Subscribe to the event of the activity type, and then read or operate the activity variables in the callback method.

//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();