NSDictionary throws exception not logical for me - ios

Question

Good day.Im requesting to some server and defiantly I'm having some JSON data there so I'm trying to parse it.Im stuck at the point where I'm actually parsing it.So i have method called parseJson which requires NSDictionry as parameter so here how it looks
-(void)parseJson:(NSDictionary*)jsonData{
[jsonData valueForKey:#"email"];
}
as you can see not much here but I'm getting exeption when the code reaches at
[jsonData valueForKey:#"email"];
I have pretty much started developing for iOS from yesterday and the exception is hell as weird for me which is the next.
this class is not key value coding-compliant for the key email.'
So by googling i found nothing...and pretty much in every JSON PARSING tutorial this one line code is written so I'm very much confused what does this exception means....Please help,what am i doing wrong?
FULL REQUEST CODE
-(void) makeRequest{
// Create the request.
__block NSString *returnResponse = #"hello";
NSURLSessionConfiguration *defaultConfigObject = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration: defaultConfigObject delegate: nil delegateQueue: [NSOperationQueue mainQueue ]];
//Create an URLRequest
NSURL *url = [NSURL URLWithString:#"http://jsonplaceholder.typicode.com/posts"];
NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url];
//Create POST Params and add it to HTTPBody
NSString *params = #"api_key=APIKEY&email=example#example.com&password=password";
[urlRequest setHTTPMethod:#"POST"];
[urlRequest setHTTPBody:[params dataUsingEncoding:NSUTF8StringEncoding]];
//Create task
NSURLSessionDataTask * dataTask =[defaultSession dataTaskWithRequest: urlRequest completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if(response!=NULL){
returnResponse =[NSString stringWithFormat:#"%#",response];
}else{
returnResponse = [NSString stringWithFormat:#"%#",error.description];
}
[self hideSpinner];
NSString* jsonString = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
[self parseJson:jsonString];
}];
[dataTask resume];
}
Ok i have changed the method now to
-(void)parseJson:(NSString*)jsonData{
NSDictionary * dictionary = [[NSDictionary alloc] initWithContentsOfFile:jsonData];
NSLog(#"%#",jsonData);
NSString* mystring = [dictionary valueForKey:#"email"];
NSLog(#"%#",mystring);
}
and here is the output i get when logging the strings
2016-01-22 00:25:48.690 testproject[627:83537] {
"api_key": "APIKEY",
"email": "example#example.com",
"password": "password",
"id": 101
}
2016-01-22 00:25:48.690 testproject[627:83537] (null)
As you can see the exception problem gone,but now i get NULL value..but you can see that just a one line above i got my son with email key string....so i have fully no clue whats going on.

Answer 1

valueForObject:method has nothing to do with NSDictionary. It is used by KVO which stands for Key-Value Observing. You can retrieve object from NSDictionary by using [] or objectForKey: method. Here are the examples:
dictionary[#"email"]
//or
[dictionary objectForKey:#"email"]
//EDITED
Instead of converting NSObject to NSString and trying accessing properties with KVO or dictionary methods/syntax please try to parse NSData using the code below:
NSDictionary *JSONDictionary =[NSJSONSerialization JSONObjectWithData:data options:0 error:nil]
NSString *email = JSONDictionary[#"email"];
You should be able to retrieve objects from the JSONDictionary using methods/syntax mentioned by me in the first version of the answer.