iOS开发-4.KVO

• 1.什么是KVO？

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

• 2.未使用KVO监听的对象
  

• 3.使用了KVO监听的对象
  

• 4.查看_NSSet*AndNotify的存在
  

• 5._NSSet*ValueAndNotify的内部实现

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:）

• 7.如何手动触发KVO

a) 手动调用willChangeValueForKey:和didChangeValueForKey:

• 8.直接修改成员变量会触发KVO么？

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

• 9.KVO的效率高还是代理的效率高？

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)];
}