a) KVO的全称是Key-Value-Observing,俗称"键值监听"，可以用于监听某个对象属性值的改变
a) 调用willChangeValueForKey:
b) 调用原来的setter实现
c) 调用didChangeValueForKey:
didChangeValueForKey:内部会调用observer的observeValueForKeyPath:ofObject:change:context:方法
6.iOS用什么方式实现对一个对象的KVO？(KVO的本质是什么？)
a) 利用RuntimeAPI动态生成一个子类NSKVONotifying_类名继承自类名的类，并且让instance对象的isa指向这个全新的子类
b) 当修改instance对象的属性时，会调用Foundation的_NSSetXXXValueAndNotify函数
1) willChangeValueForKey:
2) 父类原来的setter
3) didChangeValueForKey:
3.1) 内部会触发监听器（Oberser）的监听方法(observeValueForKeyPath:ofObject:change:context:）
a) 手动调用willChangeValueForKey:和didChangeValueForKey:
a) 不会触发KVO 解读KVO的本质即可即实则修改了属性setter方法的实现
a) 肯定是代理的效率高，不需要动态生成一些方法直接拿到代理调用对应的方法即可
10.如何验证确实执行的是_NSSet*AndNotify函数？
@interface ViewController ()
@property (strong, nonatomic) MJPerson *person1;
@property (strong, nonatomic) MJPerson *person2;
@end
// 反编译工具 - Hopper
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.person1 = [[MJPerson alloc] init];
self.person1.age = 1;
self.person2 = [[MJPerson alloc] init];
self.person2.age = 2;
// NSLog(@"person1添加KVO监听之前 - %@ %@",
// object_getClass(self.person1),
// object_getClass(self.person2));
// NSLog(@"person1添加KVO监听之前 - %p %p",
// [self.person1 methodForSelector:@selector(setAge:)],
// [self.person2 methodForSelector:@selector(setAge:)]);
// 给person1对象添加KVO监听
NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
[self.person1 addObserver:self forKeyPath:@"age" options:options context:@"123"];
// NSLog(@"person1添加KVO监听之后 - %@ %@",
// object_getClass(self.person1),
// object_getClass(self.person2));
// NSLog(@"person1添加KVO监听之后 - %p %p",
// [self.person1 methodForSelector:@selector(setAge:)],
// [self.person2 methodForSelector:@selector(setAge:)]);
//
//
// NSLog(@"类对象 - %@ %@",
// object_getClass(self.person1), // self.person1.isa
// object_getClass(self.person2)); // self.person2.isa
//
// NSLog(@"元类对象 - %@ %@",
// object_getClass(object_getClass(self.person1)), // self.person1.isa.isa
// object_getClass(object_getClass(self.person2))); // self.person2.isa.isa
}
11.如何验证NSKVONotifying_类名其他的方法？
@interface ViewController ()
@property (strong, nonatomic) MJPerson *person1;
@property (strong, nonatomic) MJPerson *person2;
@end
//@implementation NSObject
//
//- (Class)class
//{
// return object_getClass(self);
//}
//
//@end
// 反编译工具 - Hopper
@implementation ViewController
- (void)printMethodNamesOfClass:(Class)cls
{
unsigned int count;
// 获得方法数组
Method *methodList = class_copyMethodList(cls, &count);
// 存储方法名
NSMutableString *methodNames = [NSMutableString string];
// 遍历所有的方法
for (int i = 0; i < count; i++) {
// 获得方法
Method method = methodList[I];
// 获得方法名
NSString *methodName = NSStringFromSelector(method_getName(method));
// 拼接方法名
[methodNames appendString:methodName];
[methodNames appendString:@", "];
}
// 释放
free(methodList);
// 打印方法名
NSLog(@"%@ %@", cls, methodNames);
}
- (void)viewDidLoad {
[super viewDidLoad];
self.person1 = [[MJPerson alloc] init];
self.person1.age = 1;
self.person2 = [[MJPerson alloc] init];
self.person2.age = 2;
// 给person1对象添加KVO监听
NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
[self.person1 addObserver:self forKeyPath:@"age" options:options context:@"123"];
[self printMethodNamesOfClass:object_getClass(self.person1)];
[self printMethodNamesOfClass:object_getClass(self.person2)];
}
