viewWillAppear not firing for UIViewController that belongs to UITabBarController until I switch tabs

Question

In my iOS app, I have a UITabBarController, and its viewControllers list looks like [vc1, vc2], which are of class MyVC1 and MyVC2 respectively, both of which subclass UIViewController. MyVC1 overrides viewWillAppear, and the overwritten version prints something so I know when it is called. (This is to isolate a larger problem I had, which was a view not appearing.)

My issue is that when the app first starts up and vc1 is the selected tab, nothing is printed, meaning its viewWillAppear is not being called. If I switch tabs and then go back to vc1, something does get printed, so vc1's viewWillAppear is not being called until I switch back to it from another tab.

Is there any way to have vc1 call viewWillAppear as soon as the app starts up, without needing to switch tabs? Honestly, I'm surprised this wasn't the default behavior already.

score 21 · Accepted Answer · answered Sep 10 '16 at 10:59

I just made a new test app in Xcode with nothing but a UITabViewController (and its two child view controllers) in Main.storyboard, and when I override viewWillAppear for the first child, my "view will appear" log prints every time (including on app launch).

Here are a couple things that could cause viewWillAppear to not be called:

Not calling super somewhere you've overridden viewWillAppear
Adding a view controller's view somewhere as a subview without adding the view controller as a child view controller

You also might try seeing if viewWillAppear is getting called for your UITabBarController, and if not, is it being called for its parent or presenting view controller? And so on until you find where the holdup is.

Thanks, I overrode the `viewWillAppear` of `UITabBarController` without calling `super.viewWillAppear` inside. Stupid mistake... — BallpointBen, Sep 12 '16 at 01:50
I Appreciate this answer. It's a very small thing and normally we miss it. It saved a lot of time. Thanks — Mitesh Khatri, Sep 18 '21 at 11:05

score 4 · Answer 2 · answered Feb 21 '19 at 08:56

4

if you have Custom UITabBarController, check override func viewWillAppear is call super

in Custom UITabBarController

override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated) // this line need
    }

answered Feb 21 '19 at 08:56

sdo

71
4

oh,... i see comment. – sdo Feb 21 '19 at 08:57

score 1 · Answer 3 · answered Sep 10 '16 at 04:38

1

Use the following line in viewWillAppear method of your vc1:

  [super viewWillAppear:animated];

Next, the UITabBarController must be your initial controller.

answered Sep 10 '16 at 04:38

KSR

1,699
15
22

Sorry, that didn't help. It's still not getting called until I switch to `vc1` from another tab. – BallpointBen Sep 10 '16 at 05:42
Can u post a screenshot of your storyboard? – KSR Sep 10 '16 at 10:07
2

Thanks for your help. The missing call to super was in my `UITabBarController`. – BallpointBen Sep 12 '16 at 01:51
What do I do if UITabBarController isn't my initial controller? – michaeldebo Nov 17 '20 at 19:00

score 0 · Answer 4 · answered Aug 16 '18 at 08:28

0

make shure in the UITabBarController in the viewwillapear have the super.viewWillAppear(animated) like the following code

override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

    }

answered Aug 16 '18 at 08:28

Ala'a AbuNemeh

149
5

viewWillAppear not firing for UIViewController that belongs to UITabBarController until I switch tabs

4 Answers4

Linked