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：
1 //.h文件
2 #import <Foundation/Foundation.h>
3 @class Book;
4 @interface Student : NSObject
5
6 @property (nonatomic, assign) int age;
7
8 @property (nonatomic, copy) NSString* name;
9
10
11 @property (nonatomic, strong) Book* book;
12
13 @property (nonatomic, strong) NSArray* books;
14 @end
15
16 //.m文件
17
18 #import "Student.h"
19 #import "Book.h"
20 @implementation Student
21
22
23 - (NSString *) description
24 {
25 return [NSString stringWithFormat:@"%@ %d", _name, _age];
26 }
27 @end
Book类：
1 //.h文件 2 #import <Foundation/Foundation.h> 3 4 @interface Book : NSObject 5 6 7 @property (nonatomic, assign) int price; 8 @end 9 10 //.m文件 11 #import "Book.h" 12 13 @implementation Book 14 15 @end
主函数：
1 #import <Foundation/Foundation.h>
2 #import "Student.h"
3 #import "Book.h"
4
5
6 //1.设值 取值
7 void fun1()
8 {
9 NSLog(@"==============fun1==============");
10 Student *stu = [[Student alloc] init];
11
12 [stu setValue:@"hehe" forKey:@"name"];
13 [stu setValue:@10 forKey:@"age"];
14
15 NSLog(@"%@", stu);
16
17 NSLog(@"name : %@", [stu valueForKey:@"name"]);
18 }
19
20 //2.批量获取属性值
21 void fun2()
22 {
23 NSLog(@"==============fun2==============");
24 Student *stu = [[Student alloc] init];
25
26 [stu setValue:@"hehe" forKey:@"name"];
27 [stu setValue:@10 forKey:@"age"];
28
29 NSArray *arr = @[@"name", @"age"];
30
31 NSDictionary *dict = [stu dictionaryWithValuesForKeys:arr];
32
33 NSLog(@"%@", dict);
34 }
35
36 //3.批量设置属性值（通过字典批量赋值）
37 void fun3()
38 {
39 NSLog(@"==============fun3==============");
40 Student *stu = [[Student alloc] init];
41
42 NSDictionary *dict = @{@"age": @12, @"name" : @"悟空"};
43
44 [stu setValuesForKeysWithDictionary:dict];
45
46 NSLog(@"%@", stu);
47 }
48
49
50 //4.通过键路径(key path)访问（使用valueForKeyPath）
51 void fun4()
52 {
53 NSLog(@"==============fun4==============");
54 Student *stu = [[Student alloc] init];
55 Book *book = [[Book alloc] init];
56 stu.book = book;
57 //设置值
58 [stu setValue:@12 forKeyPath:@"book.price"];
59 //获取值
60 NSNumber *price = [stu valueForKeyPath:@"book.price"];
61
62 NSLog(@"price: %@", price);
63 }
64
65 //5.对数组进行整体操作
66 void fun5()
67 {
68 NSLog(@"==============fun5==============");
69 Student *stu = [[Student alloc] init];
70
71 Book *book = [[Book alloc] init];
72 book.price = 12;
73 Book *book1 = [[Book alloc] init];
74 book1.price = 10;
75 Book *book2 = [[Book alloc] init];
76 book2.price = 12;
77
78 NSArray *arr = @[book, book1, book2];
79
80 stu.books = arr;
81 //获取值
82 // NSArray *prices = [stu valueForKeyPath:@"books.price"];
83 NSArray *prices = [stu.books valueForKeyPath:@"price"];
84 NSLog(@"prices: %@", prices);
85 }
86
87 //6.键路径的运算符（数组元素求和）
88 void fun6()
89 {
90 NSLog(@"==============fun6==============");
91 Student *stu = [[Student alloc] init];
92
93 Book *book = [[Book alloc] init];
94 book.price = 12;
95 Book *book1 = [[Book alloc] init];
96 book1.price = 10;
97 Book *book2 = [[Book alloc] init];
98 book2.price = 12;
99
100 NSArray *arr = @[book, book1, book2];
101
102 stu.books = arr;
103 //获取值
104 NSNumber *sum = [stu valueForKeyPath:@"books.@sum.price"];
105 NSLog(@"prices: %@", sum);
106 }
107
108 //7.键路径的运算符（数组总数count）
109 void fun7()
110 {
111 NSLog(@"==============fun7==============");
112 Student *stu = [[Student alloc] init];
113
114 Book *book = [[Book alloc] init];
115 book.price = 12;
116 Book *book1 = [[Book alloc] init];
117 book1.price = 10;
118 Book *book2 = [[Book alloc] init];
119 book2.price = 12;
120
121 NSArray *arr = @[book, book1, book2];
122
123 stu.books = arr;
124 //获取值
125 NSNumber *sum = [stu valueForKeyPath:@"books.@count.price"];
126 NSLog(@"num: %@", sum);
127 }
128
129 //8.键路径的运算符（获取数组不同元素）
130 void fun8()
131 {
132 NSLog(@"==============fun8==============");
133 Student *stu = [[Student alloc] init];
134
135 Book *book = [[Book alloc] init];
136 book.price = 12;
137 Book *book1 = [[Book alloc] init];
138 book1.price = 10;
139 Book *book2 = [[Book alloc] init];
140 book2.price = 12;
141
142 NSArray *arr = @[book, book1, book2];
143
144 stu.books = arr;
145 //获取值
146 NSArray *array = [stu valueForKeyPath:@"books.@distinctUnionOfObjects.price"];
147 NSLog(@"array: %@", array);
148 }
149
150 //9.求数组元素中得最大值、最小值、平均值
151 void fun9()
152 {
153 NSLog(@"==============fun9==============");
154 Student *stu = [[Student alloc] init];
155
156 Book *book = [[Book alloc] init];
157 book.price = 12;
158 Book *book1 = [[Book alloc] init];
159 book1.price = 10;
160 Book *book2 = [[Book alloc] init];
161 book2.price = 12;
162
163 NSArray *arr = @[book, book1, book2];
164
165 stu.books = arr;
166 //获取值
167 NSNumber *max = [stu valueForKeyPath:@"books.@max.price"];
168 NSNumber *min = [stu valueForKeyPath:@"books.@min.price"];
169 NSNumber *average = [stu valueForKeyPath:@"books.@avg.price"];
170 NSLog(@"max: %@", max);
171 NSLog(@"min: %@", min);
172 NSLog(@"avg: %@", average);
173 }
174
175
176 int main(int argc, const char * argv[])
177 {
178
179 @autoreleasepool {
180 fun1();
181 fun2();
182 fun3();
183 fun4();
184 fun5();
185 fun6();
186 fun7();
187 fun8();
188 fun9();
189 }
190 return 0;
191 }
转载于:https://www.cnblogs.com/pretty-guy/p/4056016.html