Parsing JSON response - ios

Question

I am using AFJSONRequestOperation to request a remote API:
NSURLRequest *request = [NSURLRequest requestWithURL:url];
AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
//Remove the SVProgressHUD view
[SVProgressHUD dismiss];
//Check for the value returned from the server
NSData *jsonData = [JSON dataUsingEncoding:NSUTF8StringEncoding];//This line cause crash
NSArray *arr = [NSJSONSerialization JSONObjectWithData:jsonData
options:0
error:nil];
loginDic=[[NSDictionary alloc]init];
loginDic=[arr objectAtIndex:0];
NSLog(#"%#",loginDic);
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
NSLog(#"Request Failed with Error: %#", [error.userInfo objectForKey:#"NSLocalizedDescription"]);
}];
[operation start];
[SVProgressHUD showWithStatus:#"Loading"];
However, the app crashes and I am getting this error:
[__NSCFDictionary dataUsingEncoding:]: unrecognized selector sent to instance
Here is an NSLog for the JSON object returned:
Result = (
{
operation = 5;
result = 1;
}
);
Am I missing something, because I think that I am not parsing correctly the JSON object. Please correct me.

Answer 1

It looks like AFJSONRequestOperation is deserializing JSON to a dictionary for you, and then you're trying to do it again. JSON is an NSDictionary but you're calling an NSString method.
Remove all of this code:
NSData *jsonData = [JSON dataUsingEncoding:NSUTF8StringEncoding];//This line cause crash
NSArray *arr = [NSJSONSerialization JSONObjectWithData:jsonData
options:0
error:nil];
loginDic=[[NSDictionary alloc]init];
loginDic=[arr objectAtIndex:0];
And replace it with:
loginDic = [[JSON objectForKey:#"Result"] lastObject];
(That'll work safely without checking array bounds, but assumes that there's only one element in the array.)

Answer 2

The object you get in the success block is already parsed by AFJSONRequestOperation.
In your case you get a NSDictionary object.
You can check the class of the object using the isKindofClass-method:
if ([JSON isKindOfClass:[NSDictionary class]]) {
NSDictionary* dict = (NSDictionary*)JSON;
...
}