Can i know in viewWillAppear that it was called after navigationController pop (back button)?

Question

Say I have UIViewController A and B. User navigates from A to B with a push segue. Than user presses back button and comes to A.

Now viewWillAppear of A is called. Can I know in the code here that I came from back button (navigationController popTo...) and not by another way? And without writing special code in the B view controller.

possible duplicate of [Determine if view that appears was pushed or came from back button in navigation bar](http://stackoverflow.com/questions/20849171/determine-if-view-that-appears-was-pushed-or-came-from-back-button-in-navigation) — rmaddy, Jan 09 '14 at 03:28

score 32 · Answer 1 · answered Jan 08 '14 at 22:11

32

hm, maybe you can use self.isMovingToParentViewController in viewWillAppear, see docs, if it is NO then it means the current view controller is already on the navigation stack.

answered Jan 08 '14 at 22:11

falsecrypt

1,536
14
11

I have tried. It doesn't fit. It looks that there is no solution without writing something in B view controller.. – adsurbum Jan 10 '14 at 23:59
Yes, this worked for me!! if (self.isMovingToParentViewController) { // Do something the first time only, not on back button } – Phamer Oct 07 '14 at 18:02
2

This answer is incorrect. If the view controller is beneath the one being popped, its `isMovingToParentViewController` is always `false` when called from `viewWillAppear`. – Eric Oct 23 '15 at 10:06
Helps me a lot. – liushuaikobe Sep 11 '16 at 13:28
@Eric That's what the answer is saying. – Ruiz Jun 15 '20 at 19:26

gwest7 · Answer 2 · 2016-12-02T10:21:59.660

I like to do the following in view controller A:

- (void) viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    if (_popping) {
        _popping = false;
        NSLog(@"BECAUSE OF POPPING");
    } else {
        NSLog(@"APPEARING ANOTHER WAY");
    }

    //keep stack size updated
    _stackSize = self.navigationController.viewControllers.count;

    ....
}
- (void) viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    _popping = self.navigationController.viewControllers.count > _stackSize;

    ....
}

What you are doing is keeping track of whether your view controller (A) is disappearing because a view controller (B) is being pushed or for another reason. Then (if you did not modify the child view controller order) it should accurately tell you if (A) is appearing because of a pop on the navigation controller.

This will result in unexpected behavior if view controller A gets popped, retained, and push back onto the stack. — Ruiz, Jun 15 '20 at 19:24

score 4 · Answer 3 · answered Jan 08 '14 at 20:36

4

Add a BOOL property to UIViewController A:

@property (nonatomic) BOOL alreadyAppeared;

Then in your viewWillAppear: method, add:

if (!self.alreadyAppeared) {
    self.alreadyAppeared = YES;
    // Do here the stuff you wanted to do on first appear
}

answered Jan 08 '14 at 20:36

Gavin

8,204
3
32
42

2

But A view controller can be appeared by tab bar click also for example (it is alreadyAppeared but not called by back button) – adsurbum Jan 08 '14 at 21:37
@adsurbum I used delegate for this case in my app. – Coldsteel48 Jan 08 '14 at 22:48
This seems to be the best option for a modal view controller dismissal (I don't want `viewWillAppear` to be called). Adding this bool fixed it. – Paul Razvan Berg Apr 09 '17 at 11:03

Can i know in viewWillAppear that it was called after navigationController pop (back button)?

3 Answers3

Linked