Pulling Data from an NSDictionary - ios

Question

So I have an NSDictionary that has a variety of data within it. When printed to the log, it prints like this:
[{"user_id":3016817,"grade":"A","percent":"93","grading_periods":[{"assignments":[{"points":100.0,"grade":"A","score":95.0,"percent":"93","comment":null,"id":3268180},{"points":100.0,"grade":"A","score":90.0,"percent":"93","comment":null,"id":3268181}],"grade":"A","percent":"93","name":"Default"}]},{"user_id":3016818,"grade":"A","percent":"94","grading_periods":[{"assignments":[{"points":100.0,"grade":"A","score":92.0,"percent":"94","comment":null,"id":3268180},{"points":100.0,"grade":"A","score":95.0,"percent":"94","comment":null,"id":3268181}],"grade":"A","percent":"94","name":"Default"}]}]
If I use a formatter online, its a lot more readable and looks something like this:
[
{
"user_id": 3016817,
"grade": "A",
"percent": "93",
"grading_periods": [
{
"assignments": [
{
"points": 100,
"grade": "A",
"score": 95,
"percent": "93",
"comment": null,
"id": 3268180
},
{
"points": 100,
"grade": "A",
"score": 90,
"percent": "93",
"comment": null,
"id": 3268181
}
],
"grade": "A",
"percent": "93",
"name": "Default"
}
]
},
{
"user_id": 3016818,
"grade": "A",
"percent": "94",
"grading_periods": [
{
"assignments": [
{
"points": 100,
"grade": "A",
"score": 92,
"percent": "94",
"comment": null,
"id": 3268180
},
{
"points": 100,
"grade": "A",
"score": 95,
"percent": "94",
"comment": null,
"id": 3268181
}
],
"grade": "A",
"percent": "94",
"name": "Default"
}
]
}
]
My question would be how would I access the value of grade or score for a specific user_id using this dictionary?

Answer 1

Your string represents a NSArray, not a NSDictionary. And it's a JSON string, so you can parse it using NSJSONSerialization:
NSString *jsonString = #"..." // your string here
// Create array from json string
NSArray *jsonArray = [NSJSONSerialization
JSONObjectWithData:[jsonString dataUsingEncoding:NSUTF8StringEncoding]
options:NSJSONReadingMutableContainers
error:Nil];
// Loop to find your user_id
// Because each child of this array is a dictionary
for (NSDictionary *dic in jsonArray) {
if ([dic[#"user_id"] isEqual:#3016817]) { // user_id field is number
// Access what you want
NSString *grade = dic[#"grade"];
// For "score" you must go deeper
// Just remember, [] is array and {} is dictionary
}
}

Answer 2

A simple way to do this would be
for (NSDictionary* d in theArray) {
if ([d[#"user_id"] isEqualToString: u]) {
// do something
}
}
And matt is right, it is an array of dictionaries, no matter what type you declared to be.

Answer 3

You can use below class method of NSJsonSerialization class to create NSArray which will contain all the dictionaries.
+ (id)JSONObjectWithData:(NSData *)data options:(NSJSONReadingOptions)opt error:(NSError **)error;
Once you get the array of dictionaries from JSON, you can do following:
NSArray *filteredjsonArr = [jsonArr filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:#"user_id == %#", #"3016818"]];
NSDictionary *dict = [filtered firstObject];
if (dict != nil) {
NSString *grade = [dict objectForKey:#"grade"];
NSArray *gradingPeriods = [dict objectForKey:#"grading_periods"];
}
To access score and grade for specific assignments, you'll need to drill down further into gradingPeriods array.