如何使用非托管導出從C ++發送函數指針到C＃dll以用作回調

Question

我正在使用Robert Giesecke的Unmanaged Exports從我的本機C ++應用程序中調用C＃managed dll中的函數。 我現在需要以某種方式將函數指針從我的C ++應用程序傳遞給C＃dll，以便我的dll可以回調到c ++。 這讓我很難過。

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;
    }

我想在C＃中調用一個函數時，我需要在C ++中傳遞一個指向函數的指針。

const char * result = DLLFuncPtr(pointerToMyFunction);

該指針必須保存到C＃中的變量中，並在C＃dll想要將數據發送到c ++應用程序時作為回調執行。

我不確定如何定義這些函數和變量。 任何幫助，將不勝感激。

Answer 1

我設法弄明白了。 見下面的答案

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;
    }

並將結果打印到我的日志文件中：

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