来自JSON的NSData提取的奇怪响应

Question

Trying to fetch value from json, response string showing correct fetched data, but when NSData convert and put it in to NSDictionary, two values get interchanged. Below is code tried.

 +(NSMutableDictionary *)seatMap:(NSDictionary *)seatId eventId:(NSDictionary *)eid
 {
 NSString *urlStr = [NSString stringWithFormat:@"http://met.co/api/seatmap/%@/%@",   [seatId valueForKey:@"sid"], [eid valueForKey:@"eid"]];

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:
                                [NSURL URLWithString:
                                 [urlStr stringByAddingPercentEscapesUsingEncoding:
                                  NSUTF8StringEncoding]]];
//NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString:urlStr]];

NSString *responseString = [MetApi sendRequest:request];
NSLog(@"response:%@", responseString);
NSError *error;
NSData *jsonData = [responseString dataUsingEncoding:NSUTF16StringEncoding];
NSDictionary *results = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:&error];

//NSDictionary *results = [responseString JSONValue];
NSMutableDictionary *dict = [[NSMutableDictionary alloc]initWithDictionary:results];
NSLog(@"dict in API-------------%@",dict);

return dict;
}

Above code giving this output

        1 = off;
        10 = off;
        2 = on;
        3 = on;
        4 = on;
        5 = on;
        6 = on;
        7 = on;
        8 = on;
        9 = on;

But it should

1: "off",
2: "on",
3: "on",
4: "on",
5: "on",
6: "on",
7: "on",
8: "on",
9: "on",
10: "off"

json file

{
row1: {
1: "on",
2: "on",
3: "on",
4: "on",
5: "on",
6: "on",
7: "on",
8: "on",
9: "on",
10: "on",
attr: {
total: "10",
type: "Gold"
}
},
row2: {
1: "off",
2: "on",
3: "on",
4: "on",
5: "on",
6: "on",
7: "on",
8: "on",
9: "on",
10: "off",
attr: {
total: "10",
type: "Gold"
}
}
}
}

Why this interchange of data happening. Please guide for the above, if anything not clear please ask. Thanks in advance.

Answer 1

Your JSON contains only dictionaries and dictionaries do not maintain order. In other words, the order of elements when you print a dictionary is entirely implementation specific and may even be random.

If order is relevant, you have to use lists (eg [1,2,3] )

For example, you could use the following JSON

{ "rows":
  [ { "values":["on", "on", "on", "on", "on", "on", "on", "on", "on", "on"]
    , "attr": { "total": 10
              , "type": "Gold"
              }
    }
,   { "values":["off", "on", "on", "on", "on", "on", "on", "on", "on", "off"]
    , "attr": { "total": 10
              , "type": "Gold"
              }
    }
  ]
}

If you don't want to change your JSON and get the values, say of row1 in order you could use the following snippet (not recommended, if order is important, use a list!):

/* expects `NSDictionary *dict` as defined in the code of your question. Code is untested but should give you the idea... */
NSInteger max = [dict[@"row1"][@"attr"][@"total"] intValue];

for (int i=1; i<= max; i++) {
    NSLog("value %ld = '%@'", i, dict[@"row1"][@"attr"][[NSString stringWithFormat:@"%d",i]]);
}

Answer 2

In NSDictionary key value pairs matters not its order in appearence

You can get the value using objectForKey: method even if the order is changed