先上图：
如果我们要实现中间按钮自定义样式，方法应该蛮多，这里介绍一种最简单的。
1、创建类继承：UITabBarController，如下代码都是写在该类的 .m文件里
2、定义最中间的自定义样式，写在viewDidLoad里
UIButton *btn = [[UIButton alloc] init];
btn.layer.cornerRadius = 30;
btn.layer.masksToBounds = YES;
btn.backgroundColor = [UIColor redColor];
btn.frame = CGRectMake(0, 0, 60, 60);
CGPoint center = self.tabBar.center;
center.y=center.y-15;
btn.center = center;
[self.view addSubview:btn];
[btn addTarget:self action:@selector(hhhCLick) forControlEvents:UIControlEventTouchUpInside];
这里解释一下：
我们获取当前tabbar的center点，然后自定义一个按钮，给予自己想要的样式，然后add上去。
这里要注意一点，这里用的自定义按钮，没有用系统tabbarItem，所以最后setViewController的时候要留出位置。
完整代码如下：
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
HomeViewController *home = [[HomeViewController alloc] init];
UINavigationController *homeNav = [[UINavigationController alloc] initWithRootViewController:home];
home.title = @"相册";
home.navigationItem.title = @"相册";
home.tabBarItem.image = [[UIImage imageNamed:@"home"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
home.tabBarItem.selectedImage = [[UIImage imageNamed:@"home_selected"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
VideoViewController *pic = [[VideoViewController alloc] init];
UINavigationController *picNav = [[UINavigationController alloc] initWithRootViewController:pic];
pic.title = @"视频";
pic.navigationItem.title = @"视频";
pic.tabBarItem.image = [[UIImage imageNamed:@"picture"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
pic.tabBarItem.selectedImage = [[UIImage imageNamed:@"picture_selected"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
SeetingViewController *setting = [[SeetingViewController alloc] init];
UINavigationController *setNav = [[UINavigationController alloc] initWithRootViewController:setting];
setting.tabBarItem.title = @"设置";
setting.navigationItem.title = @"设置";
setting.tabBarItem.image = [[UIImage imageNamed:@"setting"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
setting.tabBarItem.selectedImage = [[UIImage imageNamed:@"setting_selected"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
SeetingViewController *setting222 = [[SeetingViewController alloc] init];
UINavigationController *setNav222 = [[UINavigationController alloc] initWithRootViewController:setting222];
setting222.tabBarItem.title = @"设置2";
setting222.navigationItem.title = @"设置2";
setting222.tabBarItem.image = [[UIImage imageNamed:@"setting"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
setting222.tabBarItem.selectedImage = [[UIImage imageNamed:@"setting_selected"] imageWithRenderingMode:UIImageRenderingModeAutomatic];
NSMutableArray *arry = [[NSMutableArray alloc] init];
[arry addObject:homeNav];
[arry addObject:picNav];
[arry addObject:[UIViewController new]];
[arry addObject:setNav222];
[arry addObject:setNav];
[self setViewControllers:arry animated:YES];
//－－－－－－－－－－－这里是自定义样式按钮－－－－－－－－－－－
UIButton *btn = [[UIButton alloc] init];
btn.layer.cornerRadius = 30;
btn.layer.masksToBounds = YES;
btn.backgroundColor = [UIColor redColor];
btn.frame = CGRectMake(0, 0, 60, 60);
CGPoint center = self.tabBar.center;
center.y=center.y-15;
btn.center = center;
[self.view addSubview:btn];
[btn addTarget:self action:@selector(hhhCLick) forControlEvents:UIControlEventTouchUpInside];
}
点击按钮事件，自己可以Modal到新控制器。
-(void)hhhCLick{
SeetingViewController *setting111 = [[SeetingViewController alloc] init];
UINavigationController *setNav111 = [[UINavigationController alloc] initWithRootViewController:setting111];
setting111.tabBarItem.title = @"";
setting111.navigationItem.title = @"设置1";
[self presentViewController:setNav111 animated:YES completion:nil];
}