Push页面隐藏tabor,Pop回来自动显示tabbar

//2.如果在push跳转时需要隐藏tabBar，设置self.hidesBottomBarWhenPushed=YES;

    self.hidesBottomBarWhenPushed=YES;
    NextViewController *next=[[NextViewController alloc]init];
    [self.navigationController pushViewController:next animated:YES];
    self.hidesBottomBarWhenPushed=NO;

//并在push后设置self.hidesBottomBarWhenPushed=NO;
//这样back回来的时候，tabBar会恢复正常显示。