1 // 第二步：实现回调
 2 - (void)observeva lueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
 3 {
 4     
 5     NSLog(@"keyPath = %@", keyPath);
 6     NSLog(@"object = %@", object);
 7     NSLog(@"change = %@", change);
 8     
 9     // 可以进行刷新UI的操作
10 }

 1 // 第二步：实现回调
 2 - (void)observeva lueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
 3 {
 4     
 5     NSLog(@"keyPath = %@", keyPath);
 6     NSLog(@"object = %@", object);
 7     NSLog(@"change = %@", change);
 8     
 9     // 可以进行刷新UI的操作
10 }

1 // 视图将要消失的时候
2 - (void)viewWillDisappear:(BOOL)animated
3 {
4     // 在不需要观察者的时候需要把它删除
5     [self removeObserver:self forKeyPath:@"array"];
6 }