把C++/CLI委托传入本地代码

参考: http://resnikb.wordpress.com/2009/05/18/passing-ccli-delegate-to-native-code/

 

C++/CLI可以直接执行C++, 这个没有问题, 那么反过来呢?

比如底层C++进行一项任务, 完成了需要通知上层的C++/CLI, 总不能在上面不停地查询吧?

通常这是通过回调来实现的, 说漂亮点就是观察者模式, 说成.net的就是委托.

而委托, 本质是就是函数指针. 以前也提到过C++委托的实现.

.net提供了一个方法把委托转换成函数指针: Marshal::GetFunctionPointerForDelegate

 跟String的转换一样, 需要注意保证内存指针不会被托管机制移动/回收.

// DelegateCallback.cpp : main project file.#include "stdafx.h"#include <assert.h>#pragma unmanagedtypedef void (__stdcall* EventCallback)(int);class Native{public:/// 注册回调函数static void RegisterCallback(EventCallback callback){assert(0 != callback);ms_callback = callback;}/// 调用注册的回调函数static void Invoke(int i){assert(0 != ms_callback);ms_callback(i);};private:static EventCallback ms_callback;};EventCallback Native::ms_callback = 0;#pragma managedusing namespace System;using namespace System::Runtime::InteropServices;public delegate void EventDelegate(int i);ref class NativeInterface{public:NativeInterface(){// 从成员函数创建一个委托this->nativeCallback = gcnew EventDelegate(this, &NativeInterface::Callback);// 保证委托不会被内存移动和垃圾回收掉this->delegateHandle = GCHandle::Alloc(this->nativeCallback);// 转换为函数指针注册IntPtr ptr = Marshal::GetFunctionPointerForDelegate(this->nativeCallback);Native::RegisterCallback( static_cast<EventCallback>(ptr.ToPointer()) );}~NativeInterface(){// 释放委托句柄if (this->delegateHandle.IsAllocated)this->delegateHandle.Free();}private:void Callback(int i){Console::WriteLine("托管命令行输出: {0}", i);}private:GCHandle delegateHandle;EventDelegate^ nativeCallback;};//------------------------------------------------------------------------------int main(array<System::String^>^ args){NativeInterface^ ni = gcnew NativeInterface();// 这个可以在native c++中调用Native::Invoke(12345);delete ni;ni = nullptr; return 0;}