Ios EXC_尝试使用object_getIvar检索值时访问错误

我试图学习如何利用objective-c运行时函数

我有一本字典，里面有几个

name=value

对

例如

{
    "recipe_description" = "Delicious and healthy.";
    "recipe_id" = 7042366;
    "recipe_image" = "http://www.fatsecret.com/static/recipe/b5b8ccb7-badd-4a7f-8dd4-0ffe4aba8c6d.jpg";
    "recipe_name" = "Brown Rice & Cherry Tomato Cooked Salad";
    "recipe_url" = "http://www.fatsecret.com/recipes/brown-rice-and-cherry-tomato-cooked-salad/Default.aspx";
}

id value = [MyCustomClassInstance valueForKey:@"key"];

首先，我创建一个运行时类，其中包含与字典中每个对象的键相关联的IVAR（例如ivars=recipe\u description、recipe\u id、recipe\u image等）。其次，我将运行时类中每个Ivar的值设置为字典中每个对应的对象（例如，recipe_description=Delicious and Health等）。最后，我检索Ivar的值

我可以检索配方名称、配方id和配方描述的值，但无法检索配方url和配方图像的值。当我试图检索这些值时，我在

value=object\u getIvar（classInstance，ivar）行上得到一个
EXC\u BAD\u ACCESS code=2，address=0x5
错误valueForIvarContainingName:class:

方法中的code>

代码：

- (Class)wrapObjectWithName:(NSString *)name ivarNames:(NSArray *)ivarNames
{
    const char *className = [name cStringUsingEncoding:NSASCIIStringEncoding];

    Class objectClass = objc_allocateClassPair([NSObject class], className, 0);

    for (NSString *key in ivarNames)
    {
        const char *iVarName = [key cStringUsingEncoding:NSASCIIStringEncoding];

        class_addIvar(objectClass, iVarName, sizeof(NSString*), log2(sizeof(NSString*)), @encode(NSString*));
    }

    objc_registerClassPair(objectClass);

    return objectClass;
}

- (void)mapValues:(NSDictionary *)dictionary toVariablesInClass:(id)classInstance
{
    NSArray *dictionaryObjectKeys = [dictionary allKeys];

    for (NSString *key in dictionaryObjectKeys)
    {
        const char *iVarName = [key cStringUsingEncoding:NSASCIIStringEncoding];
        Ivar ivar = class_getInstanceVariable([classInstance class], iVarName);

        id value = dictionary[key];

        object_setIvar(classInstance, ivar, value);
    }
}

- (id)valueForIvarContainingName:(NSString *)anIvarName class:(id)classInstance
{
    unsigned int outCount;
    Ivar *iVarList = class_copyIvarList([classInstance class], &outCount);

    id value;

    for (int i = 0; i < outCount; i++)
    {
        Ivar ivar = iVarList[i];

        NSString *ivarName = [NSString stringWithCString:ivar_getName(ivar) encoding:NSASCIIStringEncoding];

        if ([ivarName rangeOfString:anIvarName].location != NSNotFound)
        {
            value = object_getIvar(classInstance, ivar);
            break;
        }
    }

    free(iVarList);

    return value;
}

         NSArray *ivarNames = [dictionary allKeys];
         Class FSRecipe = [self wrapObjectWithName:@"FSRecipe" ivarNames:ivarNames];

         id recipe = [[FSRecipe alloc] init];
         [self mapValues:dictionary toVariablesInClass:recipe];

         NSLog(@"%@", [self valueForIvarContainingName:@"image" class:recipe]);

为什么我可以检索配方名称、配方描述、配方id值，而不能检索配方url和配方图像值

我猜这可能和作为URL的对象有关吧？我尝试将字典中的每个对象转换为字符串，但没有效果

---

非常感谢您的帮助

我最终使用了

valueForKey:

，这可能是一个更好的选择

例如

{
    "recipe_description" = "Delicious and healthy.";
    "recipe_id" = 7042366;
    "recipe_image" = "http://www.fatsecret.com/static/recipe/b5b8ccb7-badd-4a7f-8dd4-0ffe4aba8c6d.jpg";
    "recipe_name" = "Brown Rice & Cherry Tomato Cooked Salad";
    "recipe_url" = "http://www.fatsecret.com/recipes/brown-rice-and-cherry-tomato-cooked-salad/Default.aspx";
}

id value = [MyCustomClassInstance valueForKey:@"key"];

---

哎呀。我本想把它拿出来的，接得好。我正在将对象转换为字符串表示，看看这是否能修复EXC_BAD_访问；不管怎么说，这都不是问题的原因。我刚刚发现，出于某种原因，object_getIvar中的ivar为零，但ivar肯定存在，并且有一个值；您的代码在

[self-valueForIvarContainingName:@“image”类：recipe]

和

[self-valueForIvarContainingName:@“url”类：recipe]

中都能正常工作，这些IVAR的值是

NSURL

实例。@JoshCaswell，应用程序唯一的另一部分是将这些对象存储在数组中，然后在collectionViewCell上显示值。我猜你为什么没有重现同样的错误。