如何在Objective C中的UINavigation栏上显示通知计数

#import <UIKit/UIKit.h>

UILabel *notificationLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 20, 20)];
notificationLabel.backgroundColor = [UIColor redColor];
notificationLabel.textColor = [UIColor whiteColor];
notificationLabel.textAlignment = NSTextAlignmentCenter;
notificationLabel.font = [UIFont systemFontOfSize:12];
notificationLabel.layer.cornerRadius = 10;
notificationLabel.layer.masksToBounds = YES;

UINavigationBar *navigationBar = self.navigationController.navigationBar;
[navigationBar addSubview:notificationLabel];

NSInteger notificationCount = 10; // 通知计数的值
notificationLabel.text = [NSString stringWithFormat:@"%ld", (long)notificationCount];

CGFloat labelX = navigationBar.frame.size.width - notificationLabel.frame.size.width - 10;
CGFloat labelY = (navigationBar.frame.size.height - notificationLabel.frame.size.height) / 2;
notificationLabel.frame = CGRectMake(labelX, labelY, notificationLabel.frame.size.width, notificationLabel.frame.size.height);