Override traitCollection of UIView

Question

I am using a UIView with a nib as a template for a UIImage that I am generating, and I want to handle the output of the iPad in landscape differently than portrait. The best way I have figured I can do that is by setting up my landscape view for horizontal Regular, vertical Compact traits in the nib and assigning those traits before generating the image.

I have tried using the performAsCurrent method which successfully changes the UITraitCollection.current value but does not affect my UIView traitCollection property, and I have tried overriding the traitCollection getter in the UIView class which returns the error:

Class overrides the -traitCollection getter, which is not supported. If you're trying to override traits, you must use the appropriate API.

Is there a way to do this for a UIView that is never drawn to the screen?

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Posted by

aharriscrowne

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Answer 1

The only supported APIs for changing the horizontal/vertical size class traits are the following:

UIPresentationController overrideTraitCollection https://developer.apple.com/documentation/uikit/uipresentationcontroller/1618335-overridetraitcollection

UIViewController setOverrideTraitCollection(_:forChild:) https://developer.apple.com/documentation/uikit/uiviewcontroller/1621406-setoverridetraitcollection

There isn't a way to change/override the size class traits of a UIView, so you will need to use one of the above APIs with the view inside of a view controller (and/or presentation), or modify your UIView's code to avoid using the size class traits directly and instead base its layout on your own properties which you control.

Posted by

Frameworks Engineer

Thanks for the great feedback. I have switched to nesting my UIView in a UIViewController which I then add as a child view controller to another controller. I can successfully override the child view controller's trait collection, but the child view controller's view trait collection property does not seem to inherit the change and so when I call layoutIfNeeded(), the layout does not reflect the new trait collection. Can you suggest how to ensure the child view controller's view inherits the setOverrideTraitCollection change?

—
aharriscrowne
Interestingly, if I override traitCollectionDidChange in my child view controller, add a breakpoint there, and print the traitCollection of its view in the debugger, it shows the inherited traitCollection correctly and then proceeds to lay out the view properly. But unless I do that print, the value stays the old one for the child view controller's view.

—
aharriscrowne

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Answer 2

The only supported APIs for changing the horizontal/vertical size class traits are the following:

UIPresentationController overrideTraitCollection https://developer.apple.com/documentation/uikit/uipresentationcontroller/1618335-overridetraitcollection

UIViewController setOverrideTraitCollection(_:forChild:) https://developer.apple.com/documentation/uikit/uiviewcontroller/1621406-setoverridetraitcollection

There isn't a way to change/override the size class traits of a UIView, so you will need to use one of the above APIs with the view inside of a view controller (and/or presentation), or modify your UIView's code to avoid using the size class traits directly and instead base its layout on your own properties which you control.

Posted by

Frameworks Engineer

Thanks for the great feedback. I have switched to nesting my UIView in a UIViewController which I then add as a child view controller to another controller. I can successfully override the child view controller's trait collection, but the child view controller's view trait collection property does not seem to inherit the change and so when I call layoutIfNeeded(), the layout does not reflect the new trait collection. Can you suggest how to ensure the child view controller's view inherits the setOverrideTraitCollection change?

—
aharriscrowne
Interestingly, if I override traitCollectionDidChange in my child view controller, add a breakpoint there, and print the traitCollection of its view in the debugger, it shows the inherited traitCollection correctly and then proceeds to lay out the view properly. But unless I do that print, the value stays the old one for the child view controller's view.

—
aharriscrowne

Add a Comment

Override traitCollection of UIView

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