Converting NSObject to NSDictionary

Hello I a class of type NSObject:

ProductDetails *details = [[ProductDetails alloc] init];
details.name = @"Soap1";
details.color = @"Red";
details.quantity = 4;

I want to pass the "details" object to a dictionary.

I did,

NSDictionary *dict = [NSDictionary dictionaryWithObject:details forKey:@"details"];

I am passing this dict to another method which performs a check on JSONSerialization:

if(![NSJSONSerialization isValidJSONObject:dict])

And I am getting a crash on this check. Am I doing anything wrong here? I know that the details I am getting is a JSON object and I am assigning it to the properties in my ProductDetails class.

Please help me. I am a noob in Objective-C.

I now tried:

NSError* error;
NSDictionary* json = [NSJSONSerialization JSONObjectWithData:(NSData*)details options:kNilOptions error:&error];

All I need here is an easy way to convert details to NSData.

I noticed that I have an array inside my object may be thats why all the ways I tried is throwing an exception. However since this question is becoming to big, I have started an another question thread for it where I have displayed the data I am getting inside the object - https://stackoverflow.com/questions/19081104/convert-nsobject-to-nsdictionary

NSDictionary *details = {@"name":product.name,@"color":product.color,@"quantity":@(product.quantity)};

NSError *error; 
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:details 
                                                   options:NSJSONWritingPrettyPrinted // Pass 0 if you don't care about the readability of the generated string
                                                     error:&error];

if (! jsonData) {
    NSLog(@"Got an error: %@", error);
} else {
    NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
}

Second part's source: Generate JSON string from NSDictionary in iOS