Utilizing SwiftData with Preview in SwiftUI

Within the earlier tutorial, I’ve walked you thru the fundamentals of SwiftData, a brand new framework launched in iOS 17 as a alternative for Core Knowledge. When you’ve got adopted that tutorial, you need to now be accustomed to utilizing SwiftData to avoid wasting and handle information in a database. The built-in @Mannequin macro and the @Question macro significantly simplify the method of defining information mannequin and retrieving information from the database, making it extraordinarily simple for builders to deal with persistent information.

The Preview characteristic in SwiftUI is very priceless because it permits builders to immediately visualize the app’s person interface with out the necessity to launch the simulator. Nonetheless, utilizing SwiftData with SwiftUI Preview requires some extra steps. On this tutorial, we’ll discover tips on how to combine SwiftData with SwiftUI Preview successfully.

Be aware: When you haven’t learn the SwiftData tutorial, I extremely advocate checking it out first, as this tutorial references a few of the supplies lined in that tutorial.

Revisiting the Knowledge Mannequin and SwiftData

Within the earlier instance, we now have constructed a mannequin class for ToDoItem like this:

import Basis
import SwiftData

@Mannequin class ToDoItem: Identifiable {
    var id: UUID
    var title: String
    var isComplete: Bool

    init(id: UUID = UUID(), title: String = "", isComplete: Bool = false) {
        self.id = id
        self.title = title
        self.isComplete = isComplete
    }
}

SwiftData simplifies the method of defining a schema utilizing code. You solely must mark the mannequin class with the @Mannequin macro. SwiftData will then routinely allow persistence for the information class.

With a purpose to drive the information operations (like replace, insert, learn, and delete), we additionally must arrange the mannequin container. Within the ToDoDemoAppApp.swift, we now have hooked up the modelContainer modifier like under:

struct ToDoDemoAppApp: App {
    var physique: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(for: ToDoItem.self)
    }
}

This configuration is actually all you want earlier than beginning to work with SwiftData.

Preview with SwiftData and In-memory Container

Within the Todo app demo, we now have a ContentView that masses and shows the to-do merchandise within the record view. Right here is the pattern code:

struct ContentView: View {
    @Atmosphere(.modelContext) personal var modelContext

    @Question var todoItems: [ToDoItem]

    var physique: some View {
        NavigationStack {
            Checklist {
                ForEach(todoItems) { todoItem in
                    HStack {
                        Textual content(todoItem.title)

                        Spacer()

                        if todoItem.isComplete {
                            Picture(systemName: "checkmark")
                        }
                    }
                }
            }

            .navigationTitle("To Do Checklist")
        }
    }
    }

You can also make the preview work by writing the preview code like this:

#Preview {
    ContentView()
        .modelContainer(for: ToDoItem.self)
}

Nonetheless, on this case, the preview solely shows an empty Todo record as a result of the container doesn’t have any information populated. When you want to have some pattern information, you may create a customized mannequin container particularly for the preview. Right here is an instance:

@MainActor
let previewContainer: ModelContainer = {
    do {
        let container = strive ModelContainer(for: ToDoItem.self,
                                           configurations: .init(isStoredInMemoryOnly: true))

        for _ in 1...10 {
            container.mainContext.insert(generateRandomTodoItem())
        }

        return container
    } catch {
        fatalError("Did not create container")
    }
}()

func generateRandomTodoItem() -> ToDoItem {
    let duties = [ "Buy groceries", "Finish homework", "Go for a run", "Practice Yoga", "Read a book", "Write a blog post", "Clean the house", "Walk the dog", "Attend a meeting" ]

    let randomIndex = Int.random(in: 0..

We instantiate a ModelContainer with an in-memory configuration and populate the container with 10 random to-do objects. To make use of this preview container, you merely modify the preview code and specify to make use of the previewContainer:

#Preview {
    ContentView()
        .modelContainer(previewContainer)
}

When you made the modification, the preview pane ought to present you the Todo record view with 10 random objects.

Abstract

SwiftUI Preview is a priceless characteristic that permits builders to visualise their app’s person interface immediately, with out the necessity to launch the simulator. This tutorial supplies complete steering on successfully utilizing SwiftData with SwiftUI Preview. You must discover ways to create a customized container populated with pattern information particularly for preview functions.

When you get pleasure from studying this tutorial and wish to be taught extra about SwiftUI, don’t neglect to take a look at our Mastering SwiftUI guide for iOS 17 and Xcode 15.