Objective C - Issue when read JSON Key - ios

Question

Hi everyone I am working with a JSON file in my xCode project.
I can easily display the various JSON key but when I call a key it specifies my app crashes and I don't understand why ...
I was very careful to write the keys correctly but it keeps crashing ...
This is my example JSON file
{
"Università" : {
"uniID" : {
"latitudine" : 43.115441,
"longitudine" : 12.389587,
"nome" : "Università per stranieri di Perugia",
"regione" : "Umbria"
},
"uniID" : {
"latitudine" : 41.860348,
"longitudine" : 12.496308,
"nome" : "Università degli Studi Internazionali di Roma ( UNINT )",
"regione" : "Lazio"
},
}
}
When I try to recover the "name" key my app crashes, this is true even if I call "latitude" or "longitude" etc ...
Where am I doing wrong ?
These are the functions I use for reading the JSON file
-(void)setupUniversityLocation:(MKMapView *)mapView {
NSDictionary *dict = [self JSONUniversity];
NSArray *universityArray = [[dict objectForKey:#"Università"] objectForKey:#"uniID"];
for (NSDictionary *uni in universityArray) {
NSString *uniname = [uni objectForKey:#"nome"];
NSLog(#"uniname %#",uniname);
}
}
#pragma mark - Read JSON Data University
-(NSDictionary *)JSONUniversity {
NSString *path = [[NSBundle mainBundle] pathForResource:#"university" ofType:#"json"];
NSData *data = [NSData dataWithContentsOfFile:path];
return [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
}
I also wanted to ask you how can I directly read the keys "name", "latitude" etc ... without where to invoke the "uniID" key? is it possible to bypass a category key?

Answer 1

There is no array in your json file. You should change json file to
{
"Università" : [
{
"latitudine" : 43.115441,
"longitudine" : 12.389587,
"nome" : "Università per stranieri di Perugia",
"regione" : "Umbria"
},
{
"latitudine" : 41.860348,
"longitudine" : 12.496308,
"nome" : "Università degli Studi Internazionali di Roma ( UNINT )",
"regione" : "Lazio"
}
]
}
Use [] to present array instead of {} and below code will work
-(void)setupUniversityLocation:(MKMapView *)mapView {
NSDictionary *dict = [self JSONUniversity];
NSArray *universityArray = [dict objectForKey:#"Università"];
for (NSDictionary *uni in universityArray) {
NSString *uniname = [uni objectForKey:#"nome"];
NSLog(#"uniname %#",uniname);
}
}
#pragma mark - Read JSON Data University
-(NSDictionary *)JSONUniversity {
NSString *path = [[NSBundle mainBundle] pathForResource:#"university" ofType:#"json"];
NSData *data = [NSData dataWithContentsOfFile:path];
return [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
}

Answer 2

There is no Array in the example JSON you posted.
So in this line:
NSArray *universityArray = [[dict objectForKey:#"Università"] objectForKey:#"uniID"];
When you are assuming the output is an array, in actuality it's a dictionary.
If you put a log statement outputting the kind of class returned after that line:
NSLog(#"Kind of class returned from univeristyArray = %#", [universityArray class]);
It will return:
Kind of class returned from univeristyArray = __NSDictionaryI
Right now your structure of the JSON example you posted is:
Top Level Object (Dictionary)
"Università" (Dictionary)
"uniID" (Dictionary)
Another issue with this structure is that you have multiple values for the same key under the "Università" dictionary (i.e. multiple "uniID" which have different associated values)
If you have control over the JSON generated, you have a couple of different options depending on what you're attempting to do:
From your code, it looks like you're attempting to loop through all the "Università" and output their name -- and you're expecting them to be stored in an Array. In this case you'd want to change the "Università" data structure to an Array in the JSON.
Alternatively, make the "nome" value of the university the key for the lower level dictionaries and then fetch them by name (only if the universities names are going to be unique) -- this would be good if you have a large list of universities and you're attempting to only fetch specific ones (by name).
Example of #1:
university.json:
{
"Università" : [
{
"latitudine" : 43.115441,
"longitudine" : 12.389587,
"nome" : "Università per stranieri di Perugia",
"regione" : "Umbria"
},
{
"latitudine" : 41.860348,
"longitudine" : 12.496308,
"nome" : "Università degli Studi Internazionali di Roma ( UNINT )",
"regione" : "Lazio"
},
]
}
setupUniversityLocation:
-(void)setupUniversityLocation {
NSDictionary *dict = [self JSONUniversity];
NSArray *universityArray = [dict objectForKey:#"Università"];
for (NSDictionary *uni in universityArray) {
NSString *uniname = [uni objectForKey:#"nome"];
NSLog(#"uniname %#",uniname);
}
}
Example of #2:
university.json:
{
"Università" : {
"Università per stranieri di Perugia": {
"latitudine" : 43.115441,
"longitudine" : 12.389587,
"regione" : "Umbria"
},
"Università degli Studi Internazionali di Roma ( UNINT )": {
"latitudine" : 41.860348,
"longitudine" : 12.496308,
"regione" : "Lazio"
},
}
}
setupUniversityLocation:
-(void)setupUniversityLocation {
NSDictionary *dict = [self JSONUniversity];
NSDictionary *universityDictionary = [dict objectForKey:#"Università"];
// this is an example of looping through the entire dictionary
// typically you'd use objectForKey when accessing a specific university
for (NSString *universityNameKey in universityDictionary.allKeys) {
NSDictionary *specificUniDictionary = [universityDictionary objectForKey:universityNameKey];
NSLog(#"uniname %#",universityNameKey);
NSLog(#"latitudine %#", [specificUniDictionary objectForKey:#"latitudine"]);
NSLog(#"longitudine %#", [specificUniDictionary objectForKey:#"longitudine"]);
}
}
For most cases I would recommend going with the second option as if it's a large list it's going to be a lot quicker to find a specific item, but it definitely depends on your use case.