ASP.NET MVC进阶之路:深入理解Controller激活机制并使用Ioc容器创建对象

　　本文标题说是"深入理解Controller"其实有点“标题党”的味道了。本篇只会探讨"Controller"的激活机制,也就是如何创建Controller的并调用的。本篇不是讲解Controller底层相关知识,不过后期博文会对其进行介绍。

0X1 DefaultControllerFactory

　　DefaultControllerFactory对象可以说是Controller创建激活的一个重要类,在默认情况下(这里的默认情况指没有向MVC指定负责创建Controller的类)DefaultControllerFactory负责Controller的创建于激活。本文讨论的重点将会放在Controller的创建。

　　我们先看DefaultControllerFactory类的几个方法

  public virtual IController CreateController(RequestContext requestContext, string controllerName);
        public virtual void ReleaseController(IController controller);
        protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType);
        protected internal virtual SessionStateBehavior GetControllerSessionBehavior(RequestContext requestContext, Type controllerType);
        protected internal virtual Type GetControllerType(RequestContext requestContext, string controllerName);

　  我们可以看到CreateController方法,它主要的作用是“ 使用指定的请求上下文来创建指定的控制器”,也就是说其实是通过这个方法进行创建控制器的操作。我相信很多人看到这里的第一想法就是“虚方法重写不久完了吗“？别急,我们来看看CreateController的源代码：

public virtual IController CreateController(RequestContext requestContext, string controllerName)
{
    if (requestContext == null)
    {
        throw new ArgumentNullException("requestContext");
    }
    if (string.IsNullOrEmpty(controllerName) && !requestContext.RouteData.HasDirectRouteMatch())
    {
        throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
    }
    Type controllerType = this.GetControllerType(requestContext, controllerName);
    return this.GetControllerInstance(requestContext, controllerType);
}

　　我们可以看到CreateController方法在对参数进行验证后会调用其实例本身的GetControllerInstance方法,由这个方法最后来创建Controller的实例。

0X2 第一种实现方式

　　我们新建一个MVC应用,并新建一个名为NinjectController的类派生于DefaultControllerFactory,重写DefaultControllerFactory的GetControllerInstance方法,代码如下：

        private static IKernel _kernerl;
        public static IKernel Kernerl
        {
            get
            {
                if (_kernerl == null)
                    _kernerl = new StandardKernel();
                return _kernerl;
            }
        }

        static NinjectController()
        {
            //把Home绑定到Ninject里面
            Kernerl.Bind<HomeController>().To<HomeController>();
        }


        protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
        {
            if (Kernerl == null)
                throw new NotImplementedException("Kinject未绑定任何数据");
            if (controllerType == null || Kernerl.Get(controllerType) == null)
                return null;
            return (IController)Kernerl.Get(controllerType);
        }

　　这种方法虽然可以实现,但是在开发中并不可取,我们再来看第二种方式。

0X3 第二种实现方式

　　我们通过查看GetControllerInstance的源代码可以发现它最终调用了实例中ControllerActivator的Create方法进行创建Controller对象，ControllerActivator类型是一个IControllerActivator接口,那么这个ControllerActivator是在哪赋值的呢？我们看下DefaultControllerFactory的构造函数

public DefaultControllerFactory() : this(null, null, null)
{
}

public DefaultControllerFactory(IControllerActivator controllerActivator) : this(controllerActivator, null, null)
{
}

 　　DefaultControllerFactory有一个内部调用的方法,其源代码如下:

internal DefaultControllerFactory(IControllerActivator controllerActivator, IResolver<IControllerActivator> activatorResolver, IDependencyResolver dependencyResolver)
{
    if (controllerActivator != null)
    {
        this._controllerActivator = controllerActivator;
        return;
    }
    IResolver<IControllerActivator> arg_44_1 = activatorResolver;
    if (activatorResolver == null)
    {
        arg_44_1 = new SingleServiceResolver<IControllerActivator>(() => null, new DefaultControllerFactory.DefaultControllerActivator(dependencyResolver), "DefaultControllerFactory constructor");
    }
    this._activatorResolver = arg_44_1;
}

　　通过阅读源码我们可以看到当IControllerActivator等于Null的时候,则会通过  DefaultControllerFactory.DefaultControllerActivator方法来创建IControllerActivator对象,我们继续阅读DefaultControllerActivator的源代码

public IController Create(RequestContext requestContext, Type controllerType)
    {
        IController result;
        try
        {
            result = (IController)(this._resolverThunk().GetService(controllerType) ?? Activator.CreateInstance(controllerType));
        }
        catch (Exception innerException)
        {
            throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ErrorCreatingController, new object[]
            {
                controllerType
            }), innerException);
        }
        return result;
    }

