1、需要两个类：
（1）TBTabBar

#import <UIKit/UIKit.h>

@interface TBTabBar : UITabBar

//@property(nonatomic,strong)UIButton *publishBtn;

@property (nonatomic,copy) void(^didClickPublishBtn)();

@end

#import "TBTabBar.h"
//button拓展类
#import "UIButton+SSEdgeInsets.h"

@interface TBTabBar ()

/** plus按钮 */
@property (nonatomic, weak) UIButton *plusBtn ;

@end

@implementation TBTabBar

- (void)layoutSubviews {
    [super layoutSubviews];
    
    CGFloat w = self.width/5.0;
    
    UIButton *publishBtn = [[UIButton alloc] init];
    [publishBtn setImage:[UIImage imageNamed:@"发布3.3"] forState:UIControlStateNormal];
    [publishBtn setTitle:@"  " forState:UIControlStateNormal];
    publishBtn.titleLabel.font = [UIFont systemFontOfSize:10];
    [publishBtn addTarget:self action:@selector(didClickPublishBtn:) forControlEvents:UIControlEventTouchUpInside];
    publishBtn.adjustsImageWhenHighlighted = NO;
    publishBtn.size = CGSizeMake(w, 70);
    publishBtn.centerX = self.width / 2;
    publishBtn.centerY = 12;
    [publishBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [self addSubview:publishBtn];
    self.plusBtn = publishBtn;
    //button按钮
    [publishBtn setImagePositionWithType:SSImagePositionTypeTop spacing:5];
    
    
    // 其他位置按钮
    NSUInteger count = self.subviews.count;
    for (NSUInteger i = 0 , j = 0; i < count; i++) {
        UIView *view = self.subviews[i];
        Class class = NSClassFromString(@"UITabBarButton");
        if ([view isKindOfClass:class]) {
            view.width = self.width / 5.0;
            view.x = self.width * j / 5.0;
            
            j++;
            if (j == 2) {
                j++;
            }
        }
    }
    
}

// 点击发布
- (void) didClickPublishBtn:(UIButton*)sender {
    //    NSLog(@"点击了发布");
    if (self.didClickPublishBtn) {
        self.didClickPublishBtn();
    }
}

//重写hitTest方法，去监听发布按钮的点击，目的是为了让凸出的部分点击也有反应
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
    
    //这一个判断是关键，不判断的话push到其他页面，点击发布按钮的位置也是会有反应的，这样就不好了
    //self.isHidden == NO 说明当前页面是有tabbar的，那么肯定是在导航控制器的根控制器页面
    //在导航控制器根控制器页面，那么我们就需要判断手指点击的位置是否在发布按钮身上
    //是的话让发布按钮自己处理点击事件，不是的话让系统去处理点击事件就可以了
    if (self.isHidden == NO) {
        
        //将当前tabbar的触摸点转换坐标系，转换到发布按钮的身上，生成一个新的点
        CGPoint newP = [self convertPoint:point toView:self.plusBtn];
        
        //判断如果这个新的点是在发布按钮身上，那么处理点击事件最合适的view就是发布按钮
        if ( [self.plusBtn pointInside:newP withEvent:event]) {
            return self.plusBtn;
        }else{//如果点不在发布按钮身上，直接让系统处理就可以了
            
            return [super hitTest:point withEvent:event];
        }
    }
    
    else {//tabbar隐藏了，那么说明已经push到其他的页面了，这个时候还是让系统去判断最合适的view处理就好了
        
        return [super hitTest:point withEvent:event];
    }
}

@end

（2）UIButton+SSEdgeInsets

#import <UIKit/UIKit.h>

typedef NS_ENUM(NSInteger, SSImagePositionType) {
    SSImagePositionTypeLeft,   //图片在左，标题在右，默认风格
    SSImagePositionTypeRight,  //图片在右，标题在左
    SSImagePositionTypeTop,    //图片在上，标题在下
    SSImagePositionTypeBottom  //图片在下，标题在上
};

typedef NS_ENUM(NSInteger, SSEdgeInsetsType) {
    SSEdgeInsetsTypeTitle,//标题
    SSEdgeInsetsTypeImage//图片
};

typedef NS_ENUM(NSInteger, SSMarginType) {
    SSMarginTypeTop         ,
    SSMarginTypeBottom      ,
    SSMarginTypeLeft        ,
    SSMarginTypeRight       ,
    SSMarginTypeTopLeft     ,
    SSMarginTypeTopRight    ,
    SSMarginTypeBottomLeft  ,
    SSMarginTypeBottomRight
};

