Howto implement callback interface from unmanaged DLL to .net app?

最新推荐文章于 2025-01-07 09:49:59 发布

转载最新推荐文章于 2025-01-07 09:49:59 发布 · 854 阅读

C# 专栏收录该内容

57 篇文章

订阅专栏

本文介绍如何从C++未托管DLL调用C#托管应用程序中的回调接口。通过定义兼容的委托类型并使用P/Invoke技术，可以实现C++代码与C# GUI之间的双向通信。

Howto implement callback interface from unmanaged DLL to .net app?

up vote 12 down vote favorite

in my next project I want to implement a GUI for already existing code in C++. My plan is to wrap the C++ part in a DLL and to implement the GUI in C#. My problem is that I don't know how to implement a callback from the unmanaged DLL into the manged C# code. I've already done some development in C# but the interfacing between managed and unmanaged code is new to me. Can anybody give me some hints or reading tips or a simple example to start from? Unfortunatly I could not find anything helpful.

asked Jan 30 '10 at 12:46

chrmue
916 1 10 23

add a comment

4 Answers

active oldest votes

up vote 25 down vote accepted

You don't need to use Marshal.GetFunctionPointerForDelegate(), the P/Invoke marshaller does it automatically. You'll need to declare a delegate on the C# side whose signature is compatible with the function pointer declaration on the C++ side. For example:

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

class UnManagedInterop {
  private delegate int Callback(string text);
  private Callback mInstance;   // Ensure it doesn't get garbage collected

  public UnManagedInterop() {
    mInstance = new Callback(Handler);
    SetCallback(mInstance);
  }
  public void Test() {
    TestCallback();
  }

  private int Handler(string text) {
    // Do something...
    Console.WriteLine(text);
    return 42;
  }
  [DllImport("cpptemp1.dll")]
  private static extern void SetCallback(Callback fn);
  [DllImport("cpptemp1.dll")]
  private static extern void TestCallback();
}

And the corresponding C++ code used to create the unmanaged DLL:

#include "stdafx.h"

typedef int (__stdcall * Callback)(const char* text);

Callback Handler = 0;

extern "C" __declspec(dllexport)
void __stdcall SetCallback(Callback handler) {
  Handler = handler;
}

extern "C" __declspec(dllexport)
void __stdcall TestCallback() {
  int retval = Handler("hello world");
}

That's enough to get you started with it. There are a million details that can get you into trouble, you are bound to run into some of them. The much more productive way to get this kind of code going is writing a wrapper in the C++/CLI language. That also lets you wrap a C++ class, something you can't do with P/Invoke. A decent tutorial is available here.