Unity的Deferring the Resolution of Objects

Unity给出一种延迟创建对象的方案，可以先获取对象的创建器 -> 再注册类型 -> 其余代码 -> 创建类型实例，创建器的类型必须是Func<T>，而不是和Func相同返回值的delegate。看一个简单示例：

UnityContainer unityContainer = new UnityContainer();
unityContainer.LoadConfiguration();

Func<TextWriter> createFactory = unityContainer.Resolve<Func<TextWriter>>();

unityContainer.RegisterType<TextWriter, StringWriter>(new InjectionConstructor());

TextWriter textWriter = createFactory();

由于4.0默认新增了Lazy<T>（3.5可以添加并行库System.Threading.dll的引用），可以将类型的创建延迟，稍做修改后的代码：

IUnityContainer unityContainer = new UnityContainer();
unityContainer.LoadConfiguration();

Func<TextWriter> createFactory = unityContainer.Resolve<Func<TextWriter>>();

unityContainer.RegisterType<TextWriter, StringWriter>(new InjectionConstructor());

Lazy<TextWriter> textWriter = new Lazy<TextWriter>(createFactory);