如何在UITabBarItem中添加小红点

// Swift 示例
tabBarController?.tabBar.items?[0].badgeValue = "99+"

// Objective-C 示例
tabBarController.tabBar.items[0].badgeValue = @"99+";

// Swift 示例
if let tabBarItem = tabBarController?.tabBar.items?[0] {
    let customView = UIView(frame: CGRect(x: 0, y: 0, width: 8, height: 8))
    customView.backgroundColor = .red
    customView.layer.cornerRadius = customView.frame.size.width / 2
    customView.clipsToBounds = true
    tabBarItem.setValue(customView, forKey: "_customView")
}

// Objective-C 示例
UITabBarItem *tabBarItem = [tabBarController.tabBar.items objectAtIndex:0];
UIView *customView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 8, 8)];
customView.backgroundColor = [UIColor redColor];
customView.layer.cornerRadius = customView.frame.size.width / 2;
customView.clipsToBounds = YES;
[tabBarItem setValue:customView forKey:@"_customView"];