当我们进行项目开发时，往往在开发过程中需要临时加入一些常用功能性代码，如身份验证、日志记录、异常获取等功能。如果每个方法中都加入这些功能性代码的话，无疑使项目显得过于臃肿，代码繁杂。这时候就要加入过滤器了。.net framework及.net core中都支持非常简单的过滤器操作：Filter。它能在函数执行前或执行后切入函数。而不需要修改原来的代码，使项目更加清晰。
下面讲解Filter在.net core MVC中的用法。
首先，新建.net core mvc web应用程序，然后加入MyFilter类，继承ActionFilterAttribute
public class MyFilter : ActionFilterAttribute ???{ ???????public string Message { get; set; } ???????public override void OnActionExecuting(ActionExecutingContext filterContext) ???????{ ???????????base.OnActionExecuting(filterContext); ???????????filterContext.HttpContext.Response.Write("<br />" + "执行OnActionExecuting：" + Message + "<br />"); ???????} ???????public override void OnActionExecuted(ActionExecutedContext filterContext) ???????{ ???????????base.OnActionExecuted(filterContext); ???????????filterContext.HttpContext.Response.Write("<br />"+ "执行OnActionExecuted：" + Message + "<br />"); ???????} ???????public override void OnResultExecuting(ResultExecutingContext filterContext) ???????{ ???????????base.OnResultExecuting(filterContext); ???????????filterContext.HttpContext.Response.Write("<br />" + "执行OnResultExecuting：" + Message + "<br />"); ???????} ???????public override void OnResultExecuted(ResultExecutedContext filterContext) ???????{ ???????????base.OnResultExecuted(filterContext); ???????????filterContext.HttpContext.Response.Write("<br />" + "执行OnResultExecuted：" + Message + "<br />"); ???????} ???}然后在Home控制器中的Action中加入过滤器
public class HomeController : Controller ???{ ???????[MyFilter(Message ="首页")] ???????public ActionResult Index() ???????{ ???????????return Content("<br />" + "执行Index中的内容"+ "<br />"); ???????} ???????[MyFilter(Message = "关于页面")] ???????public ActionResult About() ???????{ ???????????return Content("<br />" + "执行About中的内容" + "<br />"); ???????} ???}这时候运行项目：/Home/Index,打印出如下内容：
运行/Home/About,打印出如下内容：
由此可以发现：执行循序是：OnActionExecuting>OnActionExecuted>OnResultExecuting>Action>OnResultExecuted
(Action执行之前执行OnActionExecuting，Action执行之后执行OnActionExecuted，Action返回之前执行OnResultExecuting，Action返回之后执行OnResultExecuted)
.net core AOP之Filter
原文地址：https://www.cnblogs.com/ontheroute/p/9113976.html