从C++成员函数调用Objective-C方法？

Question

我有一个class(EAGLView)调用类的成员函数C++没有问题.现在,问题是我需要在C++该类中调用一个objective-C function [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer];我在C++语法中无法做到的.

我可以将这个Objective-C调用包装到同一个Objective-C类中,它首先调用C++类,但后来我需要以某种方式调用该方法C++,而我无法弄清楚如何去做.

我试图给一个指向EAGLViewC++成员函数的对象的指针,并EAGLView.h在我的C++类头中包含" " 但我得到了3999个错误..

那么......我该怎么做？一个例子很好..我只发现C了这样做的纯粹例子.

Answer 1

如果仔细操作,可以将C++与Objective-C混合使用.有一些警告,但一般来说,他们可以混合.如果你想将它们分开,你可以设置一个标准的C包装函数,它为Objective-C对象提供了一个非Objective-C代码的可用C风格接口(为你的文件选择更好的名字,我选择了这些名字)为了冗长):

为MyObject-C-Interface.h

#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);
}

包装器函数不需要.m与Objective-C类在同一个文件中,但它所存在的文件需要编译为Objective-C代码.声明包装函数的标头需要包含在CPP和Objective-C代码中.

(注意:如果Objective-C实现文件的扩展名为".m",它将不会在Xcode下链接.".mm"扩展名告诉Xcode期望Objective-C和C++的组合,即Objective-C++. )

您可以使用PIMPL惯用法以Object-Orientented方式实现上述内容.实施只是略有不同.简而言之,您将包装函数(在"MyObject-C-Interface.h"中声明)放在一个类中,该类具有指向MyClass实例的(私有)void指针.

MyObject-C-Interface.h (PIMPL)

#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,包装器方法不再需要指向MyClass实例的void指针; 它现在是MyClassImpl的私有成员.init方法用于实例化MyClass实例;

MyObject.h (PIMPL)

#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,MyClass是通过调用MyClassImpl :: init来实例化的.你可以在MyClassImpl的构造函数中实例化MyClass,但这通常不是一个好主意.MyClass实例从MyClassImpl的析构函数中被破坏.与C风格的实现一样,包装器方法只是遵循MyClass的相应方法.

MyCPPClass.h (PIMPL)

#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的私有实现来访问MyClass的调用.如果您正在开发便携式应用程序,这种方法可能是有利的; 你可以简单地将MyClass的实现替换为另一个特定于另一个平台......但老实说,这是否是一个更好的实现更多的是品味和需求的问题.

Answer 2

您可以将代码编译为Objective-C++ - 最简单的方法是将.cpp重命名为.mm.如果你包含它会正确编译EAGLView.h(你因为C++编译器不理解任何Objective-C特定的关键字而得到很多错误),你可以(大部分)混合使用Objective-C和C++但是你喜欢.

Answer 3

最简单的解决方案是简单地告诉Xcode将所有内容编译为Objective C++.

为Compile Sources设置项目或目标设置与Objective C++相同并重新编译.

然后你可以在任何地方使用C++或Objective C,例如:

void CPPObject::Function( ObjectiveCObject* context, NSView* view )
{
   [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)view.layer]
}

这与将.cpp或.m重命名为.mm的所有源文件具有相同的效果.

这有两个小缺点:clang无法分析C++源代码; 一些相对奇怪的C代码不能在C++下编译.

Answer 4

步骤1

创建一个目标c文件(.m文件)及其相应的头文件.

//头文件(我们称之为"ObjCFunc.h")

#ifndef test2_ObjCFunc_h
#define test2_ObjCFunc_h
@interface myClass :NSObject
-(void)hello:(int)num1;
@end
#endif

//对应的Objective C文件(我们称之为"ObjCFunc.m")

#import <Foundation/Foundation.h>
#include "ObjCFunc.h"
@implementation myClass
//Your objective c code here....
-(void)hello:(int)num1
{
NSLog(@"Hello!!!!!!");
}
@end

第2步

现在我们将实现一个c ++函数来调用我们刚创建的目标c函数!因此,我们将定义一个.mm文件及其相应的头文件(此处将使用".mm"文件,因为我们将能够在文件中使用Objective C和C++编码)

//头文件(我们称之为"ObjCCall.h")

#ifndef __test2__ObjCCall__
#define __test2__ObjCCall__
#include <stdio.h>
class ObjCCall
{
public:
static void objectiveC_Call(); //We define a static method to call the function directly using the class_name
};
#endif /* defined(__test2__ObjCCall__) */

