UICollectionView的透明UINavigationBar问题

Question

I've created a simple project to test how to make UINavigationBar transparent. In this project I have two UIViewController. The first view controller shows a big button which push the second view controller into navigation controller.

The second view controller is a UIViewController which contains an UICollectioView (it isn't a UICollectionViewController).

In the app delegate I wrote this code into application:didFinishLaunchingWithOptions

UINavigationBar.appearance().setBackgroundImage(UIImage(), forBarMetrics: .Default)
UINavigationBar.appearance().shadowImage = UIImage()
UINavigationBar.appearance().backgroundColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.0)
UINavigationBar.appearance().translucent = true

It works like a charm for the first UIViewController (the navigation bar is transparent), but when I move to the other UIViewController (with UICollectionView) the navigation bar is not transparent and when I come back to previous UIViewController still remains not transparent!

Any suggestion?

PS: Just to be clear, my expected result is that I want to see cells even when I scroll up and they pass under the navigation bar. I don't know if I was clear.

Answer 1

As i do not have 50 reputation yet i cannot comment on the question, but i replicated your project in Xcode and i found no errors. I got the following screens (notice the translucent navigation bar):

To create these screens the following actions where taken so this is where something could have gone wrong:

• Add code to AppDelegate
• Embed FirstViewController in NavigationController
• Add SecondViewController
• Add button to FirstViewController
• Add segue between 'Button' and SecondViewController
• Add CollectionView to SecondViewController
• Add Constraints to 'Button' and 'CollectionView'

This might sound stupid but in the AppDelegate did you place your code before the:

return true

statement?

Answer 2

I spent 24 hours to figure out the problem! It was a stupid bad constraint! The UICollectionView had a constraint to the Top Layout Guide instead of View of UIViewController!