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How to delete Core Data objects from SwiftUI views

Paul Hudson    @twostraws   

Updated for Xcode 12.0

Deleting Core Data objects in SwiftUI is mostly the same as deleting them in UIKit, although there are a couple of special hoops to jump through to integrate with SwiftUI’s views.

If you followed my Core Data and SwiftUI set up instructions, you’ve already injected your managed object context into the SwiftUI environment.

Once you have your managed object context, make it available to your SwiftUI view as a property like this one:

@Environment(\.managedObjectContext) var managedObjectContext

Next, create a fetch request that reads some data from your managed object context. In my example setup there’s a ProgrammingLanguage entity, so we can read out all items like this:

@FetchRequest(
    entity: ProgrammingLanguage.entity(),
    sortDescriptors: [
        NSSortDescriptor(keyPath: \ProgrammingLanguage.name, ascending: true),
    ]
) var languages: FetchedResults<ProgrammingLanguage>

Third, add an onDelete modifier to your SwiftUI view, wherever you’re showing your data. For example, using the above fetch request you might create a list using ForEach, like this:

List {
    ForEach(languages, id: \.self) { language in
        Text("Creator: \(language.creator ?? "Anonymous")")
    }.onDelete(perform: removeLanguages)
}

Finally, add the removeLanguages() method to your SwiftUI view. This should accept an IndexSet, which is a collection of unique integer indexes that should be deleted:

func removeLanguages(at offsets: IndexSet) {
    for index in offsets {
        let language = languages[index]
        managedObjectContext.delete(language)
    }
}

You might want to save your Core Data context at this point, in which case after the for loop finishes add something like this:

do {
    try managedObjectContext.save()
} catch {
    // handle the Core Data error
}

Just adding an onDelete modifier is enough to get swipe to delete on your table rows, but if you also want an Edit/Done button to toggle editing mode you should add this modifier to whatever is directly inside your NavigationView:

.navigationBarItems(trailing: EditButton())
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