protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state)
{
  IController controller;
  IControllerFactory factory;
  ProcessRequestInit(httpContext, out controller, out factory);
 
  //其它操作
  //调用 controller.Execute方法
}
 
private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
{
  HttpContext currentContext = HttpContext.Current;
 
  //从路由获取controller名称
  string controllerName = RequestContext.RouteData.GetRequiredString("controller");
 
  //通过ControllerBuilder获取ControllerFactory，默认就是DefaultControllerFactory
  factory = ControllerBuilder.GetControllerFactory();
 
  //通过ControllerFactory获取Controller对象
  controller = factory.CreateController(RequestContext, controllerName);
}

public virtual IController CreateController(RequestContext requestContext, string controllerName)
{
  //获取Controller类型
  Type controllerType = GetControllerType(requestContext, controllerName);
 
  IController controller = GetControllerInstance(requestContext, controllerType);
  return controller;
}
 
protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType)
{
  return ControllerActivator.Create(requestContext, controllerType);
}

private class DefaultControllerActivator : IControllerActivator
{
  private Func<IDependencyResolver> _resolverThunk;
 
  public DefaultControllerActivator()
    : this(null)
  {
  }
 
  public DefaultControllerActivator(IDependencyResolver resolver)
  {
    if (resolver == null)
    {
      _resolverThunk = () => DependencyResolver.Current;
    }
    else
    {
      _resolverThunk = () => resolver;
    }
  }
 
  public IController Create(RequestContext requestContext, Type controllerType)
  {
    try
    {
      return (IController)(_resolverThunk().GetService(controllerType) "htmlcode">

public interface IDependencyResolver
{
  object GetService(Type serviceType);
  IEnumerable<object> GetServices(Type serviceType);
}


　　默认DependencyResolver.Current使用的是DefaultDependencyResolver类型，这里又和ControllerFactory和ControllerActivator的设计一样了，如果我们自定义，那么就使用，否则就使用默认的。DefaultDependencyResolver定义如下：


private class DefaultDependencyResolver : IDependencyResolver
{
  public object GetService(Type serviceType)
  {
    if (serviceType.IsInterface || serviceType.IsAbstract)
    {
      return null;
    }
 
    try
    {
      //如果Controller Type创建Controller实例对象
      return Activator.CreateInstance(serviceType);
    }
    catch
    {
      return null;
    }
  }
 
  public IEnumerable<object> GetServices(Type serviceType)
  {
    return Enumerable.Empty<object>();
  }
}



　　可以看到，MVC会将Controller对象的创建通过DependencyResolver完成。将对象的创建通过DependencyResolver完成的好处是可以降低对象间的耦合度；另外，通过实现IDependencyResolver接口，我们可以完全控制对象的创建过程，例如将对象的依赖关系转移到配置文件中等等。
　　通过上面我们还知道了有三种默认类型：DefaultControllerFactory、DefaultControllerActivator和DefaultDependencyResolver，分别对应三个接口：IControllerFactory、IControllerActivator、IDependencyResolver。它们的设计是类似的，都是提供给外部一个接口，如果外部自己实现了这个过程，那么就使用，否则用默认的。实际上这也是我们参与Controller激活过程的三种做法。
三、实现IDependencyResolver接口
　　接下来通过一个例子证明上面的过程。我们要实现的需求是通过实现IDependencyResolver接口，实现Controller构造函数注入服务。如：


public class HomeController : Controller
{      
  private IUserService _service;
  public HomeController(IUserService service)
  {
    _service = service;
  }
 
  public ActionResult Index()
  {
    return Content(_service.GetUserName());
  }
}




　　HomeController只依赖于IUserService接口，不依赖于具体对象。
　　接下来我们实现IDependencyResolver接口，依赖注入的实现方式有很多种，这里我们使用Unity。如下：


public class UnityDependencyResolver : IDependencyResolver
{
  public object GetService(Type serviceType)
  {
    if(serviceType == null)
    {
      throw new ArgumentNullException("serviceType");
    }      
    return (serviceType.IsClass && !serviceType.IsAbstract)
      || Ioc.IsRegistered(serviceType) "serviceType");
    }
    return (serviceType.IsClass && !serviceType.IsAbstract)
      || Ioc.IsRegistered(serviceType) "htmlcode">

public class Ioc
{
  private static IUnityContainer _container = new UnityContainer();
 
  public static void RegisterType<TFrom,TTo>()
    where TTo : TFrom
  {      
    _container.RegisterType<TFrom, TTo>();
  }
 
  public static object GetService(Type type)
  {            
    return _container.Resolve(type);
  }
 
  public static IEnumerable<object> GetServices(Type type)
  {
    return _container.ResolveAll(type);
  }
 
  public static bool IsRegistered(Type type)
  {
    return _container.IsRegistered(type);
  }
}



接着，在Application_Start方法中，注册Service和设置IocDependencyResolver:
Ioc.RegisterType<IUserService, UserService>();

DependencyResolver.SetResolver(new IocDependencyResolver());

　　运行就可以看到HomeController构造函数的IUserService就是UserService类型了。
四、总结
 　　实际上，上面的例子我们也可以用实现IControllerFactory或者IControllerActivator达到同样的目的，但使用IDependencyResolver会更简单一点，而且大部分的IOC框架都已经提供了这样的功能。例如上面UnityDependencyResolver根本不用自己定义，Unity for MVC 已经有这么一个类型了，直接使用即可。如果使用Autofac的话可以是：DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
以上就是本文的全部内容，希望对大家的学习有所帮助。