layoutSubviews recursive called in iOS 13.2 beta1

Question

lanvsblue OP

Created Oct ’19

Replies 6

Boosts 0

Views 3.7k

Participants 2

The same code works well from iOS 9.0 to iOS 13.1.2, but stuck in iOS 13.2 beta1.

When layout subviews called, it goes recursive and cpu goes to 100%.

Step to reproduce:

1. Subclass a UITextView

2. Set some text

3. Set font or textColor in layoutSubviews method

4. Add this view to the screen

Here's the code:

#import <UIKit/UIKit.h>

@interface TYTextView : UITextView

@end


@implementation TYTextView

- (instancetype)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
self.text = @"Some text";
}
return self;
}

- (void)layoutSubviews {
[super layoutSubviews];


self.font = [UIFont systemFontOfSize:13];
self.textColor = [UIColor redColor];
}

@end

Boost

Answer 1

Claude31 OP

Oct ’19

I would suspect that if you comment out the setfont, problem disappear.

Excat ?

If so, have you set constraints on the TYTextView ?

0

Answer 2

lanvsblue OP

Oct ’19

I have set constraints on the TYTextView and if I comment out the setfont then problem disappear. Is autolayout will cause this system bug?

0

Answer 3

Claude31 OP

Oct ’19

Accepted Answer

I cannot be totally sure, but I anlyze situation as follows.

- You have constraints

- So, if OS thinks that something may change layout through those constraints, it calls systemLayout (even when nothing changes in fact, but that is what the layout engine has to check by recomputing)

- In layoutSubviews, you set the font size on an object which has constraints. That triggers a call to recompute layout, hence the infinite loop on layoutSubviews

- probably the same would occur if you set the font style to bold or normal.

That is a logical behavior, not a bug, and probably something that was improved in IOS 13.

As conclusion: don't call API that MAY change object size in layoutSubviews.

Why dont you call

self.font = [UIFont systemFontOfSize:13];

in an init or viewWillLoad for instance.

Have a look here as well :

https://stackoverflow.com/questions/40520851/how-to-avoid-infinite-layoutsubviews

with the advice :

layoutSubviews

should only ever do one thing - adjust the bounds/frames of a view's subviews. That's it. No other changes of any kind should be done there.

0

Answer 4

lanvsblue OP

Oct ’19

Thanks very much for answer

0

Answer 5

Claude31 OP

Oct ’19

From the SO thread, seems this behavior is not new to IOS13.

Don't forget to close the thread.

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Answer 6

lanvsblue OP

Oct ’19

Nope, this behavior has changed from iOS 13.2 beta.

We have at least 10k+ users and every version we published before fully test. this behavior change made our app stuck at first screen, it's very easy to reproduce.

iOS 13.0 - 13.1.2 works well, I'm sure.

0