Determine viewWillAppear from Popped UINavigationController or UITabBarController - ios

Question

I am unable to find a way to distinguish between popping from the Nav controller stack and entering the view controller from the UITabBarController.
I want to call a method in ViewWillAppear only when the view is presented from the TabBar, not when someone presses back in the navigation controller.
If I wasn't using a TabBarController, I could easily get this functionally using viewDidLoad.
I've tried,
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
println("View Will Appear")
if isBeingPresented() {
println("BP")
}
if isMovingFromParentViewController() {
println("from")
}
if isMovingToParentViewController() {
println("to")
}
}
But there is no difference when I present from pressing the Tab Button or when press back button.
Only the "View Will Appear" is getting called.
Using iOS 8.4 / Swift

Answer 1

Sounds like a good use of the UITabBarControllerDelegate.
First, add a Bool property on your ViewController comingFromTab:
class MyViewController: UIViewController {
var comingFromTab = false
// ...
}
Set your UITabBarControllerDelegate to whatever class you want and implement the method shouldSelectViewController. You may also want to subclass UITabBarController and put them in there.
func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {
if let myViewController = viewController as? MyViewController {
myViewController.comingFromTab = true
}
If your tab's initial view controller is a UINavigationController, you will have to unwrap that and access it's first view controller:
if let navController = viewController as? UINavigationController {
if let myViewController = navController.viewControllers[0] as? MyViewController {
// do stuff
}
}
Lastly, add whatever functionality you need in viewWillAppear in your view controller:
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
// ...
if comingFromTab {
// Do whatever you need to do here if coming from the tab selection
comingFromTab = false
}
}

Answer 2

There is no way to know for sure. So I guess the easiest way is to add some variable that you will have to change before popping back to that view controller and checking it's state in viewWillAppear.
class YourViewController: UIViewController {
var poppingBack = false
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
if !poppingBack {
// your logic
}
else {
poppingBack = false // reset it for next time
}
}
}
// somewhere else in code, suppose yourVC is YourViewController
yourVC.poppingBack = true
self.navigationController.popToViewController(yourVC, animated: true)
You can also try implementing UINavigationControllerDelegate's - navigationController:willShowViewController:animated: method and check if it will be called when presenting your view controller from tab bar.

Answer 3

You can check parentViewController property
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
if parentViewController is UITabBarController {
// Presented by UITabBarController
} else if parentViewController is UINavigationController {
// Presented by UINavigationController
} else {
// Presented by ...
}
}