tabbar item的字体大小和颜色, 在appdelegate指定根控制器时即可添上以下两句
[[UITabBarItem appearance] setTitleTextAttributes:@{ NSForegroundColorAttributeName:kRGBColor(102, 102, 102),
NSFontAttributeName:[UIFont systemFontOfSize:10.5 * SCALE_WIDTH]
} forState:UIControlStateNormal];
[[UITabBarItem appearance] setTitleTextAttributes:@{ NSForegroundColorAttributeName:kRGBColor(102, 102, 102),
NSFontAttributeName:[UIFont systemFontOfSize:10.5 * SCALE_WIDTH]
} forState:UIControlStateSelected];