mvc源码解析(7)创建Controller对象

    在上一篇文章中我们获取到包含Controller所在的命名空间等信息的ControllerType对象之后，这篇就开始讲创建Controller对象。在DefaultControllerFactory中获取到ControllerType之后，紧接着就是创建Controller对象。

  Type controllerType = GetControllerType(requestContext, controllerName);
  IController controller = GetControllerInstance(requestContext, controllerType);

GetControllerInstance方法的实现如下：

protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType) {
            if (controllerType == null) {
                throw new HttpException(404,
                    String.Format(
                        CultureInfo.CurrentCulture,
                        MvcResources.DefaultControllerFactory_NoControllerFound,
                        requestContext.HttpContext.Request.Path));
            }
            if (!typeof(IController).IsAssignableFrom(controllerType)) {
                throw new ArgumentException(
                    String.Format(
                        CultureInfo.CurrentCulture,
                        MvcResources.DefaultControllerFactory_TypeDoesNotSubclassControllerBase,
                        controllerType),
                    "controllerType");
            }
            return ControllerActivator.Create(requestContext, controllerType);
        }

我们可以看到红色的代码就是返回创建好了的Controller对象，Create方法是属于接口IControllerActivator：该接口具体定义如下：

    public interface IControllerActivator {
        IController Create(RequestContext requestContext, Type controllerType);
    }

类DefaultControllerActivator实现了该接口，Cretae方法具体实现如下：

private class DefaultControllerActivator : IControllerActivator {

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);
                }
            }

}

红色的代码首先判断GetService方法返回的对象能否转换为IController对象，如果可以则直接返回Cotroller对象，如果不能则根据controllerType创建一个Controller对象返回。我们来看GetService方法的实现的是接口IDependencyResolver里面的方法，由类DelegateBasedDependencyResolver来实现，具体如下：

 public object GetService(Type type) {
                try {
                    return _getService.Invoke(type);
                }
                catch {
                    return null;
                }
            }

到了这里我们就明白了真正创建Controller对象的地方就在这里，这个方法涉及到的Invoke方法，我们不做详解。