Getting Terminating app due to uncaught exception 'NSInvalidArgumentException' accessing a web api - ios

Question

I am trying to consume a simple web api that returns the data below in Objective C using AFJSONRequestOperation.
Results; (
{
Category = Groceries;
Id = 1;
Name = "Tomato Soup";
Price = 1;
},
{
Category = Toys;
Id = 2;
Name = "Yo-yo";
Price = "3.75";
},
{
Category = Hardware;
Id = 3;
Name = Hammer;
Price = "16.99";
}
)
My Objective-C call looks like this:
//not the real URL, just put in to show the variable being set
NSURL *url = [NSURL URLWithString:#"http://someapi"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
AFJSONRequestOperation *operation;
operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request
success: ^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
NSLog(#"Results; %#", JSON);
self.resultsArray= [JSON objectForKey:#"Results"];
}
failure: ^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error ,id JSON) {
//http status code
NSLog(#"Received Error: %d", response.statusCode);
NSLog(#"Error is: %#", error);
}
];
//run service
[operation start];
When I run my code, I can see the data returned in the NSLog statement. However I get the following error when I try to set the results to my array using the JSON objectForKey statement.
-[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0xe466510
2013-09-30 20:49:03.893 ITPMessageViewer[97459:a0b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0xe466510'
I'm fairly new to Objective-C, and can't figure out why this isn't working. Any help or ideas would be appreciated.

Answer 1

The result you are getting is an Array
objectForKey: is a NSDictionary method
So use valueForKey: which is a NSArray method.
self.resultsArray= [JSON valueForKey:#"Results"];

Answer 2

In your code, the JSON ( result ) need to follow this method to use :
self.resultsArray = (NSArray *)JSON;
It'll force the " id " type to NSArray for your self.resultsArray type ( It is an NSArray, right ? ), then you can use this method to enumerate it.
[self.resultsArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop)
{
NSDictionary *_eachResult = (NSDictionary *)obj;
[_eachResult objectForKey:#"Category"];
//...
}];
Hope it can help you.

Answer 3

I managed to update my web service to return data in a format that the AFJSONRequestOperation was happy with. This allowed me to get the JSON to parse properly. Still not sure why it needed this dictionary combo, but glad it worked.
In case anyone is writing a web api in C# to talk to objective C, this is what I did:
The update was to return the following object as JSON (code is in C#).
Dictionary > with string = "results" and the IEnumerable is my strongly typed array of objects.
public Dictionary<string, IEnumerable<Product>> GetAllProducts()
{
var sortedProuct = results.OrderBy(a => a.Category);
var proddict = new Dictionary<string, IEnumerable<Product>>()
{
{ "results", results},
};
return proddict;
}
this translates to:
Results; {
results = ({
Category = Groceries;
Id = 1;
Name = "Tomato Soup";
Price = 1;},
....