[Improve Performance] ViewController for PageViewController should be initialized lazily

[muukii]

PageViewController display ViewController as full screen.
Therefore, Next or Previous ViewController should not be initialized when they before displaying.

But, Current DataSource APIs require all ViewControllers.

 func viewControllers(forPageboyViewController pageboyViewController: PageboyViewController) -> [UIViewController]?

I think that add below API likes UICollectionViewDataSource.
Example,

 func viewController(forPageboyViewController pageboyViewController: PageboyViewController, at index: Int) -> UIViewController

This API improves initialize performance when PageBoy has many viewControllers.

What do you think?

[muukii]

Or, I just have one more idea.
I think also interesting that returning factory closure for UIViewController.

[UIViewController]?

[() -> UIViewController]?

[msaps]

@muukii I agree completely. A more 'reusable' style data source would definitely be an improvement.

Have currently got it planned for v2.0.0 which I'm aiming to release in September time alongside Swift 4.0. 😄

[msaps]

Raised an issue for the changes. #88

[muukii]

@msaps
Sounds good!
I'm looking forward it.
Please let me know if I can do anything to help.

[msaps]

These changes are now available in the Pageboy 2.0 beta's 👍

Latest available here: 2.0.0 Beta 2.

Expecting final release to be available alongside Swift 4.0 support around September time.

[otymartin]

@muukii @msaps
Im experiencing this problem. In one project, the VC's load lazily - "viewDidLoad" only fires when im about to scroll to that specific VC for the first time. However in another project, all VC's are initialized at the same time (ViewDidLoad fires in all of them at launch). What could possibly cause this, both are using latest version of Pageboy/Tabman

[otymartin]

Figured out the problem

When initializing VC's for your datasource, if you perform configuration work in the initialization process, the VC will not be lazily loaded.

Eg.

var viewControllers: [UIViewController] = [] // Datasource

func loadVCS() {
 let vc = UIViewController()
vc.view.backgroundColor = .black // This ensures this VC will be loaded even if it's not yet on screen. Remove it if you want the VC to be lazily loaded (ie. When you first scroll to it).
viewControllers.append(vc)
}