/**
 默认情况下，imageEdgeInsets和titleEdgeInsets都是0。先不考虑height,
 
 if (button.width小于imageView上image的width){图像会被压缩，文字不显示}
 
 if (button.width < imageView.width + label.width){图像正常显示，文字显示不全}
 
 if (button.width >＝ imageView.width + label.width){图像和文字都居中显示，imageView在左，label在右，中间没有空隙}
 */

@interface UIButton (SSEdgeInsets)

/**
 *  利用UIButton的titleEdgeInsets和imageEdgeInsets来实现图片和标题的自由排布
 *  注意：1.该方法需在设置图片和标题之后才调用;
         2.图片和标题改变后需再次调用以重新计算titleEdgeInsets和imageEdgeInsets
 *
 *  @param type    图片位置类型
 *  @param spacing 图片和标题之间的间隙
 */
- (void)setImagePositionWithType:(SSImagePositionType)type spacing:(CGFloat)spacing;

/**
 *  按钮只设置了title or image，该方法可以改变它们的位置
 *
 *  @param edgeInsetsType <#edgeInsetsType description#>
 *  @param marginType     <#marginType description#>
 *  @param margin         <#margin description#>
 */
- (void)setEdgeInsetsWithType:(SSEdgeInsetsType)edgeInsetsType marginType:(SSMarginType)marginType margin:(CGFloat)margin;



/**
 *  图片在上，标题在下
 *
 *  @param spacing image 和 title 之间的间隙
 */
- (void)setImageUpTitleDownWithSpacing:(CGFloat)spacing __deprecated_msg("Method deprecated. Use `setImagePositionWithType:spacing:`");

/**
 *  图片在右，标题在左
 *
 *  @param spacing image 和 title 之间的间隙
 */
- (void)setImageRightTitleLeftWithSpacing:(CGFloat)spacing __deprecated_msg("Method deprecated. Use `setImagePositionWithType:spacing:`");

@end

#import "UIButton+SSEdgeInsets.h"

#if __IPHONE_OS_VERSION_MIN_REQUIRED >= 70000
#define SS_SINGLELINE_TEXTSIZE(text, font) [text length] > 0 ? [text \
sizeWithAttributes:@{NSFontAttributeName:font}] : CGSizeZero;
#else
#define SS_SINGLELINE_TEXTSIZE(text, font) [text length] > 0 ? [text sizeWithFont:font] : CGSizeZero;
#endif

@implementation UIButton (SSEdgeInsets)

- (void)setImagePositionWithType:(SSImagePositionType)type spacing:(CGFloat)spacing {
    CGSize imageSize = [self imageForState:UIControlStateNormal].size;
    CGSize titleSize = SS_SINGLELINE_TEXTSIZE([self titleForState:UIControlStateNormal], self.titleLabel.font);

    switch (type) {
        case SSImagePositionTypeLeft: {
            self.titleEdgeInsets = UIEdgeInsetsMake(0, spacing, 0, 0);
            self.imageEdgeInsets = UIEdgeInsetsMake(0, 0, 0, spacing);
            break;
        }
        case SSImagePositionTypeRight: {
            self.titleEdgeInsets = UIEdgeInsetsMake(0, - imageSize.width, 0, imageSize.width + spacing);
            self.imageEdgeInsets = UIEdgeInsetsMake(0, titleSize.width + spacing, 0, - titleSize.width);
            break;
        }
        case SSImagePositionTypeTop: {
            // lower the text and push it left so it appears centered
            //  below the image
            self.titleEdgeInsets = UIEdgeInsetsMake(0, - imageSize.width, - (imageSize.height + spacing), 0);
            
            // raise the image and push it right so it appears centered
            //  above the text
            self.imageEdgeInsets = UIEdgeInsetsMake(- (titleSize.height + spacing), 0, 0, - titleSize.width);
            break;
        }
        case SSImagePositionTypeBottom: {
            self.titleEdgeInsets = UIEdgeInsetsMake(- (imageSize.height + spacing), - imageSize.width, 0, 0);
            self.imageEdgeInsets = UIEdgeInsetsMake(0, 0, - (titleSize.height + spacing), - titleSize.width);
            break;
        }
    }
}

- (void)setImageUpTitleDownWithSpacing:(CGFloat)spacing {
    [self setImagePositionWithType:SSImagePositionTypeTop spacing:spacing];
}

- (void)setImageRightTitleLeftWithSpacing:(CGFloat)spacing {
    [self setImagePositionWithType:SSImagePositionTypeRight spacing:spacing];
}

