Pre-initial custom UIViewController in other UIVIewController - ios

Question

I wrote a custom UIViewController for showing slide-up menu. Every time calling present(thisViewController) will show up the menu with animation and background is black transparent with alpha 0.5.
But I got problem that every first time the viewController is present, animation is not fully run, background color seems no transparent, and the slide menu is not shown the whole menu that there is one line outside of screen.
I searched the internet and found the reason is the animation not done, because the viewController is just initialed and animation is too fast shown. If I dismiss and present it
again will show as what I expected.
So I want to have a method to pre-initial the slide menu ViewController that it can run viewDidLoad before I present it. Is there a way to do this?
Update:
I call UIView.animate() in viewWillAppear(). I think the first time it ran viewWillAppear() too short time that it just initialized UIView and immediately animated, so it interrupted in the animate action. When the second time presenting this viewController, it showed the animation fully because it was shown before.
I add the views in viewDidLoad() but it won't be called until presenting the viewController.
Hmm.. I want to have a method to let the slide-up menu viewController pre-do viewDidLoad() in the other viewController.

Answer 1

#Shadowrun Thank you.
In A UIViewController, I initial the SlideMenu ViewController, and make the SlideMenu call ViewController.loadViewIfNeeded() in viewDidLoad()
class viewController: UIViewController {
var slideUpMenu = SlideMenuViewController()
override func viewDidLoad() {
super.viewDidLoad()
slideUpMenu.loadViewIfNeeded()
}
func pressButton() {
present(slideUpMenu, animated: false)
}
}
It shows perfectly.