Calling func of another view controller to control alpha returns nil error

Question

I have a (parent) view controller that has a container view within it. When app is started, it first goes to the parent, then it goes into the container view. Within the container view controller I try something like parentName().changeAlpha() - this is a function belonging to the parent... which should change the alpha of a label on the parent view.

However, it keeps giving me a nil error as soon as I attempt to call that function. Please keep in mind the parent view is being loaded first thing.

Hierarchy: (I have the Xcode name of each controller followed by the file name belonging to it in parenthesis)

Tab Bar Controller (TabBarController) (There are 3 tabs)

Tab1 (homeScreenContainer) - Contains a view controller with a uiviewcontainer within it. Also contains the function that I am trying to call.

All part of container view:

• Page View Controller (2 Pages total, first page is the one below) (RootPageViewController)

  • View controller (ViewController) - this is where I am trying to call the function.

---

Tab2 (Irrelevant)

Tab3 (Irrelevant)

Also, the only inheritance in both the code and the storyboard is only the uiviewcontainer (and there is no code inheritance involved there).

Answer 1

Doing this

parentName().changeAlpha()

Creates another object of parent other than the shown one , and it gives nil error as the VC should be loaded from Stroyboard/Xib not like this parentName() except if it's programmatically created , what you really need is querying the window for it , suppose the parent is the rootVC of the window you can do this

if let tab = UIApplication.shared.keyWindow?.rootViewController as? UITabBarController {
      print("Inside Tap")
   if let realParent = tab.viewControllers![0] as? ParentVC {
     print("Inside Parent")
     realParent.changeAlpha()
   }
}