IExceptionFilter、IAsyncExceptionFilter

IExceptionFilter在它的作用范围内，当程序发生异常，可以接收到异常，对异常进行统一的处理。

当程序同时继承了IExceptionFilter,IAsyncExceptionFilter，则优先处理异步方法OnExceptionAsync

1、新建过滤器类CustomExceptionFilterAttribute继承Attribute, IExceptionFilter

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.ViewFeatures;

namespace Project6.Utility.Filters
{
    public class CustomExceptionFilterAttribute : Attribute, IExceptionFilter
    {
        private readonly IModelMetadataProvider _IModelMetadataProvider;
        public CustomExceptionFilterAttribute(IModelMetadataProvider modelMetadataProvider)
        {
            _IModelMetadataProvider= modelMetadataProvider;
        }

        public void OnException(ExceptionContext context)
        {
           
            if(IsAjaxRequest(context.HttpContext.Request))  //判断是否是Ajax异步请求，返回一个JSON
            {
                context.Result = new JsonResult(new
                {
                    Sucess = false,
                    Message = context.Exception.Message
                });
            }
            else  //返回页面
            {
                ViewResult result = new ViewResult { ViewName="~/Views/Shared/Error.cshtml"};
                result.ViewData = new ViewDataDictionary(_IModelMetadataProvider, context.ModelState);
                result.ViewData.Add("Exception", context.Exception);
                context.Result = result;  //赋值给Result程序就不在往后执行了
            }
        }

        //public Task OnExceptionAsync(ExceptionContext context)
        //{
        //    throw new NotImplementedException();
        //}

        private bool IsAjaxRequest(HttpRequest request)
        {
            string header = request.Headers["X-Requested-With"];
            return "XMLHttpRequest".Equals(header);
        }
    }
}

2、新建控制器CustomExceptionFilterController

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

namespace Project6.Controllers
{
    public class CustomExceptionFilterController : Controller
    {
        [TypeFilter(typeof(CustomExceptionFilterAttribute))]
        public IActionResult Index()
        {
            throw new Exception("抛出个异常测试");
        }
    }
}

3、修改/Views/Shared/Error.cshtml

@model ErrorViewModel
@{
    ViewData["Title"] = "Error";
    Exception exception = ViewData["Exception"] as Exception;
}

<h1 class="text-danger">Error.</h1>
@if(exception != null){
    <h1>@exception.Message</h1>
}

4、执行程序/CustomExceptionFilter

可以发现当程序抛出异常，会进入CustomExceptionFilterAttribute-->OnException，在OnException里面做统一处理。返回异常结果。

5、IExceptionFilter的作用范围

　　a、action出现没有处理的异常

　　b、Service层出现的异常，因为异常是从下往上抛出，Service属于下层

　　c、构造器函数出现的异常

 

6、IExceptionFilter捕捉不到的异常

　　a、Action里面已经有try\catch捕捉异常，则不会在进入IExceptionFilter

　　b、View视图层抛出的异常

　　c、不存在的URL，404捕捉不到

　　d、其它Filter中出现的异常，有的能捕捉到，有的不能，比如IResourceFilter捕捉不到。