returned nil from -traitCollection, which is not allowed in Xcode 11 Beta

Question

Assertion failure in UITraitCollection * _Nonnull returned nil from -traitCollection, which is not allowed? when I try to run Xcode 11 beta in ios 13 it crashed. I don't know what was wrong.

Supporter

you need to add some code. From what I gather, you are maybe trying to modify a constraint's value but the IBOutlet against the same is not created or not connected. – Remissible

now I got a solution by add some code DispatchQueue.main.asyn{ //code } after featch Data – Supporter

Good to know. Glad you worked that out :) – Remissible

I have the same issue. Can you post a detailed answer? – Fore

I try to debug the class that crashed and put DispatchQueue.main.asyn{ //code } on method or statement of code that I'm Suspected​​ it will crashed one by one so the problem was solved. – Supporter

example//--Add pull to refresh DispatchQueue.main.async{self.myTableview.addSubview(self.refreshControl)} – Supporter

Same issue here, I have this assert in one of my tests when trying to initialise a UIActivityIndicatorView in the main thread... – Barneybarnhart

Answer 1

[super init]

I ran across this problem because one of the unnamed previous coders on my codebase, whom I frequently curse, didn't call [super init] on a class that implements the UITraitEnvironment (aka UIView or UIViewController)!

If I could wield a battle hammer backwards five years in time, I would.

This implementation in a subclass of UIViewController…

- (id)initWithStartPositionPdf:(float)startPosition withScrollViewHeight:(float)scrollViewHeight {
    _startPosition = startPosition;
    _scrollViewHeight = scrollViewHeight;

    self.isPdfView = YES;

    return self;
}

was updated to…

- (instancetype)initWithStartPositionPdf:(float)startPosition withScrollViewHeight:(float)scrollViewHeight {
    self = [super initWithNibName:nil bundle:nil];
    _startPosition = startPosition;
    _scrollViewHeight = scrollViewHeight;
    _isPdfView = YES;
    return self;
}

and resolved the crash I started receiving in Xcode 11 / iOS 13.

Standush

Thanks, this helped me. And also updating an app written by someone else... – Harbert

Id upvote this a million times if I could. I spent many hours trying to figure this out. Thank you. – Bronchia

Answer 2

This is how iOS 13 and Xcode 11 deal with the main thread checker inconsistencies.

basically, you are updating the UI from a background thread. Just make sure you're updating all your UI in the main thread.

Simply wrap the code that updates your UI inside DispatchQueue.main.async { }.

Vogele

Answer 3

Just simple put your code in main thread of UI update :

DispatchQueue.main.async
             {
          // Put your code here 
           }

Frisby