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. In case you have adopted that tutorial, you need to 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 tremendously simplify the method of defining information mannequin and retrieving information from the database, making it extraordinarily straightforward for builders to deal with persistent information.
The Preview function in SwiftUI is very useful 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 the way to combine SwiftData with SwiftUI Preview successfully.
Be aware: When you haven’t learn the SwiftData tutorial, I extremely suggest 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 now have constructed a mannequin class for ToDoItem like this:
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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 routinely allow persistence for the info class.
With a purpose 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 connected the modelContainer modifier like under:
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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 now have a ContentView that hundreds and shows the to-do merchandise within the listing view. Right here is the pattern code:
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struct ContentView: View { @Surroundings(.modelContext) personal var modelContext
@Question var todoItems: [ToDoItem]
var physique: some View { NavigationStack { Listing { ForEach(todoItems) { todoItem in HStack { Textual content(todoItem.title)
Spacer()
if todoItem.isComplete { Picture(systemName: “checkmark”) } } } }
.navigationTitle(“To Do Listing”) } } } |
You may 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 listing as a result of the container doesn’t have any information populated. When you need to have some pattern information, you possibly can 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 = attempt 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.rely) let randomTask = duties[randomIndex]
return ToDoItem(title: 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 listing view with 10 random objects.
Abstract
SwiftUI Preview is a useful function that enables builders to visualise their app’s person interface immediately, with out the necessity to launch the simulator. This tutorial offers 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 take pleasure in studying this tutorial and wish to study extra about SwiftUI, don’t overlook to take a look at our Mastering SwiftUI ebook for iOS 17 and Xcode 15.
Founding father of AppCoda. Creator 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+.