Скачать или смотреть How to Use NotificationCenter with Custom UIViews in Swift

Learn how to effectively notify the addition and removal of custom UIView instances using NotificationCenter in Swift, enhancing your user interface updates.
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Notification Handling with Custom UIViews in Swift

Creating dynamic user interfaces in Swift often requires custom views. These views can be added and removed from view controllers, but how do you get notified when this happens? In this guide, we’ll explore a straightforward solution to notify you when a custom UIView is presented or removed using Swift's NotificationCenter.

The Problem: Tracking View Presentation

When a custom UIView is added to or removed from its superview, you want to perform specific actions or update parts of your code accordingly. For example, you might want to trigger animations or update an application state when the view appears or disappears. The challenge arises when trying to capture these events effectively.

Here's a simplified code snippet that illustrates the creation of a custom UIView:

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You can add this view to your main view like so:

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And you can remove it by calling:

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Now, let’s tackle how to notify your code when these actions happen.

The Solution: Subclassing UIView

Using didMoveToSuperview() and willMove(toSuperview:)

The most straightforward way to track when your UIView is added or removed is by subclassing UIView and overriding its lifecycle methods. Specifically:

didMoveToSuperview(): Called whenever the view is moved to a new superview, either being added or removed.

willMove(toSuperview:): Called just before the view is moved, allowing you to react before the change occurs.

Here’s how you can implement this in your custom UIView subclass:

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Setting Up NotificationCenter

To use NotificationCenter, you need to define your notification names. Here’s how you can set it up:

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Whenever the custom view is presented or removed, these notifications will be sent. You can observe these notifications in any part of your code, like so:

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Handling the Notifications

Once you have set up the observers, respond to the notifications within your methods:

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Conclusion

Using NotificationCenter in combination with the lifecycle methods of UIView gives you a powerful way to handle events related to your custom UI components. By subclassing UIView and implementing these methods, you can easily track when your view is added or removed, allowing for better state management and user experience in your applications.

Embrace this pattern to make your Swift UI code more manageable and responsive to changes in the view hierarchy!