How do you properly create a va_list dynamically at runtime for Cocos2D CCMenu menuWithItems?

问题

I'm having a hell of a time with the CCMenu class. To create a menu with this class it forces you to call a method called initWithItems, which takes a va_list. I need to generate this list at runtime, and I read that creating a C array and passing that can function just as va_list does under the covers, only it is failing.

I have an NSArray of items I want in the va_list, and these items are a SUBCLASS of CCMenuItem, the class that menuWithItems is expecting in the va_list. If you hardcode this list at compile time, it works fine, but my attempt to create this list dynamically is not working. What is wrong with this? MenuItemButton is a CCMenuItem subclass.

NSArray *menuItems = [self getMenuItemsArray]; // Returns an NSArray of MenuItemButtons 
MenuItemButton *argList = (MenuItemButton *)malloc( sizeof(MenuItemButton *) * [menuItems count] );
[menuItems getObjects:(id *)argList];
CCMenuAdvanced* menu = [CCMenuAdvanced menuWithItems:argList];

This crashes at runtime, BAD_ACCESS. I know the va_list is supposed to be null terminated, I don't know if that is the case with my code here after calling getObjects, or if that is even the problem.

回答1:

You could simply initialize the menu using nil. For example,

CCMenu * myMenu = [CCMenuAdvanced menuWithItems:nil];

Then say you have a dynamic list of strings that you loaded at runtime, try....

// replace this with a dynamically loaded array of items...
NSArray* dynamicArray = [NSArray arrayWithObjects:@"red", @"blue", @"green", nil];


for (NSString* item in dynamicArray)
{
    CCMenuItem *menuItem = [CCMenuItemFont itemFromString: item target: self     selector:@selector(menuCallback:)];
    [myMenu addChild:menuItem];
}

回答2:

va_list isn't always an array. With 32-bit gcc, it is, with 64-bit it isn't. Don't rely on it.

va_list is generated by a function that gets a variable number of arguments:

#include <stdarg.h>
void f(int x, ...) {
    va_list va;
    va_start(va, x);
    function_that_wants_va(va);
    va_end(va);
}
void g(void) {
    f(1,2,3,4);
}

来源：https://stackoverflow.com/questions/9283382/how-do-you-properly-create-a-va-list-dynamically-at-runtime-for-cocos2d-ccmenu-m

标签

iphone

cocos2d-iphone

variadic-functions