Question: Suppose I have a nav controller stack with 2 view controllers: VC2 is on top and VC1 is underneath. Is there code I can include in VC1 that will detect that VC2 has just been popped off the stack? 

Since I'm trying to detect the popping of VC2 from within the code for VC1 it seems that something like **viewWillAppear** or **viewDidAppear** won't work, because those methods fire every time VC1 is displayed, including when it is first pushed on the stack.

**EDIT:** it seems I was not very clear with my original question. Here's what I'm trying to do: determine when VC1 is being shown due to VC2 being popped off the top of the stack. Here's what I'm NOT trying to do: determine when VC1 is being shown due to being pushed onto the top of the stack. I need some way that will detect the first action but NOT the second action. 

Note: I don't particularly care about VC2, it can be any number of other VCs that get popped off the stack, what I do care about is when VC1 becomes the top of the stack again due to some other VC begin popped off the top.

Answer: 
swift 3

```
override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        if self.isMovingToParentViewController {
            print("View is moving to ParentViewControll")
        }
}

```
You can add an observer for NSNotification specifically JUST for your VC2.

```
// pasing the "VC2" here will tell the notification to only listen for notification from
// VC2 rather than every single other objects
[[NSNotitificationCenter defaultCenter] addObserver:self selector:@selector(doSomething:) object:VC2];

```

Now in in your VC2's view will disappear, you can post a notification:

```
-(void)viewWillDisappear
{
    [[NSNotificationCenter defaultCenter] postNotificationNamed:@"notif_dismissingVC2" object:nil];
}

```