其中之一是用于配置的依赖注入方法.似乎我必须通过一个参数通过堆栈.我可能误会某事或做错了.
想象一下,我有一个名为“contactEmailAddress”的配置属性.当订购新订单时,我将使用该配置属性发送电子邮件.考虑到这种情况,我的ASP.NET 5堆栈将如下所示：
Startup.cs
public class Startup
{
public IConfiguration Configuration { get; set; }
public Startup(IHostingEnvironment environment)
{
var configuration = new Configuration().AddJsonFile("config.json");
Configuration = configuration;
}
public void ConfigureServices(IServiceCollection services)
{
services.Configure<AppSettings>(Configuration.GetSubKey("AppSettings"));
services.AddMvc();
}
public void Configure(IApplicationBuilder app)
{
app.UseErrorPage();
app.UseMvc(routes =>
{
routes.MapRoute("default","{controller}/{action}/{id}",defaults: new { controller = "Home",action = "Index" });
}
);
app.UseWelcomePage();
}
AppSettings.cs
public class AppSettings
{
public string ContactEmailAddress { get; set; }
}
config.json
{
"AppSettings": {
"ContactEmailAddress":"support@mycompany.com"
}
}
OrderController.cs
[Route("orders")]
public class OrdersController : Controller
{
private IOptions<AppSettings> AppSettings { get; set; }
public OrdersController(IOptions<AppSettings> appSettings)
{
AppSettings = appSettings;
}
[HttpGet("new-order")]
public IActionResult OrderCreate()
{
var viewmodel = new Orderviewmodel();
return View(viewmodel);
}
[HttpPost("new-order")]
public IActionResult OrderCreate(Orderviewmodel viewmodel)
{
return new HttpStatusCodeResult(200);
}
}
Order.cs
public class Order()
{
public void Save(IOptions<AppSettings> appSettings)
{
// Send email to address in appSettings
}
public static List<Order> FindAll(IOptions<AppSettings> appSettings)
{
// Send report email to address in appSettings
return new List<Order>();
}
}
正如上面的例子所示,我将AppSettings传递给整个堆栈.这听起来不正确.为了进一步担忧,如果我尝试使用需要访问配置设置的第三方库,则此方法将无法正常工作.第三方库如何访问配置设置？我误会了吗？有没有更好的方法来做到这一点？
解决方法
AppSettings提供运行时访问应用程序特定的值,如UICulture字符串,联系人电子邮件等.
DI容器是管理对服务及其终生范围的访问的工厂.例如,如果MVC控制器需要访问您的EmailService,您将进行配置
public void ConfigureServices(IServiceCollection services)
{
// Add all dependencies needed by Mvc.
services.AddMvc();
// Add EmailService to the collection. When an instance is needed,// the framework injects this instance to the objects that needs it
services.AddSingleton<IEmailService,EmailService>();
}
然后,如果我们的家庭控制器需要访问您的EmailService,我们通过将它作为参数添加到Controller构造函数中来添加对它的接口的依赖
public class HomeController : Controller
{
private readonly IEmailService _emailService;
private readonly string _emailContact;
/// The framework will inject an instance of an IEmailService implementation.
public HomeController(IEmailService emailService)
{
_emailService = emailService;
_emailContact = System.Configuration.ConfigurationManager.
AppSettings.Get("ContactEmail");
}
[HttpPost]
public void EmailSupport([FromBody] string message)
{
if (!ModelState.IsValid)
{
Context.Response.StatusCode = 400;
}
else
{
_emailService.Send(_emailContact,message);
依赖注入的目的是管理服务的访问和使用寿命.
在上一个示例中,在我们的应用程序启动中,我们配置了DI Factory,将IEmailService的应用程序请求与EmailService相关联.所以当我们的控制器被MVC框架实例化时,框架注意到我们的家庭控制器期望IEmailService,框架检查我们的应用服务集合.它找到映射指令,并将一个Singleton EmailService(占位接口的后代)注入我们的主控制器.
超多形态因子 – 有恶心！
为什么这很重要？
如果您的联系人电子邮件更改,您更改AppSetting值并完成.来自ConfigurationManager的“ContactEmail”的所有请求都将全局更改.字符串很容易当我们可以只是哈希时,不需要注入.
如果您的存储库,电子邮件服务,日志记录服务等更改,您希望Global方式更改对此服务的所有引用.服务引用不像不可变字符串文字那样容易地传输.服务实例化应由工厂处理以配置服务的设置和依赖关系.
所以,在一年中你开发一个RobustMailService：
Class RobustMailService : IEmailService
{
....
}
只要您的新RobustMailService继承并实现了IEmailService接口,您可以通过更改以下方式替换全局邮件服务的所有引用：
public void ConfigureServices(IServiceCollection services)
{
// Add all dependencies needed by Mvc.
services.AddMvc();
// Add RobustMailService to the collection. When an instance is needed,// the framework injects this instance to the objects that needs it
services.AddSingleton<IEmailService,RobustMailService>();
}
