iOS Navigationbar在pop时出现黑块怎么解决

一般会在次级页面重写viewWillAppear和viewWillDisappear，具体代码如下：

• (void)viewWillAppear:(BOOL)animated
  {
  [super viewWillAppear:animated];
  [self.navigationController setNavigationBarHidden:YES animated:YES];
  }
• (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[self.navigationController setNavigationBarHidden:NO animated:YES];
}