kvc原来是 其它技术的基础，

kvc 是kvo的基础，是core data的基础，并不是说 单纯kvc比 直接用.访问好处多了多少，
NSManagedObject *character; //Lets assume the core data object has been fetched.

//Giving the object some values to save later.
[character setValue:@"Sakura Kinomoto" forKey:@"characterName"];
[character setValue:38 forKey:@"ownedCards"];

//Fetching those values using KVC.

NSString *sakura = [character valueForKey:@"characterName"];
NSInteger numberOfClowCards = [character valueForKey:@"ownedCards"];

 Key-value coding is a fundamental technology when working with key-value observing, Cocoa bindings, Core Data, and making your application AppleScript-able. You are expected to be familiar with the basics of Cocoa development and the Objective-C language.