接口如何以这种方式实例化 [英] How interface can be instantiate this way

问题描述

我从网址看到人们可以像这样实例化界面

from a url i saw people can instantiate interface like this way

class Program
{
    static void Main(string[] args)
    {
        var foo = new IFoo(1);
        foo.Do();
    }
}

[
    ComImport, 
    Guid("C906C002-B214-40d7-8941-F223868B39A5"), 
    CoClass(typeof(FooImpl))
]
public interface IFoo
{
    void Do();
}

public class FooImpl : IFoo
{
    private readonly int i;

    public FooImpl(int i)
    {
        this.i = i;
    }

    public void Do()
    {
        Console.WriteLine(i);   
    }
}

如何写这样的 var foo = new IFoo（1）; 寻找指导。谢谢

how it is possible to write like this var foo = new IFoo(1); looking for guidance. thanks

推荐答案

这就是COM的工作原理。您已将 FooImpl 声明为 IFoo 的coclass。 new IFoo（1）; 将编译为 new FooImpl（1）;

That's just how COM works. You've declared FooImpl to be IFoo's coclass. new IFoo(1); will be compiled to new FooImpl(1);

根据C＃规范的第17.5节， System.Runtime.InteropServices 命名空间下的属性可能会破坏所有规则。这是微软C＃实现的特定内容。

According to §17.5 of the C# specification, attributes under the System.Runtime.InteropServices namespace may break all the rules. This is specific to Microsoft's C# implementation.

Marc Gravell和Jon Skeet关于此的博客文章非常好：谁说你无法实例化界面？和伪造COM来欺骗C＃编译器

Marc Gravell and Jon Skeet have really good blog posts about this: Who says you can’t instantiate an interface? and Faking COM to fool the C# compiler

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