　　IControllerActivator的Create方法在创建IController对象的时候会从this._resoverThunk的GetServer方法中获取,this._resoverThunk是IControllerActivator的局部变量,该变量存储一个返回值为IDependencyResolver的委托,其定义如下：

private Func<IDependencyResolver> _resolverThunk;

　　而对其赋值则来则与IControllerActivator的构造方法,其源代码如下：

public DefaultControllerActivator() : this(null)
    {
    }

    public DefaultControllerActivator(IDependencyResolver resolver)
    {
        if (resolver == null)
        {
            this._resolverThunk = (() => DependencyResolver.Current);
            return;
        }
        this._resolverThunk = (() => resolver);
    }

　　从以上代码可以看出,this._resoverThunk实则是通过DependencyResolver.Current进行赋值的,而创建IController对象则是通过 this._resolverThunk().GetService(controllerType)来获取的,通俗来讲,默认的Conteroller实则是通过IDependencyResolver接口的GetService方法进行创建的,相信看到这里的朋友心中已经有了答案。没错,我们第二种做法就是通过自定义IDependencyResolver来创建我们的Contorller。

　　相信很多朋友会问,IDependencyResolver接口在MVC中起到什么作用。IDependencyResolver定义如下：

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

　　一个获取单个类型的方法,一个获取多个对象的方法。有一个名为DependencyResolver的,它本身并不实现IDependencyResolver接口,所以它和IDependencyResolver没有任何关系。我们来看下DependencyResolver的定义。

　　从上述代码我们可以清楚知道默认情况下实际上是调用了DependencyResolver的Current返回了当前对象,然后进行了对象的创建,那我们要做的只要改变Current的值就可以了,但是,我们有没有办法呢？答案是肯定的,DependencyResolver定义了一个SetResolver的方法,我们看下源码：

public void InnerSetResolver(object commonServiceLocator)
{
    if (commonServiceLocator == null)
    {
        throw new ArgumentNullException("commonServiceLocator");
    }
    Type type = commonServiceLocator.GetType();
    MethodInfo method = type.GetMethod("GetInstance", new Type[]
    {
        typeof(Type)
    });
    MethodInfo method2 = type.GetMethod("GetAllInstances", new Type[]
    {
        typeof(Type)
    });
    if (method == null || method.ReturnType != typeof(object) || method2 == null || method2.ReturnType != typeof(IEnumerable<object>))
    {
        throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, MvcResources.DependencyResolver_DoesNotImplementICommonServiceLocator, new object[]
        {
            type.FullName
        }), "commonServiceLocator");
    }
    Func<Type, object> getService = (Func<Type, object>)Delegate.CreateDelegate(typeof(Func<Type, object>), commonServiceLocator, method);
    Func<Type, IEnumerable<object>> getServices = (Func<Type, IEnumerable<object>>)Delegate.CreateDelegate(typeof(Func<Type, IEnumerable<object>>), commonServiceLocator, method2);
    this.InnerSetResolver(new DependencyResolver.DelegateBasedDependencyResolver(getService, getServices));
}

　　该方法最终会将指定的对象复制给Current,我们新建一个类名为NinjectDependencyResolver并实现IDependencyResolver接口。我们在类中定一个Ninject的字段,并封装一个用来往Ninject中添加对象的方法,其代码如下：

public class NinjectDependencyResolver : IDependencyResolver
    {
        private IKernel Kerner;

        NinjectDependencyResolver()
        {
            Kerner = new StandardKernel();
        }

        public void Registet<To, Form>() where Form : To
        {
            Kerner.Bind<To>().To<Form>();
        }
        public object GetService(Type serviceType)
        {
            return Kerner.TryGet(serviceType);
        }

        public IEnumerable<object> GetServices(Type serviceType)
        {
            return Kerner.GetAll(serviceType);
        }
    }

　　如需使用我们自定义的NinjectDependencyResolver,我们需要在Global.asax中对其进行注册：

protected void Application_Start()
        {
            //其他操作
            NinjectDependencyResolver ninjectDependencyResolver = new NinjectDependencyResolver();
            ninjectDependencyResolver.Registet<Controller, Controllers.HomeController>();//这里的Controller应该是具体类型,这里这样写只是为了演示
            DependencyResolver.SetResolver(ninjectDependencyResolver);
        }

　　再次运行我们的程序,则会看到效果。