Using CREATE_FUNC in Cocos2dx

Question

Can anyone explain me why do we need to use CREATE_FUNC in Cocos2dx? I saw it in the HelloWorld samples and don't understand it clearly. Please, tell me more detail. Thanks.

Crites

Answer 1

We don't need to use it, it is a helper macro which expands to this :

/**
 * define a create function for a specific type, such as CCLayer
 * @__TYPE__ class type to add create(), such as CCLayer
 */
#define CREATE_FUNC(__TYPE__)
static __TYPE__* create()
{
    __TYPE__ *pRet = new(std::nothrow) __TYPE__();
    if (pRet && pRet->init())
    {
        pRet->autorelease();
        return pRet;
    }
    else
    {
        delete pRet;
        pRet = NULL;
        return NULL;
    }
}

It basically "writes" the create() method for your type, and calls your init() implementation. Its main purpose is to call the autorelease() method, so that you wan't forget about it, if you were to write your own create(). It may not seem as much, but it takes a little of you.

Tip : in most IDEs you can Control + Click (Command on MAC) on pieces of code like functions and macros, and the IDE will take you to it.

Let me know if something is still not clear.

EDIT : Question from comment : For specific, if I want to write a CCCarSprite which extends from CCSprite and have some more functions like run, crash...Do I need to call CREATE_FUNCTION(CCCarSprite)?

No, you don't. What you HAVE to do is call one of superclasses init… methods. This would be best done from your constructor or from your init() in the subclass.

EDIT 2: Second question from comment : Just one more, in the HelloWorld sample in Cocos2dx, why do they need to call CREATE_FUNCTION manually? The don't need to, but it may be considered "good practice" when working with cocos to use their macros, because when they cange something in the create() function implemented by the macro in new version they only need to update it in one place - the macro definition. This leaves less room for error, as there is virtually no chance to "forget" about a place to change the code to new version.

Ldopa

For specific, if I want to write a CCCarSprite which extends from CCSprite and have some more functions like run, crash...Do I need to call CREATE_FUNCTION(CCCarSprite)? – Crites

Just one more, in the HelloWorld sample in Cocos2dx, why do they need to call CREATE_FUNCTION manually? – Crites

Answer 2

The more compelling reason to define CREATE_FUNC macro in your function(apart from the memory management) is that, without declaring this, your init() method will never be called.( Check out this piece of code in the macro expansion => if (pRet && pRet->init()))

So this is actually much more than memory management. You can try to put logs in your init method and actually check to verify this.

Bullring

Good answer. I'm new to Cocos2d-x (after some years of Cocos2D-Iphone) and have a hard time understanding all these things about the node structure/lifetime - it's never described in any documentation. At least I never found any. How are we supposed to initialise children of nodes/sprites, sending some parameters? – Deaf

Answer 3

CREAT_FUNC(ClassName) just a macro that help us shorty out code. It contains default ClassName *create() and bool init() functions. After done that, you should implement bool ClassName::init() on your ClassName.cpp file. You could show the details of definition, then you'll find out. Hope that'll help.

Ligniform