Question

说我有一个用于计算PI的C ++库函数：

// pi.h:
#ifdef BUILDING_DLL
#define DLL_MACRO __declspec(dllexport)
#else
#define DLL_MACRO __declspec(dllimport)
#endif

namespace Cpp {
  class PI {
  public:
    static double DLL_MACRO compute();
  };
}; 

// pi.cpp: 
#include "pi.h"
#include <cmath>

double 
Cpp::PI::compute() {
   // Leibnitz summation formulae:
   double sum = 0.0;
   for(long n = 0; n < 100*1000*1000; n++)
     sum += 4.0*pow(-1.0, n)/(2*n + 1.0);
   return sum;
}

我需要从C＃调用此函数，并且我想使用C ++ / CLI作为“桥”。但是这个C ++函数有点慢。因此，调用此函数的C＃代码需要获取回调函数，告诉它函数的进度是多少％。 C＃代码可能需要一些状态，例如进度条，处理此信息。所以来自C ++的回调必须进入C＃端的成员函数。

所以我介绍一下：

// piCLI.h: The C++/CLI "bridge" between C# and C++
#include "pi.h"
#pragma once
namespace CLI {
   public ref class PI abstract {
   public:
      double compute() {
        return Cpp::PI::compute();
      }
      virtual void progress(int percentCompleted) = 0;        
   };
 };

和

 namespace CSharp
 {
    public class PI : CLI.PI
    {
       public override void progress(int percentCompleted)
       {
          System.Console.WriteLine(percentCompleted + "% completed.");
       }
     }
  }

现在调用CSharp.PI.compute（）工作正常:-)。它按预期将调用转发给Cpp :: PI :: compute（）。

但是如何在Cpp :: PI :: compute（）运行的同时让C ++库将进度更新转发到CSharp.PI.progress（）？

提前感谢您的任何答案！

Answer 1

我也会采用函数指针/委托方法：

// pi.h:
#pragma once

#ifndef DLL_MACRO
#ifdef BUILDING_DLL
#define DLL_MACRO __declspec(dllexport)
#else
#define DLL_MACRO __declspec(dllimport)
#endif
#endif

namespace Cpp {
    typedef void (__stdcall *ComputeProgressCallback)(int);

    class PI {
    public:
        static double DLL_MACRO compute(ComputeProgressCallback callback);
    };
}

// pi.cpp: 
#include "pi.h"
#include <cmath>

double Cpp::PI::compute(Cpp::ComputeProgressCallback callback) {
    double sum = 0.;
    for (long n = 0L; n != 100000000L; ++n) {
        sum += 4. * std::pow(-1., n) / (2L * n + 1.);
        callback(/*impl*/);
    }
    return sum;
}

// piCLI.h: The C++/CLI "bridge" between C# and C++
#pragma once
#include "pi.h"

namespace CLI {
    public delegate void ComputeProgressDelegate(int percentCompleted);

    public ref class PI abstract sealed {
    public:
        static double compute(ComputeProgressDelegate^ callback) {
            using System::IntPtr;
            using System::Runtime::InteropServices::Marshal;

            IntPtr cbPtr = Marshal::GetFunctionPointerForDelegate(callback);
            return Cpp::PI::compute(
                static_cast<Cpp::ComputeProgressCallback>(cbPtr.ToPointer())
            );
        }
    };
}

namespace CSharp {
    public static class PI {
        public static double compute() {
            CLI.PI.compute(
                percentCompleted => System.Console.WriteLine(
                    percentCompleted.ToString() + "% completed."
                )
            );
        }
    }
}

或者，覆盖抽象progress方法而不是在C＃端创建委托：

// piCLI.h: The C++/CLI "bridge" between C# and C++
#pragma once
#include "pi.h"

namespace CLI {
    public ref class PI abstract {
        delegate void ComputeProgressDelegate(int percentCompleted);

    public:
        double compute() {
            using System::IntPtr;
            using System::Runtime::InteropServices::Marshal;

            ComputeProgressDelegate^ callback = gcnew ComputeProgressDelegate(
                this,
                &PI::progress
            );
            IntPtr cbPtr = Marshal::GetFunctionPointerForDelegate(callback);
            return Cpp::PI::compute(
                static_cast<Cpp::ComputeProgressCallback>(cbPtr.ToPointer())
            );
        }

    protected:
        virtual void progress(int percentCompleted) abstract;
    };
}

namespace CSharp {
    public sealed class PI : CLI.PI {
        protected override void progress(int percentCompleted) {
            System.Console.WriteLine(
                percentCompleted.ToString() + "% completed."
            );
        }
    }
}

Answer 2

将C ++ / cli定义的Native函数作为回调传递给本机C ++，并在回调时使用gcroot调用托管C＃函数。

从C ++回调到C＃的回调

2 个答案: