[iOS] 設定 UINavigationBar 透明度

打開 - (void)viewWillAppear:(BOOL)animated

self.navigationController.navigationBar.translucent = YES;

self.navigationController.navigationBar.alpha = 0.7f;

關閉 - (void)viewWillDisappear:(BOOL)animated

self.navigationController.navigationBar.translucent = NO;

self.navigationController.navigationBar.alpha = 1.0f;