MVC source code singleton pattern
Why does .net MVC source code ControllerBuilder use a delegate to assign the controller factory?:
private Func<IControllerFactory> _factoryThunk;
public void SetControllerFactory(IControllerFactory controllerFactory) {
_factoryThunk = () => controllerFactory;
}
W开发者_如何转开发hy can't it just assign the ControllerFactory directly?, ie:
private IControllerFactory _factory;
public void SetControllerFactory(IControllerFactory controllerFactory) {
_factory = controllerFactory;
}
public void SetControllerFactory(Type controllerFactoryType) {
_factory = (IControllerFactory)Activator.CreateInstance(controllerFactoryType);
}
The reason that _factoryThunk
is currently defined as a Func<IControllerFactory>
is that it's a generic means to support both overloads:
void SetControllerFactory(Type);
void SetControllerFactory(IControllerFactory);
The implementation of the first one uses the fact that _factoryThunk
is a Func
by declaring that Func
inline by using Activator
to instantiate the Type
lazily:
this._factoryThunk = delegate {
IControllerFactory factory;
try
{
factory = (IControllerFactory) Activator.CreateInstance(controllerFactoryType);
}
catch (Exception exception)
{
throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, MvcResources.ControllerBuilder_ErrorCreatingControllerFactory, new object[] { controllerFactoryType }), exception);
}
return factory;
};
Therefore, the reason the other overload looks like it has a spurious implementation is that since _factoryThunk
is declared as a Func
, the line you propose wouldn't have even compiled:
_factoryThunk = controllerFactory;
_factoryThunk
is a Func<IControllerFactory>
whereas controllerFactory
is an IControllerFactory
-- incompatible types.
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