//在页面显示时将透明打开
-(void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:animated];
[self.navigationController.navigationBar.subviews firstObject].hidden = YES;
}
//关闭时显示
-(void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
[self.navigationController.navigationBar.subviews firstObject].hidden = NO;
}