How to parse JSON dynamically in iOS

Question

We used a third party service and it provides a JS file. The js file launches an http request and get a json.We parsed the json and got the content we wanted but the json format

Answer 1

For this purpose we looked at Cocoa's standard key path infrastructure but weren't particularly happy with how it combines with arrays and dictionaries. In the end I ended up writing my own little key-path lookup thing, essentially like:

- (id)objectAtPath:(NSString *)path inObject:(id)object
{
    // accept an input string like key1.key2.key3.index.key4.etc;
    // so we'll split on the dots and use each separate component
    // to navigate the object graph
    NSString *components = [path componentsSeparatedByString:@"."];
    for(NSString *component in components)
    {
         if([object isKindOfClass:[NSDictionary class]])
         {
             // if this is a dictionary, use this component as
             // a key into the dictionary
             object = [object objectForKey:component];
         }
         else
             if([object isKindOfClass:[NSArray class]])
             {
                 // if this is an array, use this component
                 // as an index into the array
                 NSInteger index = [component integerValue];

                 // treat out of bounds indices as finding nil
                 // rather than raising an exception
                 if(index < 0 || index >= [object count]) object = nil;
                 else object = [object objectAtIndex:index];
             }
    }
}

So you might call objectAtPath:@"shoes.4.typeOfLaces" inObject:jsonResult if 'jsonResult' is a dictionary to get the array 'shoes', the dictionary at index 4 in the array and then whatever value that dictionary has for the key 'typeOfLaces'.

The production code actually has some smarter navigation aids, allowing you to say things like "take whichever object in this array of dictionaries has the largest value for the key 'size'" or "take the object with type=large if it exists, otherwise take any object", but exactly what you want to do there will depend on your app and the variability of the schema.

Once you're navigating object graphs by key path, you can just grab the current key paths from a server somewhere, allowing you to change how JSON is navigated on device without submitting a new binary.

The only warning I'd add is to be careful how much functionality you put into your key paths. Apple don't allow fresh code to be downloaded so whatever you do you don't want to end up at anything that Apple could construe as a scripting language, no matter how restricted.