1、新建类CustomAsyncResultFilterAttribute继承Attribute, IAsyncResultFilter

 1 using Microsoft.AspNetCore.Mvc;
 2 using Microsoft.AspNetCore.Mvc.Filters;
 3 using Project6.Model;
 4 
 5 namespace Project6.Utility.Filters
 6 {
 7     public class CustomAsyncResultFilterAttribute : Attribute, IAsyncResultFilter
 8     {
 9         public CustomAsyncResultFilterAttribute()
10         {
11             Console.WriteLine("过滤器的构造函数被执行");
12         }
13 
14         public async Task OnResultExecutionAsync(ResultExecutingContext context, ResultExecutionDelegate next)
15         {
16             if(context.Result is JsonResult)
17             {
18                 JsonResult jsonResult = (JsonResult)context.Result;
19                 context.Result = new JsonResult(new AjaxResult()
20                 {
21                     Success = true,
22                     Message ="OK",
23                     Data = jsonResult.Value
24                 });
25             }
26 
27             await next.Invoke();
28         }
29     }
30 }

2、新建控制器CustomAsyncResultController

 1 using Microsoft.AspNetCore.Mvc;
 2 using Project6.Utility.Filters;
 3 
 4 namespace Project6.Controllers
 5 {
 6     public class CustomAsyncResultController : Controller
 7     {
 8         public  CustomAsyncResultController()
 9         {
10             Console.WriteLine("控制器的构造函数被执行");
11         }
12 
13         [CustomAsyncResultFilter]
14         public IActionResult Index()
15         {
16             return Json(new
17             {
18                 Id = 123,
19                 Name = "net"
20             });
21         }
22     }
23 }

3、在各个方法开始处设置断点，运行/CustomAsyncResult

可以发现程序刚运行的时候会执行CustomAsyncResultFilterAttribute的构造方法，只执行一次，后面程序的执行顺序是

CustomAsyncResultController的构造方法-->

CustomAsyncResultController的Action方法-->

CustomAsyncResultFilterAttribute的OnResultExecutionAsync方法

输出结果为

{"success":true,"message":"OK","data":{"id":123,"name":"net"}}

在输出结果前，通过OnResultExecutionAsync方法，可以地结果进行修饰然后在输出。