iOS TabBarItem设置红点（未读消息）

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 (badge)

- (void)showBadgeOnItemIndex:(int)index;
- (void)hideBadgeOnItemIndex:(int)index;

@end

#import "UITabBar+badge.h"

#define TabbarItemNums 5.0

@implementation UITabBar (badge)

// 显示红点
- (void)showBadgeOnItemIndex:(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

#import "UITabBar+badge.h"

 [self.tabBarController.tabBar showBadgeOnItemIndex:4];

swift版带消息个数

import UIKit

extension UITabBar {

    func showBadgeOnItem(index:Int, count:Int) {

        removeBadgeOnItem(index: index)
        let bview = UIView.init()
        bview.tag = 888+index
        bview.layer.cornerRadius = 9
        bview.clipsToBounds = true
        bview.backgroundColor = UIColor.red
        let tabFrame = self.frame
        
        let percentX = (Float(index)+0.6) / 5.0(tabBar的总个数)
        let x = CGFloat(ceilf(percentX*Float(tabFrame.width)))
        let y = CGFloat(ceilf(0.1*Float(tabFrame.height)))
        bview.frame = CGRect(x: x, y: y,  18, height: 18)
        
        let cLabel = UILabel.init()
        cLabel.text = "(count)"
        cLabel.frame = CGRect(x: 0, y: 0,  18, height: 18)
        cLabel.font = UIFont.systemFont(ofSize: 10)
        cLabel.textColor = UIColor.white
        cLabel.textAlignment = .center
        bview.addSubview(cLabel)
        
        addSubview(bview)
        bringSubview(toFront: bview)
    }
    // 隐藏红点
    func hideBadgeOnItem(index:Int) {

        removeBadgeOnItem(index: index)
    }
    // 移除控件
    func removeBadgeOnItem(index:Int) {

        for subView:UIView in subviews {
            if subView.tag == 888+index {
                subView.removeFromSuperview()
            }
        }
    }
}