icon-image 渲染模式
UIImageRenderingModeAlwaysTemplate：带有tintColor 的渲染模式
UIImageRenderingModeAlwaysOriginal：展示图片的原来样式
[image imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
icon-image 位置调整
图片设置过大，覆盖文字调整图片边距： self.imageInsets = UIEdgeInsetsMake(-10, 0, 10, 0);
特别要注意的是:
top和bottom要设置成相反数，不然image的大小会一直改变
文字颜色设置
[self setTitleTextAttributes:[NSDictionary
dictionaryWithObjectsAndKeys: [UIColor colorWithRed:100.0 / 255.0 green:100.0 / 255.0 blue:100.0 / 255.0 alpha:1],
NSForegroundColorAttributeName, nil] forState:UIControlStateSelected];
[self setTitleTextAttributes:[NSDictionary
dictionaryWithObjectsAndKeys: [UIColor brownColor],
NSForegroundColorAttributeName, nil] forState:UIControlStateNormal];
隐藏topLine
[self.tabBar setShadowImage:[UIImage new]];
设置tabBar背景图片
self.tabBar.backgroundImage = [UIImage imageNamed:@"cm2_btm_bg"];