- (void)setEdgeInsetsWithType:(SSEdgeInsetsType)edgeInsetsType marginType:(SSMarginType)marginType margin:(CGFloat)margin {
    CGSize itemSize = CGSizeZero;
    if (edgeInsetsType == SSEdgeInsetsTypeTitle) {
        itemSize = SS_SINGLELINE_TEXTSIZE([self titleForState:UIControlStateNormal], self.titleLabel.font);
    } else {
        itemSize = [self imageForState:UIControlStateNormal].size;
    }
    
    CGFloat horizontalDelta = (CGRectGetWidth(self.frame) - itemSize.width) / 2.f - margin;
    CGFloat vertivalDelta = (CGRectGetHeight(self.frame) - itemSize.height) / 2.f - margin;
    
    NSInteger horizontalSignFlag = 1;
    NSInteger verticalSignFlag = 1;
    
    switch (marginType) {
        case SSMarginTypeTop: {
            horizontalSignFlag = 0;
            verticalSignFlag = - 1;
            break;
        }
        case SSMarginTypeBottom: {
            horizontalSignFlag = 0;
            verticalSignFlag = 1;
            break;
        }
        case SSMarginTypeLeft: {
            horizontalSignFlag = - 1;
            verticalSignFlag = 0;
            break;
        }
        case SSMarginTypeRight: {
            horizontalSignFlag = 1;
            verticalSignFlag = 0;
            break;
        }
        case SSMarginTypeTopLeft: {
            horizontalSignFlag = - 1;
            verticalSignFlag = - 1;
            break;
        }
        case SSMarginTypeTopRight: {
            horizontalSignFlag = 1;
            verticalSignFlag = - 1;
            break;
        }
        case SSMarginTypeBottomLeft: {
            horizontalSignFlag = - 1;
            verticalSignFlag = 1;
            break;
        }
        case SSMarginTypeBottomRight: {
            horizontalSignFlag = 1;
            verticalSignFlag = 1;
            break;
        }
    }
    
    UIEdgeInsets edgeInsets = UIEdgeInsetsMake(vertivalDelta * verticalSignFlag, horizontalDelta * horizontalSignFlag, - vertivalDelta * verticalSignFlag, - horizontalDelta * horizontalSignFlag);
    if (edgeInsetsType == SSEdgeInsetsTypeTitle) {
        self.titleEdgeInsets = edgeInsets;
    } else {
        self.imageEdgeInsets = edgeInsets;
    }
}

@end

2、控制器里：MainViewController

#import <UIKit/UIKit.h>

@interface MainViewController : UITabBarController

@end

#import "MainViewController.h"
//tabbar
#import "TBTabBar.h"
//导航栏
#import "MineNavigationController.h"
//主页
#import "MainHomeViewControllerV3_3.h"
//逛街
#import "ShoppingViewController.h"
//美聊
#import "BeautyChatControllerV2_0.h"
//个人中心3.1.0
#import "MyCenterViewController3_1_0.h"
//发布话题
#import "SendTopicViewController.h"

@interface MainViewController ()
/** 之前被选中的UITabBarItem */
@property (nonatomic, strong) UITabBarItem *lastItem;

@end

@implementation MainViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 初始化所有控制器
    [self setUpChildVC];
    
    // 创建tabbar中间的tabbarItem
    [self setUpMidelTabbarItem];
    
}

#pragma mark -创建tabbar中间的tabbarItem

- (void)setUpMidelTabbarItem {
    
    TBTabBar *tabBar = [[TBTabBar alloc] init];
     // KVC：如果要修系统的某些属性，但被设为readOnly，就是用KVC，即setValue：forKey：。
    [self setValue:tabBar forKey:@"tabBar"];
    
    //去掉黑线,然后替换tabbar上面那一条线,下面两个方法必须同时设置，否则无效imageWithColor是根据颜色生成图片的封装
    [tabBar setBackgroundImage:[UIImage imageWithColor:[UIColor whiteColor] size:CGSizeMake(self.view.frame.size.width, .5)]];
    [tabBar setShadowImage:[UIImage imageWithColor:[UIColor colorWithHexString:@"#d1d3db"] size:CGSizeMake(self.view.frame.size.width, .5)]];
    
    
    //（3）设置其他属性
    tabBar.barTintColor = [UIColor whiteColor];//设置tabbar背景颜色
    tabBar.translucent = NO;
   
    
    // 二次点击触发刷新将默认被选中的tabBarItem保存为属性
    self.lastItem = tabBar.selectedItem;
    

