KVC笔记

利用KVC可以随意修改一个对象的属性或者成员变量(并且私有的也可以修改)

示例代码:

 示例一:

Person *p = [[Person alloc] init];

p.dog = [[Dog alloc] init];

// 输出结果都一样

p.dog.name = @"wangcai";

[p.dog setValue:@"laifu" forKey:@"name"];

[p.dog setValue:@"haha" forKey:@"name"];

[p.dog setValue:@"laifu" forKeyPath:@"name"];

[p.dog setValue:@"haha" forKeyPath:@"name"];

// 区别

// forKeyPath包含了forKey的功能, 以后使用forKeyPath

// forKeyPath中可以利用.运算符, 一层一层往下查找对象的属性

//        [p setValue:@"laifu" forKey:@"dog.name"];   // 错误:没有dog.name的key

[p setValue:@"haha" forKeyPath:@"dog.name"];

NSLog(@"%@", p.dog.name);

示例二:

Person *p = [[Person alloc] init];

p.dog = [[Dog alloc] init];

p.dog.bone = [[Bone alloc] init];

p.dog.bone.type = @"骨头";

[p setValue:@"肉" forKeyPath:@"dog.bone.type"];

[p.dog setValue:@"肉" forKeyPath:@"bone.type"];

[p.dog.bone setValue:@"肉" forKeyPath:@"type"];

示例三: 用于获取值

Book *b1 = [[Book alloc] init];

b1.name = @"iOS";

b1.price = 10.5;

NSLog(@"%@", [b1 valueForKeyPath:@"name"]);

示例四:其他用法

Person *p = [[Person alloc] init];

Book *b1 = [[Book alloc] init];

b1.name = @"iOS";

b1.price = 10.5;

Book *b2 = [[Book alloc] init];

b2.name = @"Android";

b2.price = 15.5;

Book *b3 = [[Book alloc] init];

b3.name = @"PHP";

b3.price = 12.5;

Book *b4 = [[Book alloc] init];

b4.name = @"前端";

b4.price = 8;

p.books = @[b1, b2, b3, b4];

// 取出books数组中每一个元素的name属性值, 放到一个新的数组中返回

NSArray *names = [p valueForKeyPath:@"books.name"];

NSLog(@"%@", names);

// 利用KVC求和

double sum = [[p valueForKeyPath:@"books.@sum.price"] doubleValue];

// 利用KVC求平均

double average = [[p valueForKeyPath:@"books.@avg.price"] doubleValue];