这是导航栏的问题，将下边的代码放在 viewWillAppear 方法中就可以实现效果：
- (void)viewWillAppear:(BOOL)animated{
// Called when the view is about to made visible. Default does nothing
[super viewWillAppear:animated];
//去除导航栏下方的横线
[navigationBar setBackgroundImage:[UIImage imageWithColor:[self colorFromHexRGB:@"33cccc"]]
forBarPosition:UIBarPositionAny
barMetrics:UIBarMetricsDefault];
[navigationBar setShadowImage:[UIImage new]];
}