viewIsAppearing(_:) — A New Addition to “UIViewController” class in iOS

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In Swift, view controllers are responsible for managing views and how they appear on the screen. We’ve been using several view lifecycle methods like:

viewWillAppear(_), viewDidAppear(_), viewWillDisappear(_), and viewDidDisappear(_)

iOS calls these methods at different points in the view controller’s lifecycle.

This quick post explores a new addition to the view lifecycle methods: viewIsAppearing(_)

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`viewIsAppearing(_)` in iOS 17

Introduced in iOS 17 and Xcode 15, `viewIsAppearing(_)` is a new method added to the `UIViewController` class. It’s designed to help us fine-tune how our views look when they become visible.

The Sequence in the View Lifecycle

• viewWillAppear(_:): This method is called first, indicating that the view will appear soon, but its size and position might not be final.
• View Updates: The view gets its final layout and position.
• viewIsAppearing(_): This method is called after the view has its final dimensions.

Use case

The ideal use cases for `viewIsAppearing(_)` are when you need to make UI adjustments that depend on the most up-to-date information about the view’s size and location on the screen.

For example, if you have an image that needs to resize itself perfectly to fit within the view’s bounds, `viewIsAppearing(_)` is the ideal place to do that because you’re guaranteed to have the most accurate size information at that point.

Here’s a Quick Comparison

| Method           | When It's Called            | Use For                   |
|------------------|-----------------------------|---------------------------|
| `viewWillAppear` | Before the view appears,    | Actions before animations |
|                  | layout might be preliminary |eg: setting up transitions |
|                  |                             |                           |
| `viewIsAppearing`| After the view has its final| UI adjustments based on   |
|                  | layout and position         | final view size & position|

Sample Code

class MyViewController: UIViewController {

  override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    print("View will appear (layout might be preliminary)")
  }

  override func viewIsAppearing(_ animated: Bool) {
    super.viewIsAppearing(animated)
    print("View is appearing (layout is finalized)")
  }
}

Conclusion

The viewIsAppearing(_:) function is a valuable addition for making UI adjustments based on the view’s final state. You can use it alongside viewWillAppear(_:) to manage different aspects of the view’s appearance. Give it a try in your project and see how it enhances your UI management.

Happy coding!