COM 互操作接口转换
按照本文，我已成功将 C++ COM 类/接口声明转换为C# 像这样：
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid(IfaceGuid)]
public interface IFoo
{
void Bar();
}
[ComImport, Guid(ClassGuid)]
public class Foo
{ }
我这样使用它：
var foo = new Foo();
var ifoo = (IFoo)foo;
ifoo.Bar();
我的问题是，考虑到 Foo 没有实现 IFoo （即使在运行时，typeof(Foo).GetInterfaces() 为空）并且禁止用户定义的接口转换？
这是专门为 COM 保留的特殊处理吗？ C# 规范对此有何规定？
Following this article, I have successfully translated C++ COM class/interface declaration into C# like this:
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid(IfaceGuid)]
public interface IFoo
{
void Bar();
}
[ComImport, Guid(ClassGuid)]
public class Foo
{ }
I use it like this:
var foo = new Foo();
var ifoo = (IFoo)foo;
ifoo.Bar();
My question is, how can this possibly work, considering that Foo doesn't implement IFoo (even at runtime, typeof(Foo).GetInterfaces() is empty) and that user-defined conversions to interfaces are forbidden?
Is this some special handling reserved just for COM? What does the C# specification have to say about this?
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与“普通”.NET 类相比，ComImport 类型的处理方式有所不同，因为它们构成了底层 COM 组件类的运行时可调用包装器。将其中之一的实例转换为 COM 接口类型会透明地映射到对 COM 接口方法
IUnknown.QueryInterface的对象实现的调用。如果所请求接口的 QI 在 COM 级别成功，则 C# 转换也将成功。
ComImporttypes are treated differently compared to "normal" .NET classes, as they constitute a runtime-callable wrapper around an underlying COM coclass. Casting an instance of one of these into a COM interface type is transparently mapped into a call to the object's implementation of the COM interface methodIUnknown.QueryInterface.If QI for the requested interface succeeds at the COM level, then the C# cast will also succeed.
嗯，是的，将带有
ComImport标记的类转换为 COM 接口会在幕后产生QueryInterface()- 我猜这是在 RCW 内部完成的。这样，
new会导致CoCreateInstance()被调用，然后强制转换会导致QueryInterface()被调用。Well, yes, casts for classes marked with
ComImportto COM interfaces result in aQueryInterface()under the hood - that I guess is done inside the RCW.This way
newleads toCoCreateInstance()being called and then the cast leads toQueryInterface()being called.