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:@ 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:@ 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": @, @"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:@ 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 = ;
     Book *book1 = [[Book alloc] init];
     book1.price = ;
     Book *book2 = [[Book alloc] init];
     book2.price = ;

     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 = ;
     Book *book1 = [[Book alloc] init];
     book1.price = ;
     Book *book2 = [[Book alloc] init];
     book2.price = ;

     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 = ;
     Book *book1 = [[Book alloc] init];
     book1.price = ;
     Book *book2 = [[Book alloc] init];
     book2.price = ;

     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 = ;
     Book *book1 = [[Book alloc] init];
     book1.price = ;
     Book *book2 = [[Book alloc] init];
     book2.price = ;

     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 = ;
     Book *book1 = [[Book alloc] init];
     book1.price = ;
     Book *book2 = [[Book alloc] init];
     book2.price = ;

     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 ;
 }