asp.net webapi如何对接口参数解密后再传给Action

public override void OnActionExecuting(HttpActionContext actionContext)
{
            //获取参数
            var Param = actionContext.ActionArguments["jsondata"].ToString();

            base.OnActionExecuting(actionContext);

}

命名空间using System.Web.Http.Controllers;using System.Web.Http.Filters;

其中ActionArguments只有get没有set