objective c - Editing an NSMutableDictionary sub-dictionary -

i have nsmutabledictionary made json file.

nsmutabledictionary *result=//from json string 

than , need edit result ,which built :

{     slots =     (                 {             capacity = 1;             slot = sybiwqgdww;             taken =             (                 "11:45-12:45",                 "12:45-17:45"             );         },                 {             capacity = 1;             slot = wnysjezamu;             taken =             (                 "12:00-13:00",                 "13:00-18:00"             );         }     ); } 

to array of fields have :

   nsmutablearray *slots=[result objectforkey:@"slots"]; 

than dictionaries :

 for(nsmutabledictionary *dic in slots)             [dic setobject:@"1" forkey:@"slot"];//crash because edit in loop 

now crash when trying change field in loop.

how can change field ?

edit

this how make dictionary json (which mutable copy result! )

-(nsdictionary*)getdictionaryforjsonwithstring:(nsstring*)string {     nsstring *datastring=string;     nsdata *mydata=[datastring datausingencoding:nsasciistringencoding];     nserror *error;     nsdictionary *datadic = [nsjsonserialization jsonobjectwithdata:mydata options:kniloptions error:&error];     //nslog(@"getdictionaryforjsonwithstring: data is: %@",datadic);     return datadic;  }      nsmutabledictionary *result=[[self getdictionaryforjsonwithstring:json] mutablecopy]; 

when create dictionary json, need set option create mutable instances, , should both containers , leaves:

option: nsjsonreadingmutablecontainers | nsjsonreadingmutableleaves