关于ios中UIBarButtonItem 自定义 ，UITabBarControll 的隐藏

UIBarButtonItem *backItem=[[UIBarButtonItem alloc]init];
backItem.title=@" ";
UIImage *backimage=[[UIImage imageNamed:@"back.png"] resizableImageWithCapInsets:UIEdgeInsetsMake(0, 0, 0, 0)];
[backItem setBackButtonBackgroundImage:backimage forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
backimage=nil;
BszhViewControllerFirst *bszhViewController = [[BszhViewControllerFirst alloc]init];

[bszhViewController setHidesBottomBarWhenPushed：YES]//隐藏uitabbarController
self.navigationItem.backBarButtonItem=backItem;]

===折腾了一下午啊，back.png 自个用的是30*40，如果 不加红色内容，容易造成图片走形，原因未详