假设我有一个用于计算 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# 调用这个函数,并且我想使用 C++/CLI 作为“桥梁”。然而这个 C++ 函数有点慢。因此,调用此函数的 C# 代码需要获取回调,以 % 形式告诉它该函数已经进行了多远。
C# 代码可能需要一些状态,例如进度条,处理此信息。
因此,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;
};
};
and
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() 可以正常工作:-)。它按预期将调用转发给 Cpp::PI::compute()。
但是,当 Cpp::PI::compute() 运行时,如何让 C++ 库将进度更新转发到 CSharp.PI.progress() 呢?
预先感谢您的任何答复!
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,覆盖摘要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."
);
}
}
}
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