//对应的Objective C++文件(我们称之为"ObjCCall.mm")

#include "ObjCCall.h"
#include "ObjCFunc.h"
void ObjCCall::objectiveC_Call()
{
//Objective C code calling.....
myClass *obj=[[myClass alloc]init]; //Allocating the new object for the objective C   class we created
[obj hello:(100)];   //Calling the function we defined
}

第3步

调用c ++函数(实际调用目标c方法)

#ifndef __HELLOWORLD_SCENE_H__
#define __HELLOWORLD_SCENE_H__
#include "cocos2d.h"
#include "ObjCCall.h"
class HelloWorld : public cocos2d::Layer
{
public:
// there's no 'id' in cpp, so we recommend returning the class instance pointer
static cocos2d::Scene* createScene();
// Here's a difference. Method 'init' in cocos2d-x returns bool, instead of returning  'id' in cocos2d-iphone
virtual bool init();
// a selector callback
void menuCloseCallback(cocos2d::Ref* pSender);
void ObCCall();  //definition
// implement the "static create()" method manually
CREATE_FUNC(HelloWorld);
};
#endif // __HELLOWORLD_SCENE_H__

//最后呼叫

#include "HelloWorldScene.h"
#include "ObjCCall.h"
USING_NS_CC;
Scene* HelloWorld::createScene()
{
// 'scene' is an autorelease object
auto scene = Scene::create();
// 'layer' is an autorelease object
auto layer = HelloWorld::create();
// add layer as a child to scene
scene->addChild(layer);
// return the scene
return scene;
}
// on "init" you need to initialize your instance
bool HelloWorld::init()
{
//////////////////////////////
// 1. super init first
if ( !Layer::init() )
{
    return false;
}
Size visibleSize = Director::getInstance()->getVisibleSize();
Vec2 origin = Director::getInstance()->getVisibleOrigin();

/////////////////////////////
// 2. add a menu item with "X" image, which is clicked to quit the program
//    you may modify it.

// add a "close" icon to exit the progress. it's an autorelease object
auto closeItem = MenuItemImage::create(
                                       "CloseNormal.png",
                                       "CloseSelected.png",
                                       CC_CALLBACK_1(HelloWorld::menuCloseCallback,  this));

closeItem->setPosition(Vec2(origin.x + visibleSize.width - closeItem->getContentSize().width/2 ,
                            origin.y + closeItem->getContentSize().height/2));

// create menu, it's an autorelease object
auto menu = Menu::create(closeItem, NULL);
menu->setPosition(Vec2::ZERO);
this->addChild(menu, 1);

/////////////////////////////
// 3. add your codes below...

// add a label shows "Hello World"
// create and initialize a label

auto label = Label::createWithTTF("Hello World", "fonts/Marker Felt.ttf", 24);

// position the label on the center of the screen
label->setPosition(Vec2(origin.x + visibleSize.width/2,
                        origin.y + visibleSize.height - label- >getContentSize().height));
// add the label as a child to this layer
this->addChild(label, 1);
// add "HelloWorld" splash screen"
auto sprite = Sprite::create("HelloWorld.png");
// position the sprite on the center of the screen
sprite->setPosition(Vec2(visibleSize.width/2 + origin.x, visibleSize.height/2 +     origin.y));
// add the sprite as a child to this layer
this->addChild(sprite, 0);
this->ObCCall();   //first call
return true;
}
void HelloWorld::ObCCall()  //Definition
{
ObjCCall::objectiveC_Call();  //Final Call  
}
void HelloWorld::menuCloseCallback(Ref* pSender)
{
#if (CC_TARGET_PLATFORM == CC_PLATFORM_WP8) || (CC_TARGET_PLATFORM ==   CC_PLATFORM_WINRT)
MessageBox("You pressed the close button. Windows Store Apps do not implement a close    button.","Alert");
return;
#endif
Director::getInstance()->end();
#if (CC_TARGET_PLATFORM == CC_PLATFORM_IOS)
exit(0);
#endif
}

希望这个有效!

Answer 5

您需要将C++文件视为Objective-C++.您可以通过将foo.cpp重命名为foo.mm(.mm是obj-c ++扩展名)在xcode中执行此操作.然后正如其他人所说的标准obj-c消息语法将起作用.