修改tabbar的高度

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

    CGRect frame = self.tabBar.frame;
    frame.size.height = 具体的高度值 0/49;
    frame.origin.y = self.view.frame.size.height - frame.size.height;
    self.tabBar.frame = frame;
    self.tabBar.backgroundColor = [UIColor clearColor];
    self.tabBar.barStyle = UIBarStyleBlack;
}