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# setNeedsUserInterfaceAppearanceUpdate()

Notifies the view controller that a change occurred that might affect the preferred interface style.

```
func setNeedsUserInterfaceAppearanceUpdate()
```

## Discussion

UIKit calls this method to let the view controller know when system-level interface style changes occur. You can also call it to let UIKit know when you change your view controller in a way that affects the preferred user interface style.

---

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