Run a function located in one UIViewController from a different controller - ios

Question

I currently have two UIViewControllers, a Calculation UIViewController, and a Settings UIViewController. I'm attempting to make a dark and light theme. In the Calculation VC, I have a theme function:
func setCandyTheme() {
print("Theme enabled!")
configureGradientBackground(UIColor(red: 0.14, green: 0.85, blue: 1.0, alpha: 0.8).CGColor, UIColor(red: 0.24, green: 0.65, blue: 1.0, alpha: 0.8).CGColor)
for view: UIView in containerViews {
view.backgroundColor = UIColor(red: 1, green: 1, blue: 1, alpha: 0.18)
}
for textField: UITextField in textFields {
textField.backgroundColor = UIColor(red: 1.0, green: 1.0, blue: 1.0, alpha: 0.20)
}
for textField: UITextField in weightTextFields {
textField.backgroundColor = UIColor(red: 1.0, green: 1.0, blue: 1.0, alpha: 0.25)
}
}
In the Settings VC, I made a toggle for enabling the theme. When it's enabled, it sets the themeKey value (which works) and runs the setCandyTheme function.
func switchIsChanged(themeToggle: UISwitch) {
let storyBoard = UIStoryboard(name: "Main", bundle: nil)
let calcViewController = storyBoard.instantiateViewControllerWithIdentifier("Calculate") as! ViewController
if themeToggle.on {
defaults.setValue("True", forKey: themeKey.key)
calcViewController.setCandyTheme()
}
else {
defaults.setValue("False", forKey: themeKey.key)
}
}
Unfortunately, the theme isn't applied but the "Theme enabled!" string is printed in the console. I assume it's running the function in the Settings VC rather than Calculation, which is why it's not being applied.
What's the solution for this? I've been at it for hours and any help would be much appreciated!

Answer 1

When you do the following, you are creating a new instance of that ViewController. Therefore, you are running your code on that other instance, not the one that is attached to the screen. Therefore, you are not changing what you think you are changing.
let calcViewController = storyBoard.instantiateViewControllerWithIdentifier("Calculate") as! ViewController
You can have ViewControllers call functions in other ViewControllers but you have to give it the ViewController to call, you cannot instantiate a new one.
You could just store the current theme in your AppDelegate or someplace like that. Then, when the calculator viewWillAppear fires, adjust the theme as needed.

Answer 2

I ended up finding a solution! The calculation view controller was not being refreshed after a self.dismissViewControllerAnimated(false, completion: nil), so what I ended up doing was create an Unwind Segue and set the theme in the function.
#IBAction func unwindToCalculation(segue: UIStoryboardSegue) {
if themeOn == defaults.stringForKey(themeKey.key) {
self.setCandyTheme()
}
}