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 substitute for Core Information. When you have adopted that tutorial, you must now be accustomed to utilizing SwiftData to save lots of and handle information in a database. The built-in @Mannequin macro and the @Question macro vastly 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 function in SwiftUI is very helpful because it permits builders to immediately visualize the app’s consumer 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 combine SwiftData with SwiftUI Preview successfully.

Be aware: For those who haven’t learn the SwiftData tutorial, I extremely suggest checking it out first, as this tutorial references among the supplies coated in that tutorial.

Revisiting the Information 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 have to mark the mannequin class with the @Mannequin macro. SwiftData will then mechanically allow persistence for the info class.

To be able to drive the info operations (like replace, insert, learn, and delete), we additionally have to arrange the mannequin container. Within the ToDoDemoAppApp.swift, we now have hooked up the modelContainer modifier like beneath:

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

This configuration is basically 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 hundreds and shows the to-do merchandise within the record view. Right here is the pattern code:

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

    @Question var todoItems: [ToDoItem]

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

                        Spacer()

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

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

You may 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. For those who want to have some pattern information, you possibly can 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 helpful function that permits builders to visualise their app’s consumer interface immediately, with out the necessity to launch the simulator. This tutorial supplies complete steering on successfully utilizing SwiftData with SwiftUI Preview. It’s best to learn to create a customized container populated with pattern information particularly for preview functions.

For those who get pleasure from studying this tutorial and need to study extra about SwiftUI, don’t neglect to take a look at our Mastering SwiftUI ebook for iOS 17 and Xcode 15.