I am using JSONKit to parse JSON string into NSDictionary:
NSDictionary *deserializedData = [jsonString objectFromJSONString];
My question is: how can I change the dictionary values and get a changed JSON String?
I've tried to change the dictionary values:
[deserializedData setObject:[NSNumber numberWithInt:iRatings] forKey:@"ratings"];
But the app crashes in that line. What am I doing wrong?
Thanks in advance!
While the other answers are correct, what you really want in this case is:
NSMutableDictionary *deserializedData = [jsonString mutableObjectFromJSONString];
The mutableObjectFromJSONString method will create a mutable dictionary directly, which saves time and memory.
//
// we begin with our string in json format
//
NSString *jsonString = [[NSString alloc] initWithString:@"{\"1\":\"Hole 1: Rossy Robinson - $25\",\"2\":\"Hole 7: Davey Ambrose - $25\",\"3\":\"Hole 14: Ross Robinson - $25\"}"];
//
// convert the json string to an NSMutableDictionary
//
NSError *e;
NSMutableDictionary *JSONdic = [NSJSONSerialization JSONObjectWithData: [jsonString dataUsingEncoding: NSUTF8StringEncoding] options: NSJSONReadingMutableContainers error: &e];
//
// change a value and add a new value in the dict
//
NSLog(@"before: object for key 1 is: %@", [JSONdic objectForKey:@"1"]);
[JSONdic setObject:@"xxx" forKey:@"1"];
[JSONdic setObject:@"Phil McQuitty" forKey:@"2"];
//
//convert dictionary object to json data
//
NSData* jsonData = [NSJSONSerialization dataWithJSONObject:JSONdic options:NSJSONWritingPrettyPrinted error:&e];
//
// convert the json data back to a string
//
NSString *jsonText = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];\
//
// print out the final results
//
NSLog(@"back to string: %@", jsonText);
NSDictionary is an immutable dictionary, you need NSMutableDictionary to change the data. I'm not sure about JSONKit, but the built-in Cocoa JSON parser has a flag to return the data in mutable containers.
In worst case, you can do something like that:
NSMutableDictionary* data = [NSMutableDictionary dictionaryWithDictionary:[jsonString objectFromJSONString]];
[data setObject:[NSNumber numberWithInt:iRatings] forKey:@"ratings"];
You try to change an immutableobject.
NSMutableDictionary *deserializedData = [NSMutableDictionary dictionaryWithDictionary: [jsonString objectFromJSONString]];
This is a mutable dictionary and you can change the values in it.
You try like this:
NSMutableDictionary *deserializedData = [NSMutableDictionary dictionaryWithDictionary: [jsonString objectFromJSONString]];
and then change the values:
[deserializedData setObject:[NSNumber numberWithInt:iRatings] forKey:@"ratings"];
For NSDictionary we cannot add or change values, thats why application is crashing.
