如何创建 TabBar上面创建一个与其他按钮不同的按钮，如中间按钮

如何创建一个中间为红色的按钮呢 ？比如如图的按钮。

因为 tabBar 是 readonly 只读属性，所以不能使用下方的创建方式来自定义tabbar.

@property(nonatomic,readonly) UITabBar *tabBar NS_AVAILABLE_IOS(3_0); // Provided for -[UIActionSheet showFromTabBar:]. Attempting to modify the contents of the tab bar directly will throw an exception.


    // 不能使用这句话进行 创建自定义tabBar,因为 tabBar 是 只读属性。
    self.tabBar = [[LTabBar alloc] init];

这个时候就可以使用KVC. 看下面的代码：

[self setValue:[[LTabBar alloc] init] forKeyPath:@"tabBar"];

LTabBar 是你创建的一个继承制 “UITabBar” 的类的类名。在 “LTabBar.m" 中写 下面的代码：

#import "LTabBar.h"

@interface LTabBar()
/** 发布按钮 */
@property (nonatomic, weak) UIButton *publishButton;
@end

@implementation LTabBar

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        
        UIButton *publishButton = [UIButton buttonWithType:UIButtonTypeCustom];
        [publishButton setBackgroundImage:[UIImage imageNamed:@"tabBar_publish_icon"] forState:UIControlStateNormal];
        [publishButton setBackgroundImage:[UIImage imageNamed:@"tabBar_publish_click_icon"] forState:UIControlStateHighlighted];
        [self addSubview:publishButton];
        self.publishButton = publishButton;
    }
    return self;
}

- (void)layoutSubviews
{
    [super layoutSubviews];
    
    // 设置发布按钮的frame
    self.publishButton.bounds = CGRectMake(0, 0, self.publishButton.currentBackgroundImage.size.width, self.publishButton.currentBackgroundImage.size.height);
    self.publishButton.center = CGPointMake(self.frame.size.width * 0.5, self.frame.size.height * 0.5);
    
    // 设置其他UITabBarButton的frame
    CGFloat buttonY = 0;
    CGFloat buttonW = self.frame.size.width / 5;
    CGFloat buttonH = self.frame.size.height;
    NSInteger index = 0;
    for (UIView *button in self.subviews) {
//        if (![button isKindOfClass:NSClassFromString(@"UITabBarButton")]) continue;
        if (![button isKindOfClass:[UIControl class]] || button == self.publishButton) continue;
        
        // 计算按钮的x值
        CGFloat buttonX = buttonW * ((index > 1)?(index + 1):index);
        button.frame = CGRectMake(buttonX, buttonY, buttonW, buttonH);
        
        // 增加索引
        index++;
    }
}

@end