How do I traverse a multi dimensional NSArray? - objective-c

Question

I have array made from JSON response.
NSLog(#"%#", arrayFromString) gives the following:
{
meta = {
code = 200;
};
response = {
groups = (
{
items = (
{
categories = (
{
icon =
"http://foursquare.com/img/categories/parks_outdoors/default.png";
id = 4bf58dd8d48988d163941735;
and so on...
This code
NSArray *arr = [NSArray arrayWithObject:[arrayFromString valueForKeyPath:#"response.groups.items"]];
gives array with just one element that I cannot iterate through. But if I write it out using NSLog I can see all elements of it.
At the end I would like to have an array of items that I can iterate through to build a datasource for table view for my iPhone app.
How would I accomplish this?
EDIT:
I have resolved my issue by getting values from the nested array (objectAtIndex:0):
for(NSDictionary *ar in [[arrayFromString valueForKeyPath:#"response.groups.items"] objectAtIndex:0]) {
NSLog(#"Array: %#", [ar objectForKey:#"name"]);
}

Answer 1

First, the data structure you get back from the JSON parser is not an array but a dictionary: { key = value; ... } (curly braces).
Second, if you want to access a nested structure like the items, you need to use NSObject's valueForKeyPath: method. This will return an array of all items in your data structure:
NSLog(#"items: %#", [arrayFromString valueForKeyPath:#"response.groups.items"]);
Note that you will loose the notion of groups when retrieving the item objects like this.

Answer 2

Looking at the JSON string you posted, response.groups.items looks to be an array containing one item, a map/dictionary containing one key, "categories." Logging it out to a string is going to traverse the whole tree, but to access it programmatically, you have to walk the tree yourself. Without seeing a more complete example of the JSON, it's hard to say exactly what the right thing to do is here.
EDIT:
Traversing an object graph like this is not that simple; there are multiple different approaches (depth-first, breadth-first, etc,) so it's not necessarily something for which there's going to be a simple API for you to use. I'm not sure if this is the same JSON library that you're using, but, for instance, this is the code from a JSON library that does the work of generating the string that you're seeing. As you can see, it's a bit involved -- certainly not a one-liner or anything.
You could try this, which I present without testing or warranty:
void __Traverse(id object, NSUInteger depth)
{
NSMutableString* indent = [NSMutableString string];
for (NSUInteger i = 0; i < depth; i++) [indent appendString: #"\t"];
id nextObject = nil;
if ([object isKindOfClass: [NSDictionary class]])
{
NSLog(#"%#Dictionary {", indent);
NSEnumerator* keys = [(NSDictionary*)object keyEnumerator];
while (nextObject = [keys nextObject])
{
NSLog(#"%#\tKey: %# Value: ", indent, nextObject);
__Traverse([(NSDictionary*)object objectForKey: nextObject], depth+1);
}
NSLog(#"%#}", indent);
}
else if ([object isKindOfClass: [NSArray class]])
{
NSEnumerator* objects = [(NSArray*)object objectEnumerator];
NSLog(#"%#Array (", indent);
while (nextObject = [objects nextObject])
{
__Traverse(nextObject, depth+1);
}
NSLog(#"%#)", indent);
}
else
{
NSLog(#"%#%#",indent, object);
}
}
void Traverse(id object)
{
__Traverse(object, 0);
}