NSJSONSerialization results in EXC_BAD_ACCESS

Question

Currently I am writing an app (Target iOS 6, ARC enabled) that uses JSON for data transmission and Core Data for persistent storage. The JSON data is generated out of a MySQL database by a PHP script via json_encode.

My Problem is that with data from certain tables the following code fails:

- (NSDictionary *)executeFetch:(NSString *)query
{
    NSURL *requesturl = [NSURL URLWithString:[query stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];

    NSError *dataError = nil;
    self.jsonData = [NSData dataWithContentsOfURL:requesturl options:kNilOptions error:&dataError];

    NSError *error = nil;
    self.jsonSerializationResult = [NSJSONSerialization JSONObjectWithData:self.jsonData options:NSJSONReadingMutableContainers|NSJSONReadingMutableLeaves error:&error];

    return self.jsonSerializationResult;

}

The program always crashes with an EXC_BAD_ACCESS error on the line where it says self.jsonSerializationResult and Instruments says that there was a Zombie detected. I know that this means that some object I send a message to is nil, but I can't find out how to fix it... That's what Instruments has to say:

#   Address Category    Event Type  RefCt   Timestamp   Size    Responsible Library Responsible Caller
0   0xa1b8a70   CFString (mutable)  Malloc  1   00:01.603.081   32  Foundation  -[NSPlaceholderMutableString initWithBytesNoCopy:length:encoding:freeWhenDone:]
1   0xa1b8a70   CFString (mutable)  Release 0   00:01.603.137   0   Foundation  newJSONValue
2   0xa1b8a70   CFString (mutable)  Zombie  -1  00:01.603.259   0   Foundation  newJSONString

My program works with every JSON output except for this one:

{
   "termin":[
      {
         "termin_id":"17",
         "veranstaltung_id":"20",
         "beginn":"2012-09-28 17:00:00",
         "ende":"2012-09-28 18:00:00",
         "freie_pl\u00e4tze":null
      },
      {
         "termin_id":"18",
         "veranstaltung_id":"26",
         "beginn":"2012-09-28 19:00:00",
         "ende":"2012-09-28 20:00:00",
         "freie_pl\u00e4tze":null
      },
      {
         "termin_id":"19",
         "veranstaltung_id":"26",
         "beginn":"2012-09-28 21:00:00",
         "ende":"2012-09-28 22:00:00",
         "freie_pl\u00e4tze":null
      },
      {
         "termin_id":"20",
         "veranstaltung_id":"46",
         "beginn":"2012-09-28 19:00:00",
         "ende":"2012-09-28 20:00:00",
         "freie_pl\u00e4tze":null
      },
      {
         "termin_id":"24",
         "veranstaltung_id":"66",
         "beginn":"2012-09-28 22:00:00",
         "ende":"2012-09-28 22:30:00",
         "freie_pl\u00e4tze":"120"
      }
   ]
}

I thought about some possible error sourced but none seems to be the responsible:

• jsonData or jsonSerializationResult could be nil: they aren't
• PHP generated invalid JSON: checked for that with a validator
• null Values: not a problem with other tables

Has anybody got an idea?

Answer 1

It looks like a bug/shortcoming with NSJSONSerialization. The problem is caused by the escaped unicode characters (freie_pl\u00e4tze instead of freie_plätze). You have two options -

1. Convert the escaped Unicode to real Unicode characters. Try this SO answer
2. Use another JSON engine, such as JSONKit. JSONKit also claims to be more performant than NSJSONSerialization.

Answer 2

I know this question has been answered but I think some beginners may have the same issue as me and be brought to this question.

The EXC_BAD_ACCESS message was caused by malformed JSON. As I had accidentally used the same name for an Object which causes issues when converting the JSON into a dictionary.

Annoyingly it didn't bring up a formatting error. Here is an example of the JSON that caused the issue:

"levels" : {
    "level1": {
        ....
    },
    "level1": {
        ... << All objects should have different names. This should be called level2.
    },
    "level3": {
        ...
    }

To fix the issue I had to ensure that all objects of the same level had different names.

Answer 3

Just tested NSJSONSerialization today. With iOS 7.1. It is working. No issue found. Looks like Apple fixed the issue.

NSString* jsonString = @"{ \"freie_pl\\u00e4tze\":null}";

NSData* jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];

NSError *error = nil;
NSDictionary* jsonSerializationResult = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers|NSJSONReadingMutableLeaves error:&error];

NSLog(@"%@", jsonSerializationResult);