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 Knowledge. You probably have adopted that tutorial, it is best to now be acquainted with utilizing SwiftData to avoid wasting and handle knowledge in a database. The built-in @Mannequin macro and the @Question macro vastly simplify the method of defining knowledge mannequin and retrieving data from the database, making it extraordinarily straightforward for builders to deal with persistent knowledge.
The Preview function in SwiftUI is extremely beneficial because it permits builders to immediately visualize the app’s person interface with out the necessity to launch the simulator. Nevertheless, utilizing SwiftData with SwiftUI Preview requires some further steps. On this tutorial, we are going to discover easy methods to combine SwiftData with SwiftUI Preview successfully.
Notice: For those who haven’t learn the SwiftData tutorial, I extremely advocate checking it out first, as this tutorial references a number of the supplies lined in that tutorial.
Revisiting the Knowledge Mannequin and SwiftData
Within the earlier instance, we’ve constructed a mannequin class for ToDoItem like this:
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import Basis import SwiftData
@Mannequin class ToDoItem: Identifiable { var id: UUID var identify: String var isComplete: Bool
init(id: UUID = UUID(), identify: String = “”, isComplete: Bool = false) { self.id = id self.identify = identify 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 mechanically allow persistence for the info class.
With a view to drive the info operations (like replace, insert, learn, and delete), we additionally must arrange the mannequin container. Within the ToDoDemoAppApp.swift, we’ve connected the modelContainer modifier like beneath:
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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’ve a ContentView that hundreds and shows the to-do merchandise within the checklist view. Right here is the pattern code:
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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.identify)
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:
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#Preview { ContentView() .modelContainer(for: ToDoItem.self) } |
Nevertheless, on this case, the preview solely shows an empty Todo checklist as a result of the container doesn’t have any knowledge populated. For those who need to have some pattern knowledge, you may create a customized mannequin container particularly for the preview. Right here is an instance:
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@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(“Didn’t 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..<duties.depend) let randomTask = duties[randomIndex]
return ToDoItem(identify: randomTask, isComplete: Bool.random()) } |
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:
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#Preview { ContentView() .modelContainer(previewContainer) } |
When you made the modification, the preview pane ought to present you the Todo checklist view with 10 random objects.
Abstract
SwiftUI Preview is a beneficial function that enables builders to visualise their app’s person interface immediately, with out the necessity to launch the simulator. This tutorial gives complete steering on successfully utilizing SwiftData with SwiftUI Preview. You must learn to create a customized container populated with pattern knowledge particularly for preview functions.
For those who take pleasure in studying this tutorial and wish to study extra about SwiftUI, don’t overlook to take a look at our Mastering SwiftUI guide for iOS 17 and Xcode 15.
Founding father of AppCoda. Writer of a number of iOS programming books together with Starting iOS Programming with Swift and Mastering SwiftUI. iOS App Developer and Blogger. Comply with me at Fb, Twitter and Google+.