//通过appreaance 统一设置UITabBarItem的属性    //后面带有 UI_APPEARANCE_SELECTOR 的方法 都可以通过appearance对象来统一创建    [UINavigationBar appearance];    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];    attrs[NSFontAttributeName] = [UIFont systemFontOfSize:12];    attrs[NSForegroundColorAttributeName] = [UIColor grayColor];        NSMutableDictionary *selectedAttrs = [NSMutableDictionary dictionary];    selectedAttrs[NSFontAttributeName] = [UIFont systemFontOfSize:12];    selectedAttrs[NSForegroundColorAttributeName] = [UIColor darkGrayColor];    //统一创建  [UITabBarItem appearance];    UITabBarItem *item = [UITabBarItem appearance];    [item setTitleTextAttributes:attrs forState:UIControlStateNormal];    [item setTitleTextAttributes:selectedAttrs forState:UIControlStateSelected];