OLKVO-KVC

参照： KVC & KVO 来源一: 很基础的一篇 KVO入门 来源二:
KVO进阶 来源三: 这篇比较深入，考虑也很周全
来源四:

KVO的常见错误

• 1.remove观察者

*** Terminating app due to uncaught exception 'NSRangeException', reason: 'Cannot remove an observer <SubViewController 0x7ff158707f80> for the key path "age" from <SubViewController 0x7ff158707f80> because it is not registered as an observer.'

修改前代码

// 添加观察者
    Person *person = [[Person alloc] init];
    person.name = @"hello";
    person.age = 23;
    self.subPersonKVO = person;
    [self.subPersonKVO addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:@"SubViewController"];

// 移除观察者 在dealloc中
    [self removeObserver:self forKeyPath:@"age" context:@"SubViewController"];

============= 解决方案

// 移除观察者 在dealloc中
    [self.subPersonKVO removeObserver:self forKeyPath:@"age" context:@"SubViewController"];

self -> self.subPersonKVO 关键点就在这里，观察谁，谁就应该移除

• 2.值修改了，但是并没有接收到

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '<SubViewController: 0x7fc273d13450>: An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
Key path: age

解决方案：添加该方法

`- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
    NSLog(@"keyPath=%@", keyPath);
    self.subLabelKVO.text = [NSString stringWithFormat:@"%@现在的年龄是: %zd", self.subPersonKVO.name, self.subPersonKVO.age];
}

• 3.context上下文不一致，也可以理解为标识符不统一

*** Terminating app due to uncaught exception 'NSRangeException', reason: 'Cannot remove an observer <SubViewController 0x7fc175001d60> for the key path "age" from <Person 0x7fc172da5be0> because it is not registered as an observer.'

修改前

`- (void) kvo {
Person *person = [[Person alloc] init];
    person.name = @"hello";
    person.age = 23;
    self.subPersonKVO = person;
    [self.subPersonKVO addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:@"SubViewController"];
}
`- (void)dealloc {
    [self.subPersonKVO removeObserver:self forKeyPath:@"age" context:nil];
}

====== 解决方案：context 统一

`- (void)dealloc {
    [self.subPersonKVO removeObserver:self forKeyPath:@"age" context:@"SubViewController"];
}

一般来说context都是nil,但是个人还是觉得区别开来为好