实现原理：

其实是自定义一个view，将view添加到UITabBar上面，也可以是一个按钮，设置背景图片，和label。

废话少说直接上代码

搞一个UITabBar的分类

#import <UIKit/UIKit.h>
@interface UITabBar (Extension)
- (void)showBadgeOnItmIndex:(int)index;
- (void)hideBadgeOnItemIndex:(int)index;
@end

#import "UITabBar+Extension.h"
#define TabbarItemNums 5.0
@implementation UITabBar (badge)
//显示红点
- (void)showBadgeOnItmIndex:(int)index{
 [self removeBadgeOnItemIndex:index];
 //新建小红点
 UIView *bview = [[UIView alloc]init];
 bview.tag = 888+index;
 bview.layer.cornerRadius = 5;
 bview.clipsToBounds = YES;
 bview.backgroundColor = [UIColor redColor];
 CGRect tabFram = self.frame;

 float percentX = (index+0.6)/TabbarItemNums;
 CGFloat x = ceilf(percentX*tabFram.size.width);
 CGFloat y = ceilf(0.1*tabFram.size.height);
 bview.frame = CGRectMake(x, y, 10, 10);
 [self addSubview:bview];
 [self bringSubviewToFront:bview];
}
//隐藏红点
-(void)hideBadgeOnItemIndex:(int)index{
 [self removeBadgeOnItemIndex:index];
}
//移除控件
- (void)removeBadgeOnItemIndex:(int)index{
 for (UIView*subView in self.subviews) {
  if (subView.tag == 888+index) {
   [subView removeFromSuperview];
  }
 }
}
@end

最后在子控制器调用就可以啦

[self.tabBarController.tabBar showBadgeOnItmIndex:4];

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