KVC機制

The NSKeyValueCoding informal protocol defines a mechanism by which you can access the properties of an object indirectly by name (or key), rather than directly through invocation of an accessor method or as instance variables. Thus, all of an object’s properties can be accessed in a consistent manner.

void changeName(Person *p, NSString *newName)

{

    // using the KVC accessor (getter) method

    NSString *originalName = [p valueForKey:@"name"];

    // using the KVC  accessor (setter) method.

    [p setValue:newName forKey:@"name"];

    NSLog(@"Changed %@'s name to: %@", originalName, newName);

}