asp.net mvc源码分析-Controllerl篇 如何创建Controller实例
在上一篇文章asp.net mvc源码分析-路由篇 如何找到 IHttpHandler中最后提到了MvcHandler，来上我们看看它的定义
public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
它有几个比较重要的属性：
internal ControllerBuilder ControllerBuilder ，ControllerBuilder 类主要负责创建IControllerFactory
public RequestContext RequestContext，RequestContext是对这次请求的HttpContext（httpContext类）和RouteData的包装
而它的BeginProcessRequest方法中有几句比较重要的代码：
IControllerFactory factory;
ProcessRequestInit(httpContext, out controller, out factory);
IAsyncController asyncController = controller as IAsyncController;
if (asyncController != null) {
}
else
{
Action action = delegate {
try {
controller.Execute(RequestContext);
}
finally {
factory.ReleaseController(controller);
}
return AsyncResultWrapper.BeginSynchronous(callback, state, action, _processRequestTag);
}
在这篇文章中我们主要关心ProcessRequestInit(httpContext, out controller, out factory); 如何创建controller
ProcessRequestInit方法大致如下：
private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory) {
string controllerName = RequestContext.RouteData.GetRequiredString("controller");
factory = ControllerBuilder.GetControllerFactory();
controller = factory.CreateController(RequestContext, controllerName);
}
string controllerName = RequestContext.RouteData.GetRequiredString("controller");这句很简单获取Controller的名称，RouteData是当前路由数据，里面的key包括我们注册是的url格式 "{controller}/{action}/{id}", 和默认的defaults=new { controller = "Home", action = "Index", id = UrlParameter.Optional }
现在大家知道为什么了我上一篇文章提到{controller}/{action}是必须得了吧。
现在让我们来看看ControllerBuilder的主要代码：
public ControllerBuilder() : this(null) { } internal ControllerBuilder(IResolver<IControllerFactory> serviceResolver) { _serviceResolver = serviceResolver ?? new SingleServiceResolver<IControllerFactory>( () => _factoryThunk(), new DefaultControllerFactory { ControllerBuilder = this }, "ControllerBuilder.GetControllerFactory" ); } public static ControllerBuilder Current { get { return _instance; } } public IControllerFactory GetControllerFactory() { return _serviceResolver.Current; } public void SetControllerFactory(IControllerFactory controllerFactory) { if (controllerFactory == null) { throw new ArgumentNullException("controllerFactory"); } _factoryThunk = () => controllerFactory; } public void SetControllerFactory(Type controllerFactoryType) { if (controllerFactoryType == null) { throw new ArgumentNullException("controllerFactoryType"); } if (!typeof(IControllerFactory).IsAssignableFrom(controllerFactoryType)) { throw new ArgumentException( String.Format( CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_MissingIControllerFactory, controllerFactoryType), "controllerFactoryType"); } _factoryThunk = delegate() { try { return (IControllerFactory)Activator.CreateInstance(controllerFactoryType); } catch (Exception ex) { throw new InvalidOperationException( String.Format( CultureInfo.CurrentCulture, MvcResources.ControllerBuilder_ErrorCreatingControllerFactory, controllerFactoryType), ex); } }; }由以上代码我们可以知道如果没有调用ControllerBuilder的SetControllerFactory方法那我们就用默认的DefaultControllerFactory，如果设置了我们就可以用我们自己ControllerFactory。如果项目有需要实现自己的ControllerFactory，那么我们可以Global.asax.cs的 protected void Application_Start()方法调用 ControllerBuilder.Current.SetControllerFactory(xxx); 让我们来看看DefaultControllerFactory是怎么创建的：
internal DefaultControllerFactory(IControllerActivator controllerActivator, IResolver<IControllerActivator> activatorResolver, IDependencyResolver dependencyResolver) {
if (controllerActivator != null) {
_controllerActivator = controllerActivator;
}
else {
_activatorResolver = activatorResolver ?? new SingleServiceResolver<IControllerActivator>(
() => null,
new DefaultControllerActivator(dependencyResolver),
"DefaultControllerFactory contstructor"
);
}
}
这里我们涉及到一个IControllerActivator接口，默认情况下用的是DefaultControllerActivator类，
现在我们已经得到了ControllerFactory，再看看它是怎么创建Controller的，说白了就是DefaultControllerFactory的CreateController方法
public virtual IController CreateController(RequestContext requestContext, string controllerName) {
。。
Type controllerType = GetControllerType(requestContext, controllerName);
IController controller = GetControllerInstance(requestContext, controllerType);
return controller;
}
默认我们是没有namespaces，而GetControllerType(requestContext, controllerName)主要是调用 GetControllerTypeWithinNamespaces(requestContext.RouteData.Route, controllerName, null /* namespaces */)
private class DefaultControllerActivator : IControllerActivator { 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) ?? Activator.CreateInstance(controllerType)); } catch (Exception ex) { throw new InvalidOperationException( String.Format( CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ErrorCreatingController, controllerType), ex); } } }这里的_resolverThunk()来源于DependencyResolver.Current，private static DependencyResolver _instance = new DependencyResolver();
public static IDependencyResolver Current {
get {
return _instance.InnerCurrent;
}
}
private IDependencyResolver _current = new DefaultDependencyResolver();
public IDependencyResolver InnerCurrent {
get {
return _current;
}
}
所以真正创建controller是在DefaultDependencyResolver的GetService方法，核心代码 return Activator.CreateInstance(serviceType);
这篇文件扯得比较远，可见创建Controller是多么的麻烦啊。阅读源代码主要是让我们理解其逻辑，同时也让我们学习其开发的思想。
本文讲的这么多，在项目中最常用的就是ControllerBuilder.Current.SetControllerFactory(xxx); 只要大家理解了它就可以了。