ASP.NET CORE MVC 2.0 如何在Filter中使用依赖注入来读取AppSettings

问：

ASP.NET CORE MVC 如何在Filter中使用依赖注入来读取AppSettings

答:

Dependency injection is possible in filters as well.

Here is a simple way to get connection string

public class EBisUserAuthResourceFilter : Attribute, IResourceFilter
{private readonly string connectionString;public EBisUserAuthResourceFilter(IConfiguration configuration){this.connectionString = configuration.GetSection("ConnectionStrings:DefaultConnection").Value;}public void OnResourceExecuted(ResourceExecutedContext context){// use this.connectionString
    }public void OnResourceExecuting(ResourceExecutingContext context){// use this.connectionString
    }
}

Now you can use this filter

[ServiceFilter(typeof(EBisUserAuthResourceFilter))]
public class HomeController : Controller
{  }

You also need to add this Filter to the service collection

public void ConfigureServices(IServiceCollection services)
{services.AddScoped<EBisUserAuthResourceFilter>();// your existing code to add other services
}

Another solution is to have a class representing the structure of the content of AppSettings.json file or a sub section and load that in your Startup classes' ConfigureServices method

services.Configure<SiteSettings>(Configuration);

and now you can inject IOptions<SiteSettings> in the constructor of your filter and use the needed property values. I prefer this as it is less magic strings in my code.

public class EBisUserAuthResourceFilter : Attribute, IResourceFilter
{private readonly string connectionString;public EBisUserAuthResourceFilter(IOptions<SiteSettings> settings){this.connectionString = settings.Value.connectionString ;}public void OnResourceExecuted(ResourceExecutedContext context){// use this.connectionString
    }public void OnResourceExecuting(ResourceExecutingContext context){// use this.connectionString
    }
}

原文链接

补充：

当然还有个更简单的办法，就是在Filter里面直接通过.Net Core App的方式来读取AppSettings的值，这个方法是最灵活的:

appsettings.json

{"Logging": {"IncludeScopes": false,"LogLevel": {"Default": "Warning"}},"AppSettings": {"CacheTimeSpan": 1200,"MD5PrivateKey": "KOPX&VDtt!890912hjk","Auth_UserName": "Username","Auth_Token": "Token"}
}

构造一个AppSettings类来反序列化appsettings.json文件中AppSettings节点下的内容：

public class AppSettings
{public int CacheTimeSpan { get; set; }public string MD5PrivateKey { get; set; }public string Auth_UserName { get; set; }public string Auth_Token { get; set; }
}

在Filter的构造函数中，构造AppSettings并读取其值：

public class AuthenticationFilterAttribute : Attribute, IAuthorizationFilter
{public AuthenticationFilterAttribute(){var builder = new ConfigurationBuilder().SetBasePath(Directory.GetCurrentDirectory()).AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);IConfigurationRoot configuration = builder.Build();var appSettings=configuration.GetSection("AppSettings").Get<AppSettings>();int cacheTimeSpanValue = appSettings.CacheTimeSpan;}public void OnAuthorization(AuthorizationFilterContext context){}
}

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