c# - 如何使用非托管导出将函数指针从 C++ 发送到 C# dll 以用作回调

Question

我正在使用 Robert Giesecke 的非托管导出从我的 native C++ 应用程序调用我的 C# 托管 dll 中的函数。我现在需要以某种方式将函数指针从我的 C++ 应用程序传递到 C# dll，以便我的 dll 可以对 c++ 进行回调。这让我难住了。

C++

//Normal call to CSharp dll using Unmanaged Exports
FString UHostBridgeComponent::DoCallToCCsharp()
{

  FString filePath = FPaths::Combine(*FPaths::GamePluginsDir(), TEXT("ThirdParty"), TEXT("CSharp.dll")); 

  void *DLLHandle = NULL;
  if (FPaths::FileExists(filePath))
  {
    DLLHandle = FPlatformProcess::GetDllHandle(*filePath); // Retrieve the DLL.
  }
  if (DLLHandle != NULL)
  {
    _DoTest DLLFuncPtr = NULL;
    FString procName = "DoTest";
    DLLFuncPtr = (_DoTest)FPlatformProcess::GetDllExport(DLLHandle, *procName);
    if (DLLFuncPtr != NULL)
    {
        const char* result = DLLFuncPtr(false);
        FString output(result);
        return output;
    }
  }
  return "";
}

C#

    //Function called from C++ application
    [DllExport("DoTest", CallingConvention = CallingConvention.StdCall)]
    public static string DoTest(bool result)
    {

        //Do processing
        //...

        string result = "this is the result string";
        return result;
    }

我会想象在 C# 中调用函数时需要将指针传递给 C++ 中的函数。

const char * result = DLLFuncPtr(pointerToMyFunction);

该指针必须保存到 C# 中的变量，并在 C# dll 想要将数据发送到 C++ 应用程序时作为回调执行。

我不确定如何定义这些函数和变量。任何帮助将不胜感激。

Answer 1

我设法自己弄明白了。看下面的答案

C++

//Function pointer typedef
typedef bool(*functionPointer)(const char* data);

//the actual function that gets pointed to
bool UHostBridgeComponent::realFunction(const char * data)
{
    FString output(data);
    UE_LOG(LogEGM, Log, TEXT("CALLBACK FUNCTION data= %s"), *output);   
    return true;
}

//function pointer as variable (not yet pointing to realFunction)
functionPointer myFunc;

//function to call in C# that passes the function pointer
typedef bool(*_DoSendCallbackFunction)(functionPointer callback);

bool UHostBridgeComponent::DoCallbackTest()
{
    FString filePath = FPaths::Combine(*FPaths::GamePluginsDir(), TEXT("ThirdParty"), TEXT("CSharp.dll")); 

    void *DLLHandle = NULL;
    if (FPaths::FileExists(filePath))
    {
        DLLHandle = FPlatformProcess::GetDllHandle(*filePath);
    }
    if (DLLHandle != NULL)
    {       
        _DoSendCallbackFunction DLLFuncPtr = NULL;
        FString procName = "DoSendCallbackFunction";
        DLLFuncPtr = (_DoSendCallbackFunction)FPlatformProcess::GetDllExport(DLLHandle, *procName);
        if (DLLFuncPtr != NULL)
        {
          myFunc = &realFunction; //point myFunc to the function realFunction
          return DLLFuncPtr(myFunc);            
        }
    }
  return false;
}

C#

public delegate bool FooDelegate(string data);

    [DllExport("DoSendCallbackFunction", CallingConvention = CallingConvention.StdCall)]
    public static bool DoSendCallbackFunction(IntPtr callback)
    {
        FooDelegate myFooDelegate = (FooDelegate)Marshal.GetDelegateForFunctionPointer(callback,typeof(FooDelegate));
        string theString = "This is the data!!";
        myFooDelegate(theString);

        return true;
    }

结果被打印到我的日志文件中:

LogEGM: CALLBACK FUNCTION data= This is the data!!