从C ++成员函数调用Objective-C方法? [英] Calling Objective-C method from C++ member function?
问题描述
我有一个类(EAGLView)，它可以毫无问题地调用C++类的成员函数.现在，问题是我需要在该C++类中调用一个objective-C function [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer];，而在C++语法中是无法实现的.
I have a class (EAGLView) which calls a member function of a C++ class without problems. Now, the problem is that I need to call in that C++ class a objective-C function [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer]; which I cannot do in C++ syntax.
我可以将此Objective-C调用包装到相同的Objective-C类中，该类首先称为C ++类，但随后我需要以某种方式从C++调用该方法，并且我不知道该怎么做它.
I could wrap this Objective-C call to the same Objective-C class which in the first place called the C++ class, but then I need to somehow call that method from C++, and I cannot figure out how to do it.
我试图将指向EAGLView对象的指针提供给C ++成员函数，并在我的C++类标题中包含"EAGLView.h"，但出现3999错误.
I tried to give a pointer to EAGLView object to the C++ member function and include the "EAGLView.h" in my C++ class header but I got 3999 errors..
所以..我应该怎么做?一个例子会很好..我只找到纯的C例子.
So.. how should I do this? An example would be nice.. I only found pure C examples of doing this.
推荐答案
如果认真执行，可以将C ++与Objective-C混合使用.有一些警告，但总的来说，它们可以混合在一起.如果要将它们分开，则可以设置一个标准的C包装函数，该函数从非Object-C代码中为Objective-C对象提供一个可用的C风格的接口(为您的文件选择更好的名称，我选择了这些名称表示冗长):
You can mix C++ with Objective-C if you do it carefully. There are a few caveats but generally speaking they can be mixed. If you want to keep them separate, you can set up a standard C wrapper function that gives the Objective-C object a usable C-style interface from non-Objective-C code (pick better names for your files, I have picked these names for verbosity):
#ifndef __MYOBJECT_C_INTERFACE_H__
#define __MYOBJECT_C_INTERFACE_H__
// This is the C "trampoline" function that will be used
// to invoke a specific Objective-C method FROM C++
int MyObjectDoSomethingWith (void *myObjectInstance, void *parameter);
#endif
MyObject.h
#import "MyObject-C-Interface.h"
// An Objective-C class that needs to be accessed from C++
@interface MyObject : NSObject
{
int someVar;
}
// The Objective-C member function you want to call from C++
- (int) doSomethingWith:(void *) aParameter;
@end
MyObject.mm
#import "MyObject.h"
@implementation MyObject
// C "trampoline" function to invoke Objective-C method
int MyObjectDoSomethingWith (void *self, void *aParameter)
{
// Call the Objective-C method using Objective-C syntax
return [(id) self doSomethingWith:aParameter];
}
- (int) doSomethingWith:(void *) aParameter
{
// The Objective-C function you wanted to call from C++.
// do work here..
return 21 ; // half of 42
}
@end
MyCPPClass.cpp
#include "MyCPPClass.h"
#include "MyObject-C-Interface.h"
int MyCPPClass::someMethod (void *objectiveCObject, void *aParameter)
{
// To invoke an Objective-C method from C++, use
// the C trampoline function
return MyObjectDoSomethingWith (objectiveCObject, aParameter);
}
包装器功能 不需要 与Objective-C类位于同一.m文件中，但是它确实存在于 需要被编译为Objective-C代码 .声明包装函数的标头必须同时包含在CPP和Objective-C代码中.
The wrapper function does not need to be in the same .m file as the Objective-C class, but the file that it does exist in needs to be compiled as Objective-C code. The header that declares the wrapper function needs to be included in both CPP and Objective-C code.
(注意:如果给Objective-C实现文件提供扩展名".m"，则它将不会在Xcode下链接.扩展名".mm"告诉Xcode期望使用Objective-C和C ++的组合，即Objective -C ++.)
(NOTE: if the Objective-C implementation file is given the extension ".m" it will not link under Xcode. The ".mm" extension tells Xcode to expect a combination of Objective-C and C++, i.e., Objective-C++.)
您可以使用 PIMPL惯用语以面向对象的方式实现上述功能.实现只是略有不同.简而言之，将包装函数(在"MyObject-C-Interface.h"中声明)放置在一个类中，该类具有指向MyClass实例的(私有)无效指针.
