如何在C#中使用C ++ DLL导出的接口指针 [英] How to use interface pointer exported by C++ DLL in C#

问题描述

我有一个用C ++编写的DLL，它可以导出函数CreateRisk.该函数返回一个接口指针，如下所示:

I have a DLL written in C++, which exports a function CreateRisk. The function returns an interface pointer, as follows:

extern "C"
{
    __declspec(dllexport) IRisk* __stdcall CreateRisk()
    {
        return new  Risk();


    }
}

IRisk源自IUnknown，并具有自定义方法Calculate:

IRisk is derived from IUnknown and has a custom method Calculate:

class IRisk: public IUnknown                               
{
public:
    virtual int __stdcall Calculate(int i,double s) = 0;  
};

Risk类实现IRisk接口(此处省略了实现).

the class Risk implements IRisk interfaces (the implementation is omitted here).

我想要的是在c#中调用函数CreateRisk并获取对IRisk的引用.

What I want is to call the function CreateRisk in c# and obtain a reference to IRisk.

我在c#中定义了包装器接口

I defined a wrapper interface in c#

    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]        
    public interface IRisk
    {
        [PreserveSig]                                            
        int Calculate(int i,double s);
    }

然后我在C#中添加了一个dll条目

and I added a dll entry in C#

    [DllImport("Risk.dll")]
    extern static IntPtr CreateRisk();

我可以在C#中调用CreateRisk并获取IntPtr的值类型.有什么方法可以将IntPtr编组到c#IRisk接口，以便我可以在C#中调用Calculate方法?

I can call CreateRisk in C# and obtain a value type of IntPtr. Is there any way to marshal the IntPtr to the c# IRisk interface so that I can call the Calculate method in C#?

我已经尝试过Marshal.GetIUnknownForObjectInContext，Marshal.GetObjectForIUnknown，但无济于事.

I have tried Marshal.GetIUnknownForObjectInContext,Marshal.GetObjectForIUnknown, but to no avail.

我知道创建一个COM组件可以做到这一点.但是，COM组件需要在系统中注册.我想避免这些麻烦，并让C#直接使用C ++ dll导出的接口.

I know creating a COM component can do it. However, COM component needs to be registered with the system. I want to avoid those troubles and let C# use the interface exported by the C++ dll directly.

PS:

以下是我的Risk类实现:

The following is my Risk class implementation:

class IRisk : public IUnknown                               
{
public:
    virtual int __stdcall Calculate(int i,double y ) = 0;  
};

class Risk:public IRisk
{
    int count;
public:
    Risk();
    virtual int __stdcall Calculate( int i ,double y);
    virtual ULONG __stdcall AddRef();
    ULONG __stdcall Release();
    HRESULT __stdcall QueryInterface(const IID& riid,void **ppvObject);
};

Risk::Risk(){
    count=0;
}

ULONG __stdcall Risk::AddRef()
{
    return ++count;
}
ULONG __stdcall Risk::Release()
{
    return --count;
}
HRESULT __stdcall Risk::QueryInterface(const IID& riid,void **ppvObject) {
    *ppvObject=this;
    AddRef();
    return S_OK;
}
int __stdcall Risk::Calculate(int i ,double y) {
    return (int)(i+y);
}

推荐答案

以下方法将起作用:

[DllImport("Risk.dll")]
extern static IRiskAssessment CreateRisk();

您将需要在界面中添加GUID:

You will need to add a GUID to the interface:

[Guid("your GUID goes here")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]        
public interface IRiskAssessment
{
    [PreserveSig]                                            
    int Calculate(int i,double s);
}

显然，您需要在C#代码中使用与C ++代码中相同的GUID！

Obviously you need to use the same GUID in the C# code as was used in the C++ code!

更新

看您的C ++ COM对象实现，明显的错误是在QueryInterface中.您不能为所有GUID返回S_OK.仅为您实现的接口返回S_OK.返回其他的E_NOINTERFACE.

Looking at your C++ COM object implementation, the obvious fault is in QueryInterface. You must not return S_OK for all GUIDs. Only return S_OK for the interfaces you implement. Return E_NOINTERFACE for the others.

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