    
    //中间发布按钮点击回调
    __weak typeof(self) weakSelf = self;
    [tabBar setDidClickPublishBtn:^{
        
        //凸出按钮点击事件
        [weakSelf plusBtnClick];
        
    }];
    
}

#pragma mark -初始化所有控制器

- (void)setUpChildVC {
    
    MainHomeViewControllerV3_3 *homeVC = [[MainHomeViewControllerV3_3 alloc] init];
    //设置角标数量
//    homeVC.tabBarItem.badgeValue = @"1111";
    [self setChildVC:homeVC title:@"" image:@"首页" selectedImage:@"首页s"];
    
    ShoppingViewController *fishpidVC = [[ShoppingViewController alloc] init];
    [self setChildVC:fishpidVC title:@"" image:@"逛街" selectedImage:@"逛街s"];
    
    BeautyChatControllerV2_0 *messageVC = [[BeautyChatControllerV2_0 alloc] init];
    [self setChildVC:messageVC title:@"" image:@"美聊"  selectedImage:@"美聊s"];
    
    MyCenterViewController3_1_0 *myVC = [[MyCenterViewController3_1_0 alloc] init];
    [self setChildVC:myVC title:@"" image:@"我的" selectedImage:@"我的s"];
    
  
    
}

//设置子控制器
- (void) setChildVC:(UIViewController *)childVC title:(NSString *) title image:(NSString *) image selectedImage:(NSString *) selectedImage {
    
    childVC.tabBarItem.title = title;
    //设置字体属性
    NSMutableDictionary *dict = [NSMutableDictionary dictionary];
    dict[NSForegroundColorAttributeName] = [UIColor blackColor];
    dict[NSFontAttributeName] = [UIFont systemFontOfSize:10];
    
    // 禁用图片渲染
    [childVC.tabBarItem setTitleTextAttributes:dict forState:UIControlStateNormal];
    childVC.tabBarItem.image = [[UIImage imageNamed:image] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
    childVC.tabBarItem.selectedImage = [[UIImage imageNamed:selectedImage] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];

    //字控制器图片调整位置
    childVC.tabBarItem.imageInsets =  UIEdgeInsetsMake(5, 0, -5, 0);
    
    //    childVc.view.backgroundColor = RandomColor; // 这句代码会自动加载主页，消息，发现，我四个控制器的view，但是view要在我们用的时候去提前加载
    
    //导航
    MineNavigationController *nav = [[MineNavigationController alloc] initWithRootViewController:childVC];
    //导航栏颜色
    nav.navigationBar.barTintColor = [UIColor whiteColor];
    
    [self addChildViewController:nav];
}

//二次点击tabbar触发刷新代理方法
- (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item
{
    // 判断本次点击的UITabBarItem是否和上次的一样
    if (item == self.lastItem) { // 一样就发出通知
        [[NSNotificationCenter defaultCenter] postNotificationName:@"LLTabBarDidClickNotification" object:nil userInfo:nil];
    }
    // 将这次点击的UITabBarItem赋值给属性
    self.lastItem = item;
    
}



//发布按钮
- (void)plusBtnClick{
    
    //友盟点击量统计
    [MobClick event:@"changwenfabu"];
    //push控制器
    MineNavigationController * nav = [(UITabBarController *)[UIApplication sharedApplication].keyWindow.rootViewController selectedViewController];
    
    if (SESSIONID.length>0) {
        //跳转到发话题界面
        SendTopicViewController * SendTopic = [[SendTopicViewController alloc]init];
        SendTopic.hidesBottomBarWhenPushed = YES;
        SendTopic.type = @"UGC话题";
        [nav pushViewController:SendTopic animated:YES];
        
    }else{
        //跳到登陆界面
        LoginViewController * loginVc = [[LoginViewController alloc]init];
        loginVc.hidesBottomBarWhenPushed = YES;
        [nav pushViewController:loginVc animated:YES];
        
    }

    
  
}


#pragma mark ====================== 处理屏幕旋转（在用，请不要删）=========================
-(BOOL)shouldAutorotate{
   return [self.selectedViewController shouldAutorotate];
}
- (UIInterfaceOrientationMask)supportedInterfaceOrientations
{
    return [self.selectedViewController supportedInterfaceOrientations];
}
- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation {
    return [self.selectedViewController preferredInterfaceOrientationForPresentation];
}


@end

总结：这是我用过最好的中间凸出的tabbar了，希望大家喜欢（2017年6月13日）