Use SwiftData @Model and ObservableObject/@Published in the same class?

Quick Fix: In the last code snippet, change the score update score += 1 to practiceData.score += 1. Directly updating a local Int variable score will not trigger SwiftUI’s observation mechanism for @Model.

The Problem:

In Swift, while working with the SwiftData library, a user is attempting to utilize both @Model and ObservableObject/@Published within the same class. They are specifically trying to implement a property ‘latestResult’ that can be observed and updated in real time within a SwiftUI view. However, the user is encountering an error when annotating ‘latestResult’ with @Published. The user is also having difficulties updating the SwiftUI view with the new value of ‘latestResult’ after modifications are made.

The Solutions:

Solution 1: Use Model as your ObservableObject

SwiftData’s `@Model` meta-data declares that the annotated class is a model object.
This gives the class special abilities, including automatic persistence and MVVM support.
The MVVM support features in `SwiftData` include:

Conformity to the `ObservableObject` protocol.

The `@Published` property wrapper.

The `@ObservableObject` property wrapper can be used to declare a property on a `View`.
When a published property inside the observed object changes, the SwiftUI view will automatically be invalidated and re-rendered.

The `@Published` property wrapper can be used to mark a property as being observable.
When the value of a published property changes, the SwiftUI view that uses that property will automatically be invalidated and re-rendered.

To use `@Model` and `@Published` in the same class:

Declare your class with the `@Model` meta-data.

Use the `@Published` property wrapper on any properties that you want to be observable.

In your SwiftUI view, use the `@ObservedObject` property wrapper to observe the model object.

When the value of a published property in the model object changes, the SwiftUI view will automatically be invalidated and re-rendered.

// PracticeData.swift

import SwiftData

@Model
final class PracticeData: ObservableObject, Codable {
    @Published var score: Int
    var results: [PracticeResult]
    @Published var latestResult: Bool?
    var trend: Float
}

// ContentView.swift

import SwiftUI
import SwiftData

struct ContentView: View {
    @ObservedObject var practiceData = PracticeData()

    var body: some View {
        VStack {
            Text("Score: \(practiceData.score)")

            Button("Increase Score") {
                practiceData.score += 1
            }
        }
    }
}

Q&A

How do I use published and @Model at the same time?

—

You don’t need to use them both, @Model also makes your class Observable.

What is my mistake in this code snippet?

—

You are updating a local variable score instead of the PracticeData.score

How do I fix my mistake?

—

Change score += 1 to practiceData.score += 1.

Video Explanation:

The following video, titled "Data Flow in a SwiftUI App - YouTube", provides additional insights and in-depth exploration related to the topics discussed in this post.

How to use @ObservableObject and @StateObject in SwiftUI | Bootcamp #50 ... Intro to SwiftData - Model, Container, Fetch, Create, Update & Delete.

Use SwiftData @Model and ObservableObject/@Published in the same class? – Swift