代码实现（在UITabBarViewController设置）：

- (void)setUpTabBar

{

    LHLTabBar *tabBar = [[LHLTabBar alloc] init];

    // 利用KVC对系统的tabBar进行赋值: KVC的原理是通过访问属性进行赋值,不是通过setter方法进行赋值

    [self setValue:tabBar forKeyPath:@"tabBar"];

}

底部UITabBar

#import <UIKit/UIKit.h>

@interface LHLTabBar : UITabBar

@end

#import "LHLTabBar.h"

@interface LHLTabBar ()

@property (nonatomic, weak) UIButton *plusButton;

@end

@implementation LHLTabBar

- (UIButton *)plusButton{

    if (_plusButton == nil) {

        UIButton *plusButton = [UIButton buttonWithType:UIButtonTypeCustom];

        [plusButton setBackgroundImage:[UIImage imageNamed:@"tabBar_publish_icon"] forState:UIControlStateNormal];

        [plusButton setBackgroundImage:[UIImage imageNamed:@"tabBar_publish_click_icon"] forState:UIControlStateHighlighted];

        [plusButton sizeToFit];

        [self addSubview:plusButton];

        _plusButton = plusButton;

    }

    return _plusButton;

}

- (void)layoutSubviews

{

    [super layoutSubviews];

    // 布局子控件

    NSInteger count = self.items.count + ;

    CGFloat btnW = self.lhl_width / count;

    CGFloat btnH = self.lhl_height;

    NSInteger i = ;

    for (UIButton *tabBarButton in self.subviews) {

        // 取出UITabBarButton

        if ([tabBarButton isKindOfClass:NSClassFromString(@"UITabBarButton")]) {

            if (i == ) {

                i += ;

            }

            tabBarButton.frame = CGRectMake(btnW * i, , btnW, btnH);

            i++;

        }

        // 隐藏tabBar黑线

        NSString *subFrames =  NSStringFromCGRect(tabBarButton.frame);

        NSString *blackLine = @"{{0, -0.5}, {375, 0.5}}";

        if ([subFrames isEqualToString:blackLine]) {

            tabBarButton.hidden = YES;

        }

    }

    // plusButton

    self.plusButton.center = CGPointMake(self.lhl_width * 0.5, self.frame.size.height * 0.5);

}

@end