IAsyncResultFilter

1、新建类CustomAsyncResultFilterAttribute继承Attribute, IAsyncResultFilter

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Project6.Model;

namespace Project6.Utility.Filters
{
    public class CustomAsyncResultFilterAttribute : Attribute, IAsyncResultFilter
    {
        public CustomAsyncResultFilterAttribute()
        {
            Console.WriteLine("过滤器的构造函数被执行");
        }

        public async Task OnResultExecutionAsync(ResultExecutingContext context, ResultExecutionDelegate next)
        {
            if(context.Result is JsonResult)
            {
                JsonResult jsonResult = (JsonResult)context.Result;
                context.Result = new JsonResult(new AjaxResult()
                {
                    Success = true,
                    Message ="OK",
                    Data = jsonResult.Value
                });
            }

            await next.Invoke();
        }
    }
}

2、新建控制器CustomAsyncResultController

using Microsoft.AspNetCore.Mvc;
using Project6.Utility.Filters;

namespace Project6.Controllers
{
    public class CustomAsyncResultController : Controller
    {
        public  CustomAsyncResultController()
        {
            Console.WriteLine("控制器的构造函数被执行");
        }

        [CustomAsyncResultFilter]
        public IActionResult Index()
        {
            return Json(new
            {
                Id = 123,
                Name = "net"
            });
        }
    }
}

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。