KVC

KVC 的优点是能够强制的为没有提供接口的，私有的，受保护的属性去赋值，缺点就是打破了封装性，而且不能点出属性名字，属性名容易写错，写错就崩溃。

在book类声明字段

#import <Foundation/Foundation.h>
#import "Author.h"

@interface Book : NSObject
{
    NSString * bookName;
    CGFloat    bookPrice;
    Author * bookAuthor;
    NSMutableArray * allBooks;
}
@end

在 Author 类声明字段

#import <Foundation/Foundation.h>

@interface Author : NSObject
{
    NSString * authorName;
    
}
@end

在main 函数里

#import <Foundation/Foundation.h>
#import "Book.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {

        Book * book  = [[Book alloc]init];
        Author * author = [[Author alloc]init];
        [author setValue:@"" forKey:@"authorName"];
        [book setValue:author forKey:@"bookAuthor"];
        [book setValue:@"巴金" forKeyPath:@"bookAuthor.authorName"];
        [book setValue:@"《家 * 春 * 秋》" forKey:@"bookName"];
        [book setValue:@32 forKey:@"bookPrice"];
        NSLog(@"书本名：%@  价格： %@  作者：%@",[book valueForKey:@"bookName"],[book valueForKey:@"bookPrice"],[book valueForKeyPath:@"bookAuthor.authorName"]);
        
        //设置一组书本(KVC 为数组赋值)
        NSArray * GroupBookName = [NSArray arrayWithObjects:@"《百年孤独》", @"《英雄出少年》", @"《上年包青天》", @"《围城》", @"《家和万事兴》", nil];
        NSArray * GroupBookPrice = @[@23,@32,@29,@42,@28];
        NSArray * GroupBookAuthor = @[@"莫泊桑",@"默默",@"华仔键",@"佟丽娅",@"张飞"];
        NSMutableArray * GroupBooks = [NSMutableArray arrayWithCapacity:5];
        for (int i = 0; i < GroupBookName.count; i++) {
            Book * BOOK = [[Book alloc]init];
            [BOOK setValue:GroupBookName[i] forKey:@"bookName"];
            [BOOK setValue:GroupBookPrice[i] forKey:@"bookPrice"];
            Author * author = [[Author alloc]init];
            [BOOK setValue:author forKey:@"bookAuthor"];
            [BOOK setValue:GroupBookAuthor[i] forKeyPath:@"bookAuthor.authorName"];
            [GroupBooks addObject:BOOK];
        }
        
        //kvc 为数组运算
        for (Book * oneBook in GroupBooks) {
            NSLog(@"书名：%@ 作者：%@ 价格：%@",[oneBook valueForKey:@"bookName"],[oneBook valueForKeyPath:@"bookAuthor.authorName"],[oneBook valueForKey:@"bookPrice"]);
        }
        
        [book setValue:GroupBooks forKey:@"allBooks"];
        //求平均价格
        NSLog(@"%@",[book valueForKeyPath:@"allBooks.@avg.bookPrice"]);
        //求平最高价格
        NSLog(@"%@",[book valueForKeyPath:@"allBooks.@max.bookPrice"]);
        //求最低价格
        NSLog(@"%@",[book valueForKeyPath:@"allBooks.@min.bookPrice"]);
        //求所有价格之和
        NSLog(@"%@",[book valueForKeyPath:@"allBooks.@sum.bookPrice"]);
    }
    return 0;
}