You can implement the above in an Object-Orientented manner by using the PIMPL idiom. The implementation is only slightly different. In short, you place the wrapper functions (declared in "MyObject-C-Interface.h") inside a class with a (private) void pointer to an instance of MyClass.
#ifndef __MYOBJECT_C_INTERFACE_H__
#define __MYOBJECT_C_INTERFACE_H__
class MyClassImpl
{
public:
MyClassImpl ( void );
~MyClassImpl( void );
void init( void );
int doSomethingWith( void * aParameter );
void logMyMessage( char * aCStr );
private:
void * self;
};
#endif
请注意，包装方法不再需要指向MyClass实例的void指针；它现在是MyClassImpl的私人成员. init方法用于实例化MyClass实例；
Notice the wrapper methods no longer require the void pointer to an instance of MyClass; it is now a private member of MyClassImpl. The init method is used to instantiate a MyClass instance;
#import "MyObject-C-Interface.h"
@interface MyObject : NSObject
{
int someVar;
}
- (int) doSomethingWith:(void *) aParameter;
- (void) logMyMessage:(char *) aCStr;
@end
MyObject.mm (PIMPL)
#import "MyObject.h"
@implementation MyObject
MyClassImpl::MyClassImpl( void )
: self( NULL )
{ }
MyClassImpl::~MyClassImpl( void )
{
[(id)self dealloc];
}
void MyClassImpl::init( void )
{
self = [[MyObject alloc] init];
}
int MyClassImpl::doSomethingWith( void *aParameter )
{
return [(id)self doSomethingWith:aParameter];
}
void MyClassImpl::logMyMessage( char *aCStr )
{
[(id)self doLogMessage:aCStr];
}
- (int) doSomethingWith:(void *) aParameter
{
int result;
// ... some code to calculate the result
return result;
}
- (void) logMyMessage:(char *) aCStr
{
NSLog( aCStr );
}
@end
请注意，通过调用MyClassImpl :: init实例化了MyClass.您可以在MyClassImpl的构造函数中实例化MyClass，但这通常不是一个好主意. MyClass实例是从MyClassImpl的析构函数中析构的.与C样式的实现一样，包装器方法仅遵循MyClass的相应方法.
Notice that MyClass is instantiated with a call to MyClassImpl::init. You could instantiate MyClass in MyClassImpl's constructor, but that generally isn't a good idea. The MyClass instance is destructed from MyClassImpl's destructor. As with the C-style implementation, the wrapper methods simply defer to the respective methods of MyClass.
#ifndef __MYCPP_CLASS_H__
#define __MYCPP_CLASS_H__
class MyClassImpl;
class MyCPPClass
{
enum { cANSWER_TO_LIFE_THE_UNIVERSE_AND_EVERYTHING = 42 };
public:
MyCPPClass ( void );
~MyCPPClass( void );
void init( void );
void doSomethingWithMyClass( void );
private:
MyClassImpl * _impl;
int _myValue;
};
#endif
MyCPPClass.cpp (PIMPL)
#include "MyCPPClass.h"
#include "MyObject-C-Interface.h"
MyCPPClass::MyCPPClass( void )
: _impl ( NULL )
{ }
void MyCPPClass::init( void )
{
_impl = new MyClassImpl();
}
MyCPPClass::~MyCPPClass( void )
{
if ( _impl ) { delete _impl; _impl = NULL; }
}
void MyCPPClass::doSomethingWithMyClass( void )
{
int result = _impl->doSomethingWith( _myValue );
if ( result == cANSWER_TO_LIFE_THE_UNIVERSE_AND_EVERYTHING )
{
_impl->logMyMessage( "Hello, Arthur!" );
}
else
{
_impl->logMyMessage( "Don't worry." );
}
}
您现在可以通过MyClassImpl的私有实现访问对MyClass的调用.如果您正在开发便携式应用程序，则此方法可能会很有优势.您可以简单地将MyClass的实现与其他平台的实现交换掉……但是说实话，这是否是更好的实现，更多地取决于品味和需求.
You now access calls to MyClass through a private implementation of MyClassImpl. This approach can be advantageous if you were developing a portable application; you could simply swap out the implementation of MyClass with one specific to the other platform ... but honestly, whether this is a better implementation is more a matter of taste and needs.
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