导航栏透明

在要实现透明导航栏的控制器中

• viewWillAppear 中设置导航栏透明

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    
    [self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
    //去除 navigationBar 底部的细线
    self.navigationController.navigationBar.shadowImage = [UIImage new];
}

• 在viewWillDisappear 退出时还原

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [self.navigationController.navigationBar setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];
    self.navigationController.navigationBar.shadowImage = nil;
}