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. You probably have adopted that tutorial, it’s best 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 enormously simplify the method of defining information mannequin and retrieving data from the database, making it extraordinarily simple for builders to deal with persistent information.
The Preview characteristic 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 learn how to combine SwiftData with SwiftUI Preview successfully.
Word: In case you 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:
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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 routinely allow persistence for the info class.
To be able to drive the info operations (like replace, insert, learn, and delete), we additionally must arrange the mannequin container. Within the ToDoDemoAppApp.swift, we now have 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 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:
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struct ContentView: View { @Atmosphere(.modelContext) non-public var modelContext
@Question var todoItems: [ToDoItem]
var physique: some View { NavigationStack { Listing { ForEach(todoItems) { todoItem in HStack { Textual content(todoItem.identify)
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 record as a result of the container doesn’t have any information populated. In case you want to have some pattern information, 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 = 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.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 record view with 10 random objects.
Abstract
SwiftUI Preview is a beneficial characteristic that permits builders to visualise their app’s person interface immediately, with out the necessity to launch the simulator. This tutorial gives complete steerage on successfully utilizing SwiftData with SwiftUI Preview. You must learn to create a customized container populated with pattern information particularly for preview functions.
In case 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 e-book 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. Observe me at Fb, Twitter and Google+.
