在我们的项目经常会遇到这样的需求：当有新消息出现的时候，需要显示一个小红点提醒用户有新消息了。效果如图：

下面是代码：

为UITabBar写一个Category
.h中：
#import <UIKit/UIKit.h>

@interface UITabBar (badge)
//显示小红点
- (void)showBadgeOnItemIndex:(int)index;
//隐藏小红点
- (void)hideBadgeOnItemIndex:(int)index;

@end

#import "UITabBar+badge.h"
#define TabbarItemNums 5.0    //tabbar的数量
@implementation UITabBar (badge)
- (void)showBadgeOnItemIndex:(int)index{
    
    //移除之前的小红点
    [self removeBadgeOnItemIndex:index];
    
    //新建小红点
    UIView *badgeView = [[UIView alloc]init];
    badgeView.tag = 888 + index;
    badgeView.layer.cornerRadius = 5;
    badgeView.backgroundColor = [UIColor redColor];
    CGRect tabFrame = self.frame;
    
    //确定小红点的位置
    float percentX = (index +0.6) / TabbarItemNums;
    CGFloat x = ceilf(percentX * tabFrame.size.width);
    CGFloat y = ceilf(0.1 * tabFrame.size.height);
    badgeView.frame = CGRectMake(x, y, 10, 10);
    [self addSubview:badgeView];
    
}

- (void)hideBadgeOnItemIndex:(int)index{
    
    //移除小红点
    [self removeBadgeOnItemIndex:index];
    
}

- (void)removeBadgeOnItemIndex:(int)index{
    
    //按照tag值进行移除
    for (UIView *subView in self.subviews) {
        
        if (subView.tag == 888+index) {
            
            [subView removeFromSuperview];
            
        }
    }
}
@end

在需要的地方调用：
如：
[tabBar showBadgeOnItemIndex:3];