[英]Initialize a reference to a C# shared pointer from C++ using SWIG
我試圖在C ++中初始化對從C#傳遞的boost共享指針的引用,同時嘗試維護繼承樹。 我希望能夠在C#中創建一個變量,然后將其傳遞給我的DLL,該DLL將在內部實例化它(以便我可以在同一上下文中管理所有內存分配)。
這是我的C ++測試用例(在SwigTest.h文件中):
#include <string>
#include <boost/shared_ptr.hpp>
template<class T>
using SRef = boost::shared_ptr<T>;
class FactoryClass
{
public:
FactoryClass() {}
~FactoryClass() {}
//Normally I would only like to use the return value, but SWIG uses polymorphism to simulate templates
//and polymorphism on the return type only is not supported by C#. (I get a Identifier 'getReference' redefined error on SwigTest.i compilation).
//So I thought I’d pass the SRef& as a parameter instead of having no parameters at all.
template <class T>
static SRef<T> getReference( SRef<T>& inout ) { inout = SRef<T>( new T(1) ); return inout; }
void testing( int& toto ) {};
};
class BaseClass
{
public:
BaseClass() { m_flag = -1; };
BaseClass(int i) { m_flag = i; };
virtual ~BaseClass() {};
virtual std::string getName() = 0;
int m_flag;
};
class FirstClass : public BaseClass
{
public:
FirstClass() {};
FirstClass(int i) : BaseClass( i ) {};
virtual ~FirstClass() {};
virtual std::string getName() { return "First Class"; };
};
class SecondClass : public BaseClass
{
public:
SecondClass() {};
SecondClass(int i) : BaseClass( i ) {};
virtual ~SecondClass() {};
virtual std::string getName() { return "Second Class"; };
};
這是我當前的SWIG接口文件:
%module SwigTest
%include "std_string.i"
%include "boost_shared_ptr.i"
%{
#include "../include/SwigTest.h"
%}
%shared_ptr( BaseClass );
%shared_ptr( FirstClass );
%shared_ptr( SecondClass );
%include "../include/SwigTest.h"
%template(BoostBasePtr) boost::shared_ptr<BaseClass>;
%template(SharedBase) SRef<BaseClass>;
%template(BoostFirstPtr) boost::shared_ptr<FirstClass>;
%template(SharedFirst)SRef<FirstClass>;
%template(getReference)FactoryClass::getReference<FirstClass>;
%template(BoostSecondPtr) boost::shared_ptr<SecondClass>;
%template(SharedSecond)SRef<SecondClass>;
%template(getReference)FactoryClass::getReference<SecondClass>;
這是在C#中行不通的方法:
public class SwigInterface
{
private FirstClass m_first;
private SecondClass m_second = new SecondClass(-2);
void TestSwig ()
{
m_first = FactoryClass.getReference( m_first ); //The returned reference is copied from C++
FactoryClass.getReference( m_second ); //m_second is never changed
FirstClass anotherFirst = new FirstClass(-1) ;
BaseClass bc = FactoryClass.getReference( anotherFirst); //bc does equal the new instance of FirstClass but anotherFirst is not correctly replaced
//This is the case I would ideally want to use
SecondClass nothing ;
FactoryClass.getReference( nothing ) ; //NullReferenceException (because the SWIG generated interface uses nothing.CPtr() to pass by pointer as it does with all refs).
}
}
我嘗試了很多%typename
體操,將FactoryClass.getReference( FirstClass )
的簽名替換為FactoryClass.getReference( out FirstClass )
(甚至引用FirstClass),但我找不到正確的方法。
在理想情況下,我只想在C#的FactoryClass中生成一個void getReference<T>( ref T inout )
,但是即使使用SWIG %extend
關鍵字添加該方法也不會生成它,因為我必須實例化每個我需要的模板。
如果我理解您的觀點,那么您已經達到了上限。 我也遇到過同樣的問題。 每個指針(無論是否智能)都在C#中失去一次多態性。
您需要使用%pragma(csharp)指令在C#端為BaseClass提供一個特殊的工廠。 然后,您需要使用csout類型映射來映射您的指針,如下所示:
%typemap(csout, excode=SWIGEXCODE)
BaseClass*, std::shared_ptr<BaseClass>, std::shared_ptr<BaseClass> & {
System.IntPtr cPtr = $imcall;
// The following line is a call to your special factory
BaseClass ret = $imclassname.createBaseClass(cPtr, $owner);$excode
return ret;
}
您的工廠可能是這樣的:
%pragma(csharp) imclasscode=%{
public static BaseClass createBaseClass(System.IntPtr cPtr, bool owner)
{
BaseClass ret = null;
if (cPtr == System.IntPtr.Zero) {
return ret;
}
string name = ($imclassname.BaseClass_getName(new System.Runtime.InteropServices.HandleRef(null, cPtr)));
switch (name)
{
case "First Class":
return new FirstClass(cPtr, owner);
case "Second Class":
return new SecondClass(cPtr, owner);
default:
return null;
}
}
%}
我沒有測試過,也許有些事情需要改變或適應。 但它應該起作用。
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