swift-observable

Here is the content from the Apple Developer documentation page "Migrating from the Observable Object protocol to the Observable macro" converted to Markdown format.

Migrating from the Observable Object protocol to the Observable macro

Update your existing app to leverage the benefits of Observation in Swift.

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Overview

Starting with iOS 17, iPadOS 17, macOS 14, tvOS 17, and watchOS 10, SwiftUI provides support for Observation, a Swift-specific implementation of the observer design pattern. Adopting Observation provides your app with the following benefits:

• Tracking optionals and collections of objects, which isn't possible when using ObservableObject.
• Using existing data flow primitives like State and Environment instead of object-based equivalents such as StateObject and EnvironmentObject.
• Updating views based on changes to the observable properties that a view's body reads instead of any property changes that occur to an observable object, which can help improve your app's performance.

To take advantage of these benefits in your app, you'll discover how to replace existing source code that relies on ObservableObject with code that leverages the @Observable() macro.

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Use the Observable macro

To adopt Observation in an existing app, begin by replacing ObservableObject in your data model type with the @Observable() macro. The @Observable() macro generates source code at compile time that adds observation support to the type.

BEFORE

// BEFORE
import SwiftUI

class Library: ObservableObject {
    // ...
}

AFTER

// AFTER
import SwiftUI

@Observable
class Library {
    // ...
}

Then remove the @Published property wrapper from observable properties. Observation doesn't require a property wrapper to make a property observable. Instead, the accessibility of the property in relationship to an observer, such as a view, determines whether a property is observable.

BEFORE

// BEFORE
@Observable
class Library {
    @Published var books: [Book] = [Book(), Book(), Book()]
}