本篇主要讲述MVC处理请求时创建Controller和执行Action的完整过程。
创建Controller
先查看MvcHandler中处理请求的方法BeginProcessRequest:
protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state) { IController controller; IControllerFactory factory; ProcessRequestInit(httpContext, out controller, out factory); IAsyncController asyncController = controller as IAsyncController; if (asyncController != null) { …… } else { …… } }
再查看其中创建Controller的方法ProcessRequestInit
private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory) { HttpContext currentContext = HttpContext.Current; …… AddVersionHeader(httpContext); RemoveOptionalRoutingParameters(); string controllerName = RequestContext.RouteData.GetRequiredString("controller"); factory = ControllerBuilder.GetControllerFactory(); controller = factory.CreateController(RequestContext, controllerName); …… }
Controller通过ControllerBuilder属性的方法GetControllerFactory获取到ControllerFactory对象然后由ControllerFactory创建,ControllerBuilder属性定义如下。
internal ControllerBuilder ControllerBuilder { get { if (_controllerBuilder == null) { _controllerBuilder = ControllerBuilder.Current; } return _controllerBuilder; } set { _controllerBuilder = value; } }
可知ControllerBuilder默认使用ControllerBuilder.Current,查看ControllerBuilder类的代码:
public IControllerFactory GetControllerFactory() { return _serviceResolver.Current; } internal ControllerBuilder(IResolver<IControllerFactory> serviceResolver) { _serviceResolver = serviceResolver ?? new SingleServiceResolver<IControllerFactory>( () => _factoryThunk(),new DefaultControllerFactory { ControllerBuilder = this }, "ControllerBuilder.GetControllerFactory"); }
可知默认返回的ControllerFactory为DefaultControllerFactory(当然我们也可以注册默认的自定义的ControllerFactory),这里我们可继续查看DefaultControllerFactory
internal DefaultControllerFactory(……) { …… _activatorResolver = activatorResolver ?? new SingleServiceResolver<IControllerActivator>( () => null, new DefaultControllerActivator(dependencyResolver), "DefaultControllerFactory constructor"); } } private IControllerActivator ControllerActivator { get { if (_controllerActivator != null) { return _controllerActivator; } _controllerActivator = _activatorResolver.Current; return _controllerActivator; } } public virtual IController CreateController(RequestContext requestContext, string controllerName) { …… 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); }
可以看到最终Controller由DefaultControllerActivator来创建
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) ?? Activator.CreateInstance(controllerType)); } catch (Exception ex) { throw new InvalidOperationException( String.Format( CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ErrorCreatingController, controllerType), ex); } }
到此为止Controller就被创建出来了,这里我们看到了DependencyResolver.Current,这是MVC的默认注入容器,如果设置了容器,Controller的创建就可以通过容器(GetService)来完成了,如果未实现DependencyResolver或DependencyResolver未注册该Controller则通过反射来创建(使用Activator.CreateInstance,必须存在无参构造函数)。
Controller注入
下面来看对框架的第一个扩展也是最基本的扩展:为框架提供Ioc容器并注册Controller。对于Ioc容器的起源和作用这里就不多讲了。目前Ioc的思想已经普遍地应用于各种开发实践当中了,特别是企业应用开发中,Spring已经是Java开发事实上的基础框架。Asp.net Mvc也深受影响,虽然框架本身没有提供Ioc容器的实现,但是提供了很方便的扩展方式,通过扩展我们不仅可以使用容器管理自定义的对象,甚至可以将对象注入到Mvc框架当中(简单的比如对Controller的注入)。因为Mvc框架默认首先通过容器来获取对象,然后才是框架提供的方式(一般是一种默认实现),在以后的分析中可以看到许多的源码都可以证实这一点。
下面我们通过添加Autofac来实现依赖注入。
首先通过nuget添加Autofac和Autofac.Mvc5的引用。
在App_Start目录下添加Autofac的初始化类如下:
public class AutofacConfig { public static IDependencyResolver GeResolver() { var builder = new ContainerBuilder(); Registers(builder); builder.RegisterControllers(Assembly.GetExecutingAssembly()); return new AutofacDependencyResolver(builder.Build()); } private static void Registers(ContainerBuilder builder) { } }
然后在Global.asax的Application_Start方法中添加代码如下:
DependencyResolver.SetResolver(AutofacConfig.GeResolver());
这样我们就完成了依赖注入(目前只是Controller的注入,当然以后可以AutofacConfig 的Registers方法中把我们需要注入的对象注入到Autofac容器中)。关于依赖注入需要注意的主要有两点:一个是ContainerBuilder的扩展方法RegisterControllers,其参数类型为params Assembly[]可以传入一个或多个Assembly然后注册这些Assembly里的Controller,这样我们就可以将Controller放到不同的工程里;另一个是DependencyResolver.SetResolver,这样会替换掉默认的DependencyResolver实现,我们正是通过这样把Autofac容器作为了Mvc的容器从而完成依赖注入。
下面通过一个简单的例子说明Ioc容器的应用。首先创建一个简单的接口及其实现的类
public interface IIocTest { string Say(); } public class IocTest: IIocTest { public string Say() { return "IocTest"; } }
然后再HomeController中添加一个该接口的字段,并创建一个构造函数用于注入(AutoFac默认只支持构造函数注入,但也可以开启属性注入)。
private IIocTest iocTestInsatnce; public HomeController(IIocTest iocTest) { iocTestInsatnce = iocTest; }
然后再一个Action中调用接口方法,然后通过ViewBag(或其它方法)将其传到页面并显示,页面显示有多种方法,这里直接加到标题中:
public ActionResult Index() { ViewBag.iocSays = iocTestInsatnce.Say(); return View(); }
@{ ViewBag.Title = "Home Page"+ ViewBag.iocSays; }
然后运行程序,查看相应页面的标题,验证注入是否成功。
执行Action
创建好Controller之后我们再来看Controller是如何执行请求的。
首先看ControllerBase,这是所有Controller的基类,查看它的处理方法BeginExecuteCore。
protected virtual IAsyncResult BeginExecuteCore(AsyncCallback callback, object state) { …… try { string actionName = GetActionName(RouteData); IActionInvoker invoker = ActionInvoker; IAsyncActionInvoker asyncInvoker = invoker as IAsyncActionInvoker; if (asyncInvoker != null) { BeginInvokeDelegate<ExecuteCoreState> beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState, ExecuteCoreState innerState) { return innerState.AsyncInvoker.BeginInvokeAction(innerState.Controller.ControllerContext, innerState.ActionName, asyncCallback, asyncState); }; EndInvokeVoidDelegate<ExecuteCoreState> endDelegate = delegate(IAsyncResult asyncResult, ExecuteCoreState innerState) { if (!innerState.AsyncInvoker.EndInvokeAction(asyncResult)) { innerState.Controller.HandleUnknownAction(innerState.ActionName); } }; ExecuteCoreState executeState = new ExecuteCoreState() { Controller = this, AsyncInvoker = asyncInvoker, ActionName = actionName }; return AsyncResultWrapper.Begin(callback, state, beginDelegate, endDelegate, executeState, _executeCoreTag); } else { …… } } …… }
可以看到Action的执行通过ActionInvoker. BeginInvokeAction实现,ActionInvoker的获取方式如下:
protected virtual IActionInvoker CreateActionInvoker() { return Resolver.GetService<IAsyncActionInvoker>() ?? Resolver.GetService<IActionInvoker>() ?? new AsyncControllerActionInvoker(); }