如何将托管对象发送到本机函数以使用它？

Question

如何将托管对象发送到本机函数以使用它？

void managed_function()
{
  Object^ obj = gcnew Object();

  void* ptr = obj ??? // How to convert Managed object to void*?

  unmanaged_function(ptr);
}

// The parameter type should be void* and I can not change the type.
// This function is native but it uses managed object. Because type of ptr could not be 
// Object^ I called it "Unmanaged Function".
void unmanaged_function(void* ptr)
{
  Object^ obj = ptr ??? // How to convert void* to Managed object?

  obj->SomeManagedMethods();
}

Answer 1

在谷歌搜索,阅读MSDN并尝试一些代码后,我发现这种方法将托管对象传递给非托管函数.

这些方法显示如何将Object ^转换为void*并将void*转换为Object ^.

using namespace System;
using namespace System::Runtime::InteropServices;

void managed_function() 
{ 
  Object^ obj = gcnew Object();

  // Convert Object^ to void*
  GCHandle handle = GCHandle::Alloc(obj);
  IntPtr pointer = GCHandle::ToIntPtr(handle);
  void* ptr = pointer.ToPointer();

  unmanaged_function(ptr);

  handle.Free();
} 

void unmanaged_function(void* ptr) 
{
  // Convert void* to Object^
  IntPtr pointer(ptr);
  GCHandle handle = GCHandle::FromIntPtr(pointer);
  Object^ obj = (Object^)handle.Target;

  obj->SomeManagedMethods();
} 

注意:如果"unmanaged_function"具有可变参数,则此方法将不起作用.

Answer 2

更清洁,更好的方法是使用gcroot模板.

来自MSDN的引用如何:在本机类型中声明句柄:

gcroot模板是使用值类System :: Runtime :: InteropServices :: GCHandle的工具实现的,它为垃圾收集堆提供了"句柄".请注意,句柄本身不会被垃圾收集,并且在gcroot类中的析构函数不再使用时会释放(此析构函数不能手动调用).如果在本机堆上实例化gcroot对象,则必须在该资源上调用delete.

您的示例代码适合使用gcroot(代码使用VS 2010编译和运行):

using namespace System;
using namespace System::Runtime::InteropServices;

public ref class SomeManagedObject
{
public:
    String^ data;
    SomeManagedObject()
    {
        data = "Initial Data";
    }
    void SomeManagedMethods()
    {
        data = "Changed Data";
    }
};

void unmanaged_function(void* ptr) 
{
    gcroot<SomeManagedObject^>& obj = *((gcroot<SomeManagedObject^>*)ptr);
    obj->SomeManagedMethods();
} 

void managed_function() 
{ 
    // gcroot handles all allocations/deallocation and convertions
    gcroot<SomeManagedObject^>* pObj = new gcroot<SomeManagedObject^>();

    *pObj = gcnew SomeManagedObject();
    unmanaged_function(pObj);

    delete pObj;
}