透明导航栏

方法一

[self.navigationController.navigationBar setBackgroundImage:[UIImage new]
                                                  forBarMetrics:UIBarMetricsDefault];
    self.navigationController.navigationBar.shadowImage = [UIImage new];

方法二

self.imageViewBar = self.navigationController.navigationBar.subviews.firstObject;
self.imageViewBar.alpha = 0;