(注:本文参照 NickChapsas的Attributes get a feature long-overdue in C# 11)
今天看一个泛型特性的例子,这个功能在C#11才受支持。
在asp.net core mvc中,可以给action添加filter,达到拦截作用,实现如下:
public class MyFilter : IAsyncActionFilter { public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next) { Console.WriteLine("Action前执行"); await next(); Console.WriteLine("Action后执行"); } }
使用方式,在Action上添加ServiceFilter特性即可,如下:
[ServiceFilter(typeof(MyFilter))] public IEnumerable<WeatherForecast> Get() { return Enumerable.Range(1, 5).Select(index => new WeatherForecast { Date = DateTime.Now.AddDays(index), TemperatureC = Random.Shared.Next(-20, 55), Summary = Summaries[Random.Shared.Next(Summaries.Length)] }) .ToArray(); }
在运行前记得把MyFilter注放到Service容器中:
builder.Services.AddScoped<MyFilter>();
为了支持C#11,在项目文件.csproj中,PropertyGroup中添加一行<LangVersion>preview</LangVersion>
<Project Sdk="Microsoft.NET.Sdk.Web"> <PropertyGroup> <TargetFramework>net7.0</TargetFramework> <Nullable>enable</Nullable> <ImplicitUsings>enable</ImplicitUsings> <LangVersion>preview</LangVersion> </PropertyGroup> <ItemGroup> <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="7.0.0-preview.4.22251.1" /> <PackageReference Include="Swashbuckle.AspNetCore" Version="6.3.1" /> </ItemGroup> </Project>
现在就可以定义一个继承IFilterFactory的特性类了,并且是泛型的。
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)] public class GSWFilterAttribute<TFilter> : Attribute, IFilterFactory, IOrderedFilter where TFilter : IAsyncActionFilter { public bool IsReusable { get; set; } public int Order { get; set; } public IFilterMetadata CreateInstance(IServiceProvider serviceProvider) { if (serviceProvider != null) { var filter = (IFilterMetadata)serviceProvider.GetRequiredService(typeof(TFilter)); if (filter is IFilterFactory filterFactory) { filter = filterFactory.CreateInstance(serviceProvider); } return filter; } else { throw new ArgumentNullException(nameof(serviceProvider)); } } }
使用时,直接把泛型类型放上就可以了,如下:
[GSWFilter<MyFilter>] public IEnumerable<WeatherForecast> Get() { return Enumerable.Range(1, 5).Select(index => new WeatherForecast { Date = DateTime.Now.AddDays(index), TemperatureC = Random.Shared.Next(-20, 55), Summary = Summaries[Random.Shared.Next(Summaries.Length)] }) .ToArray(); }
虽然两种方法实现的功能是一样的,但后一种看起来更优雅一些。同时说明一下,如果多个MyFilter功能的过滤器,可以增加Order属性,如下:
[GSWFilter<MyFilter1>(Order = 2)] [GSWFilter<MyFilter2>(Order = 1)] public IEnumerable<WeatherForecast> Get()想要更快更方便的了解相关知识,可以关注微信公众号
![](/i/l/?n=23&i=blog/1101861/202212/1101861-20221206013702458-429317207.png)
标签:重构,serviceProvider,Random,Next,filter,过滤器,Action,public From: https://www.cnblogs.com/axzxs2001/p/16954069.html