即将离职，闲来无事回顾下MVC的源码，到了Controller创建这里，由于流程有点复杂，鉴于自己记性不太好，索性就记录一下吧，方便日后参照。
首先看MvcHandler：
public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
{
//...
private ControllerBuilder _controllerBuilder;
internal ControllerBuilder ControllerBuilder
{
get
{
if (_controllerBuilder == null)
{
_controllerBuilder = ControllerBuilder.Current;
}
return _controllerBuilder;
}
set { _controllerBuilder = value; }
}
//...
protected internal virtual void ProcessRequest(HttpContextBase httpContext)
{
IController controller;
IControllerFactory factory;
ProcessRequestInit(httpContext, out controller, out factory);
try
{
controller.Execute(RequestContext);
}
finally
{
factory.ReleaseController(controller);
}
} private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
{
// ...
// Get the controller type
string controllerName = RequestContext.RouteData.GetRequiredString("controller"); // Instantiate the controller and call Execute
factory = ControllerBuilder.GetControllerFactory();
controller = factory.CreateController(RequestContext, controllerName);
//...
}
}
简而言之，controller通过实现IControllerFactory的工厂的CreateController()方法创建，而该工厂通过ControllerBuilder.GetControllerFactory()获得，而ControllerBuilder通过ControllerBuilder类型的一个静态属性Current获得，显然Current是ControllerBuilder类型的一个单例。
那么来看看ControllerBuidler：
public class ControllerBuilder
{
private static ControllerBuilder _instance = new ControllerBuilder();
private Func<IControllerFactory> _factoryThunk = () => null;
private HashSet<string> _namespaces = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
private IResolver<IControllerFactory> _serviceResolver;
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;
}
//...
}
GetControllerFactory()方法返回一个IResolver<IControllerFactory>类型实例的Current属性，默认为SingleServiceResolver<IControllerFactory>类型。
以下是SingleServiceResolver<IControllerFactory>的部分实现：
internal class SingleServiceResolver<TService> : IResolver<TService>
where TService : class
{
private Lazy<TService> _currentValueFromResolver;
private Func<TService> _currentValueThunk;
private TService _defaultValue;
private Func<IDependencyResolver> _resolverThunk;
private string _callerMethodName; public SingleServiceResolver(Func<TService> currentValueThunk, TService defaultValue, string callerMethodName)
{
_resolverThunk = () => DependencyResolver.Current;
_currentValueFromResolver = new Lazy<TService>(GetValueFromResolver);
_currentValueThunk = currentValueThunk;
_defaultValue = defaultValue;
_callerMethodName = callerMethodName;
} internal SingleServiceResolver(Func<TService> staticAccessor, TService defaultValue, IDependencyResolver resolver, string callerMethodName)
: this(staticAccessor, defaultValue, callerMethodName)
{
if (resolver != null)
{
_resolverThunk = () => resolver;
}
} public TService Current
{
get { return _currentValueFromResolver.Value ?? _currentValueThunk() ?? _defaultValue; }
} private TService GetValueFromResolver()
{
TService result = _resolverThunk().GetService<TService>(); if (result != null && _currentValueThunk() != null)
{
return result;
}
}
由此可见Current属性返回的值有一个优先级:
优先级最低的是_defaultValue,_defaultValue在构造函数中通过参数传递进来，在之前的CotrollerBuilder中可以看到，这个默认值是一个DefaultFactory类型实例；
次优先级的是对_currentValueThunk委托的调用，也在构造函数中作为参数传递进来，默认返回Null，并且可以通过CotrollerBuilder的SetControllerFactory()方法进行设置；
最高优先级的是一个GetValueFromResolver()方法的返回值，并通过Lazy<>实现延迟执行，GetValueFromResolver()方法内部，首先是对_resolverThunk委托的调用，该委托可通过构造函数的参数传递，否则返回一个DependencyResolver的Current属性，DependencyResolver我们就比较熟悉了，它用于IOC容器的设置和构建，关于它篇幅所限在后面详解吧，该属性返回一个IDependencyResolver类型实例，默认为MVC内部的一个IOC容器DefaultDependencyResolver，由于默认TService类型是一个接口类型，所以DefaultDependencyResolver的GetService()方法默认返回Null。
ControllerFactory的整个创建过程就是这样了。