complex JSON parsing using Objective-C

Question

{
   "Flight1":{
      "3":{
         "id":"10",
         "name":"JumboJet1B",
         "level":"1",
         "category":"1",
         "energy":"10",
         "bonus":"10",
         "completed":0
      },
      "4":{
         "id":"10",
         "name":"JumboJet1B",
         "level":"1",
         "category":"1",
         "energy":"10",
         "bonus":"10",
         "completed":0
      }
   }
}

This was the json output

How can I parse inside the items of 3 and 4, say getting the id, energy and name

Thanks!

score 1 · Accepted Answer · 2011-04-20 05:38:51Z

If the order inside Flight1 doesn’t matter, the following should work:

NSDictionary *flights = … // result from a JSON parser
NSDictionary *flight1 = [flights objectForKey:@"Flight1"];

for (NSString *key in [flight1 allKeys]) {
    NSDictionary *flight1Entry = [flight1 objectForKey:key];

    NSString *entryId = [flight1Entry objectForKey:@"id"];
    NSString *entryName = [flight1Entry objectForKey:@"name"];
    NSString *entryEnergy = [flight1Entry objectForKey:@"energy"];

    …
}

Otherwise, if you want the keys sorted according to their numeric value:

NSDictionary *flights = … // result from a JSON parser
NSDictionary *flight1 = [flights objectForKey:@"Flight1"];
NSArray *flight1Keys = [[flight1 allKeys] sortedArrayUsingComparator:^(id o1, id o2) {
    NSInteger i1 = [o1 integerValue];
    NSInteger i2 = [o2 integerValue];
    NSComparisonResult result;

    if (i1 > i2) result = NSOrderedDescending;
    else if (i1 < i2) result = NSOrderedAscending;
    else result = NSOrderedSame;

    return result;
}];

for (NSString *key in flight1Keys) {
    NSDictionary *flight1Entry = [flight1 objectForKey:key];

    NSString *entryId = [flight1Entry objectForKey:@"id"];
    NSString *entryName = [flight1Entry objectForKey:@"name"];
    NSString *entryEnergy = [flight1Entry objectForKey:@"energy"];

    …
}

Nick Weaver · Accepted Answer · 2011-04-19 10:15:09Z

0

Assuming that you are using the json framework you could access it like this:

NSDictionary *jsonDict = [jsonString JSONValue];

NSString *id = [[[jsonDict objectForKey:@"Flight1"] objectForKey:@"3"] objectForKey:@"id"];

This assumes alot, so make use of try except blocks or iterate through the different levels.

answered Apr 19, 2011 at 10:15

Nick Weaver

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5 Comments

user715626 Over a year ago

Mr. Weaver I appreciate your answer but the thing is what if the keys 3,4 are dynamic they can change to 1,6,9,12,22 and so on. How can you parse it knowing only the key "Flight1"?

tidwall Over a year ago

Use valueForKey: instead of objectForKey: and you won't have to worry about try except blocks.

user557219 Over a year ago

@jojaba What?! -objectForKey: is the method defined in NSDictionary to return an object for a given key. It won’t throw an exception if a key doesn’t exist — it simply returns nil in this case.

Nick Weaver Over a year ago

@Delta Boy your question asked for a way to retrieve the desired information. I actually hinted that you may want to iterate through the different levels. It's still your json structure, so your parser has to adapt to it. So if you'd like to parse the first two level use fast enumeration, which is available in dictionaries and arrays.

tidwall Over a year ago

@Batarious The JSON library specified by Nick returns NSString, NSNumber, NSArray and NSDictionary. -valueForKey: works on ANY class while -objectForKey: does not.

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