanceCode)

         .UseProcess(runner.ProcessGUID, runner.Version)

         .NextStep(runner.NextActivityPerformers)

         .IfCondition(runner.Conditions)        //condition on the transiton

         .Subscribe(EventFireTypeEnum.OnActivityExecuting, (delegateContext, delegateService) => {

               if (delegateContext.ActivityCode == "Task1")

               {

                 delegateService.SaveVariable(ProcessVariableTypeEnum.Process, "name", "book-task1");

                 delegateService.SaveVariable(ProcessVariableTypeEnum.Process, "amount", "50");

                }

                return true;

          })   

      .Run();