OC KVC总结

　　在iOS开发中，我们一般使用set方法或者点语法来修改对象的属性值，比如说 stu.age = 9 与 [stu setAge:9]。

　　KVC（key value coding）键值编码，这是一种间接修改对象属性值的方法。实现方法就是通过用字符串来描述要修改的属性。基本的操作方法有 setValue:forKey: 和 valueForKey,以字符串的形式发送对象

　　特别提醒，使用KVC中所有的value都必须是对象。

      在此以Student类和 Book类作为例子来总结

　　Student类：

//.h文件
#import <Foundation/Foundation.h>
@class Book;
@interface Student : NSObject

@property (nonatomic, assign) int age;

@property (nonatomic, copy) NSString* name;


@property (nonatomic, strong) Book* book;

@property (nonatomic, strong) NSArray* books;
@end

//.m文件

#import "Student.h"
#import "Book.h"
@implementation Student


- (NSString *) description
{
    return  [NSString stringWithFormat:@"%@ %d", _name, _age];
}
@end

　　Book类：

　　

//.h文件
#import <Foundation/Foundation.h>

@interface Book : NSObject


@property (nonatomic, assign) int price;
@end

//.m文件
#import "Book.h"

@implementation Book

@end

　　主函数：

　　

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


//1.设值 取值
void fun1()
{
    NSLog(@"==============fun1==============");
    Student *stu = [[Student alloc] init];
    
    [stu setValue:@"hehe" forKey:@"name"];
    [stu setValue:@10 forKey:@"age"];
    
    NSLog(@"%@", stu);
    
    NSLog(@"name : %@", [stu valueForKey:@"name"]);
}

//2.批量获取属性值
void fun2()
{
    NSLog(@"==============fun2==============");
    Student *stu = [[Student alloc] init];
    
    [stu setValue:@"hehe" forKey:@"name"];
    [stu setValue:@10 forKey:@"age"];
    
    NSArray *arr = @[@"name", @"age"];
    
    NSDictionary  *dict = [stu dictionaryWithValuesForKeys:arr];
    
    NSLog(@"%@", dict);
}

//3.批量设置属性值（通过字典批量赋值）
void fun3()
{
    NSLog(@"==============fun3==============");
    Student *stu = [[Student alloc] init];
    
    NSDictionary *dict = @{@"age": @12, @"name" : @"悟空"};
    
    [stu setValuesForKeysWithDictionary:dict];
    
    NSLog(@"%@", stu);
}


//4.通过键路径(key path)访问（使用valueForKeyPath）
void fun4()
{
    NSLog(@"==============fun4==============");
    Student *stu = [[Student alloc] init];
    Book *book = [[Book alloc] init];
    stu.book = book;
    //设置值
    [stu setValue:@12 forKeyPath:@"book.price"];
    //获取值
    NSNumber *price = [stu valueForKeyPath:@"book.price"];
    
    NSLog(@"price: %@", price);
}

//5.对数组进行整体操作
void fun5()
{
    NSLog(@"==============fun5==============");
    Student *stu = [[Student alloc] init];
    
    Book *book = [[Book alloc] init];
    book.price = 12;
    Book *book1 = [[Book alloc] init];
    book1.price = 10;
    Book *book2 = [[Book alloc] init];
    book2.price = 12;
    
    NSArray *arr = @[book, book1, book2];
    
    stu.books = arr;
    //获取值
//    NSArray *prices = [stu valueForKeyPath:@"books.price"];
    NSArray *prices = [stu.books valueForKeyPath:@"price"];
    NSLog(@"prices: %@", prices);
}

//6.键路径的运算符（数组元素求和）
void fun6()
{
    NSLog(@"==============fun6==============");
    Student *stu = [[Student alloc] init];
    
    Book *book = [[Book alloc] init];
    book.price = 12;
    Book *book1 = [[Book alloc] init];
    book1.price = 10;
    Book *book2 = [[Book alloc] init];
    book2.price = 12;
    
    NSArray *arr = @[book, book1, book2];
    
    stu.books = arr;
    //获取值
    NSNumber *sum = [stu valueForKeyPath:@"books.@sum.price"];
    NSLog(@"prices: %@", sum);
}

//7.键路径的运算符（数组总数count）
void fun7()
{
    NSLog(@"==============fun7==============");
    Student *stu = [[Student alloc] init];
    
    Book *book = [[Book alloc] init];
    book.price = 12;
    Book *book1 = [[Book alloc] init];
    book1.price = 10;
    Book *book2 = [[Book alloc] init];
    book2.price = 12;
    
    NSArray *arr = @[book, book1, book2];
    
    stu.books = arr;
    //获取值
    NSNumber *sum = [stu valueForKeyPath:@"books.@count.price"];
    NSLog(@"num: %@", sum);
}

//8.键路径的运算符（获取数组不同元素）
void fun8()
{
    NSLog(@"==============fun8==============");
    Student *stu = [[Student alloc] init];
    
    Book *book = [[Book alloc] init];
    book.price = 12;
    Book *book1 = [[Book alloc] init];
    book1.price = 10;
    Book *book2 = [[Book alloc] init];
    book2.price = 12;
    
    NSArray *arr = @[book, book1, book2];
    
    stu.books = arr;
    //获取值
    NSArray *array = [stu valueForKeyPath:@"books.@distinctUnionOfObjects.price"];
    NSLog(@"array: %@", array);
}

//9.求数组元素中得最大值、最小值、平均值
void fun9()
{
    NSLog(@"==============fun9==============");
    Student *stu = [[Student alloc] init];
    
    Book *book = [[Book alloc] init];
    book.price = 12;
    Book *book1 = [[Book alloc] init];
    book1.price = 10;
    Book *book2 = [[Book alloc] init];
    book2.price = 12;
    
    NSArray *arr = @[book, book1, book2];
    
    stu.books = arr;
    //获取值
    NSNumber *max = [stu valueForKeyPath:@"books.@max.price"];
    NSNumber *min = [stu valueForKeyPath:@"books.@min.price"];
    NSNumber *average = [stu valueForKeyPath:@"books.@avg.price"];
    NSLog(@"max: %@", max);
    NSLog(@"min: %@", min);
    NSLog(@"avg: %@", average);
}


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

    @autoreleasepool {
        fun1();
        fun2();
        fun3();
        fun4();
        fun5();
        fun6();
        fun7();
        fun8();
        fun9();
    }
    return 0;
}