如何观察 [NSCursor currentCursor] 的变化？

NSLog(@"当前鼠标光标：%@", [NSCursor currentCursor]);

@interface CursorObserver : NSObject

@property (nonatomic, strong) NSCursor *currentCursor;

@end

CursorObserver *cursorObserver = [[CursorObserver alloc] init];
[cursorObserver addObserver:self forKeyPath:@"currentCursor" options:NSKeyValueObservingOptionNew context:nil];

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"currentCursor"]) {
        NSCursor *newCursor = change[NSKeyValueChangeNewKey];
        NSLog(@"当前鼠标光标变化：%@", newCursor);
    }
}

@protocol CursorDelegate <NSObject>

- (void)cursorDidChange:(NSCursor *)cursor;

@end

- (void)setCurrentCursor:(NSCursor *)currentCursor {
    _currentCursor = currentCursor;
    if ([_delegate respondsToSelector:@selector(cursorDidChange:)]) {
        [_delegate cursorDidChange:currentCursor];
    }
}

- (void)cursorDidChange:(NSCursor *)cursor {
    NSLog(@"当前鼠标光标变化：%@", cursor);
}