kvc（键-值编码）
{ NSString *_name;
Author *_author;
NSArray *_kvcArray;
float price;}
//kvc,setValue 的设的值是 “要设置的值” forKey 设置的是对象的属性,如果不是的话要将其转化对象（int folat,char,double）
Book *book = [[Book alloc] init];
// Author *author = [[Author alloc] init];
// [author setValue:@"jack" forKey:@"aname"];
//
// //间接访问
// [book setValue:@"ipa set Value" forKey:@"name"];
// [book setValue:author forKey:@"author"];
//
// //路径访问
// [book setValue:@"tom" forKeyPath:@"author.aname"];
// NSString *authorName = [book valueForKeyPath:@"author.aname"];
//
//一对多访问
NSMutableArray *mutableArray = [NSMutableArray arrayWithCapacity:3];
for (int i = 0; i < 3; i++) {
Book *book = [[Book alloc] init];
NSString *string = [NSString stringWithFormat:@"job_%d",i];
[book setValue:@(12+i) forKey:@"price"];
[book setValue:string forKey:@"name"];
[mutableArray addObject:book];
[book release];
}
// [book setValue:mutableArray forKey:@"_kvcArray”];
//
// NSArray *bookArray = [book valueForKeyPath:@"_kvcArray.name”];//通过数组的中的属性名路径访问，体现了键值访问
//上面这种访问相当于这种
// NSArray *bookArray = [mutableArray valueForKeyPath:@“_name”];//这也是对mutableArray 的属性进行路劲访问
//
// NSLog(@"bookArray:%@",bookArray);
//
// NSLog(@"%@",authorName);
//运算 avg sum count min max,运算的必须是NSNumber 和 数据类型，返回值是NSNumber, setValue 时，引用计数会加1
[book setValue:mutableArray forKey:@"_kvcArray”];//将book 的 _kvcArray属性设值
NSNumber *sum = [book valueForKeyPath:@"_kvcArray.@sum.price”];//格式是(属性.@运算方式.属性对象中的属性）//使用运算符的前提是 NSNumber 的数据类型
NSLog(@"sum : %@",sum);