Net Core 大量使用依赖注入(Dependency Inject), 打个比方,我们常用的日志组件有Log4Net,NLog等等.
如果我们要随时替换日志组件,那么代码中就不能直接引用某个组件的内容,也不能直接New 某个组件.
而是应该定义一组接口, 然后包装各个组件,实现这个接口. Net Core 自带组件容器, 启动程序时,指定接口对应的实现.
然后在各个Controller 里, 通过构造函数的参数,把要带过去的接口,把容器里的对象自动传过去
在cshtml view页面,要使用@inject方法, 例如在页面使用Session,就要@inject IHttpContextAccessor _httpContextAccessor
@inject CRM.PermissionLogic plogic
@inject IHttpContextAccessor _httpContextAccessor
@{int userid =(int)_httpContextAccessor.HttpContext.Session.GetInt32("UserId");}
如果要在静态类里使用,则要用到ServiceProvider, 在Startup.cs里注入,然后再用 serviceProvider.GetService<XXX>();
public void ConfigureServices(IServiceCollection services)
{
//注入
services.AddSingleton<IPageHeadBuilder, PageHeadBuilder>(); //解析依赖 对于一个服务A来说，它可能并不是独立的，它还在依赖服务B和服务C，而服务B又依赖服务D和服务E。。
//一个合格的容器得再我们需要服务A时，能够正确的解析这个依赖链，并按照正确的顺序实例化并返回服务A。
//ServiceProvider是ASP.NET Core团队提供的默认的依赖注入容器。
LayoutExtension.serviceProvider= services.BuildServiceProvider();
}
public static class LayoutExtension
{
public static IServiceProvider serviceProvider { get; set; } //定义一个IServiceProvider public static IPageHeadBuilder GetService()
{
return serviceProvider.GetService<IPageHeadBuilder>();
} public static void SetActiveMenuItemSystemName(this IHtmlHelper html, string systemName)
{
var head = GetService();
head.SetActiveMenuItemSystemName(systemName);
} public static string GetActiveMenuItemSystemName(this IHtmlHelper html)
{
var head = GetService();
return head.GetActiveMenuItemSystemName();
}
}
各个页面/Controller ,再调用接口的方法. 所谓的面向接口编程.
Net Core 在Microsoft.Extension.Logging定义了ILogger,ILoggerFactory,ILoggerProvider 这几个接口, 日志组件实现这个接口就可以被调用了.
上网查了一下,NLog已经实现了这些接口了,你用Nuget找NLog.Web.AspNetCore 就已经包装好了. 具体文档,请看这篇文章,非常详细.
https://github.com/NLog/NLog.Web/wiki/Getting-started-with-ASP.NET-Core-2
我们来看一下代码, 要调用NLog, 在Program.cs里
public static IWebHost BuildWebHost(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.ConfigureLogging((hostingContext, logging) =>
{
logging.AddConsole();
logging.AddDebug();
})
.UseNLog()
.Build();
}
调用NLog写Log, 在构造函数里增加参数,类型是接口,不能是实现类
using Microsoft.Extensions.Logging; public class HelloMiddleware
{
private readonly ILogger<HelloMiddleware> _logger;
private readonly RequestDelegate _next; public HelloMiddleware(RequestDelegate next,ILogger<HelloMiddleware> logger)
{
_next = next;
_logger = logger;
} public Task Invoke(HttpContext httpContext)
{
httpContext.Response.WriteAsync("Hello in Class Invoke"+ Environment.NewLine);
_logger.LogInformation("******hello middleware*********");
return _next(httpContext);
}
}
MVC的controller写法也类似
private readonly CRMContext _context;
private readonly IConfiguration _config;
private readonly ILogger<AccountController> _logger; public AccountController(CRMContext context
IConfiguration configuration,ILogger<AccountController> logger)
{
_context = context;
_config = configuration;
_logger = logger;
}
我们也可以把常用的注入(例如数据库 CRMContext context ) 放在基类BaseController, 子类的构造函数继承基类的构造函数
private readonly IConfiguration _config;
private readonly ILogger<AccountController> _logger; public AccountController(
IConfiguration configuration,ILogger<AccountController> logger):base(context)
{ _config = configuration;
_logger = logger;
}
public abstract class BaseController : Controller
{
protected readonly CRMContext _context; public BaseController(CRMContext context)
{
_context = context;
}
}
我们来看看UseNLog()这个方法的代码,看看做了什么
/// <summary>
/// Use NLog for Dependency Injected loggers.
/// </summary>
public static IWebHostBuilder UseNLog(this IWebHostBuilder builder)
{
return UseNLog(builder, null);
} /// <summary>
/// Use NLog for Dependency Injected loggers.
/// </summary>
/// <param name="builder"></param>
/// <param name="options">Options for logging to NLog with Dependency Injected loggers</param>
/// <returns></returns>
public static IWebHostBuilder UseNLog(this IWebHostBuilder builder, NLogAspNetCoreOptions options)
{
if (builder == null) throw new ArgumentNullException(nameof(builder));
options = options ?? NLogAspNetCoreOptions.Default; builder.ConfigureServices(services =>
{
//note: when registering ILoggerFactory, all non NLog stuff and stuff before this will be removed
services.AddSingleton<ILoggerProvider>(serviceProvider =>
{
ServiceLocator.ServiceProvider = serviceProvider;
return new NLogLoggerProvider(options);
}); //note: this one is called before services.AddSingleton<ILoggerFactory>
if (options.RegisterHttpContextAccessor)
{
services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
} RegisterHiddenAssembliesForCallSite();
});
return builder;
}
而Log4Net 就没有官方的包装,只有一个第三方包装的, 但包装的不好, 日志的配置不是放在Program.cs, 而是放在StartUp.cs. 我打算有时间再重新包装一次.
参考这篇文章
http://www.cnblogs.com/drivenwinder/p/8300881.html