How to Use Codable in Swift for Effective State Restoration in iOS Apps

Описание: Learn how to implement `Codable` and `NSCoding` for state restoration in your Swift applications to easily save and restore user data.
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This video is based on the question https://stackoverflow.com/q/63429909/ asked by the user 'Z S' ( https://stackoverflow.com/u/145552/ ) and on the answer https://stackoverflow.com/a/63429989/ provided by the user 'matt' ( https://stackoverflow.com/u/341994/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Use Codable in Swift for Effective State Restoration in iOS Apps

In the world of iOS development, ensuring a seamless user experience is crucial, especially when it comes to maintaining application state. Users expect that when they leave your app — whether it be by pressing the home button or if the system forces it to close — they can return to the same state they left off. This is where State Restoration comes into play.

In this guide, we’ll address a specific problem: how to implement state restoration using the Codable protocol in Swift, particularly within a controller that stores various user filters.

Understanding the Problem

You have an iOS app with a view controller that manages several types of filters. When the user applies filters and then leaves the app, you want to ensure that their selections are saved and restored when they return. The question arises: How can we achieve this with Swift's Codable protocol, especially since we need to integrate it with an Objective-C based UIViewController?

The Initial Setup

Let’s first take a look at the Swift class you are working with:

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You also have an Objective-C class that manages the state restoration:

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And the logic for state restoration:

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Attempting to encode the CJDataViewControllerFilters directly crashes the app with the message indicating a selector issue. This suggests that the class requires a proper encoding mechanism.

The Solution: Implement NSSecureCoding

Step 1: Conforming to NSSecureCoding

To resolve the issue, you should conform the CJDataViewControllerFilters class to NSSecureCoding. This will enable you to use a keyed archiver for saving the filters state effectively.

Here’s how to implement the changes:

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Step 2: Managing Complex Properties

For properties like NSPredicate and NSManagedObject, you’ll find that most built-in types already conform to NSSecureCoding. Thus, you simply need to encode and decode them using the NSCoder methods.

For NSManagedObject: Ensure that it’s being managed by a proper Core Data context to avoid issues during state restoration.

Step 3: Handling Other Codable Properties

If you have properties that are Codable but do not directly conform to NSCoding, you can make use of methods like encodeEncodable(_:forKey:) and decodeDecodable(_:forKey:).

Conclusion

By implementing NSSecureCoding within your CJDataViewControllerFilters class, you can effectively maintain state across user sessions in your iOS application. This seamless restoration of user filters not only enhances user experience but also builds a more robust app.

With these steps, you can confidently approach state restoration challenges in iOS. Теперь ваш пользовательский интерфейс и данные фильтров будут сохранены и восстановлены без проблем!