ios - EXC_BAD_ACCESS when attempting to retrieve value using object_getIvar -

i trying learn how take advantage of objective-c runtime functions.

i have dictionary contains several name=value pairs.

e.g.

{     "recipe_description" = "delicious , 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"; } 

first, create runtime class contains ivars associated keys of each object in dictionary (e.g. ivars = recipe_description, recipe_id, recipe_image, etc). second, set values of each ivar in runtime class each corresponding object in dictionary (e.g. recipe_description = delicious , healthy, etc). finally, retrieve value of ivar.

i can retrieve values of recipe_name, recipe_id, , recipe_description, unable retrieve values of recipe_url , recipe_image. when attempt retrieve these values exc_bad_access code=2, address=0x5 error on line value = object_getivar(classinstance, ivar); in valueforivarcontainingname:class: method.

code:

- (class)wrapobjectwithname:(nsstring *)name ivarnames:(nsarray *)ivarnames {     const char *classname = [name cstringusingencoding:nsasciistringencoding];      class objectclass = objc_allocateclasspair([nsobject class], classname, 0);      (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];      (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;      (int = 0; < 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; } 

usage:

         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]); 

why can retrieve recipe_name, recipe_description, recipe_id values, not recipe_url , recipe_image values?

i'm guessing has objects being urls, maybe? i've tried converting each object in dictionary string, has no effect.

any appreciated!

i ended using valueforkey: instead, better choice.

e.g.

id value = [mycustomclassinstance valueforkey:@"key"];