SwiftUI How to pass CoreData object to an other view [duplicate]

Preview canvas is is crashing but in simulator everything working fine. I assuming it related to @ObservedObject and @Fetchrequest...

tried solution for here Previewing ContentView with CoreData

doesn't work

 import SwiftUI
 import CoreData

struct TemplateEditor: View {

@Environment(\.managedObjectContext) var managedObjectContext

@FetchRequest(
    entity: GlobalPlaceholders.entity(),
    sortDescriptors: [
        NSSortDescriptor(keyPath: \GlobalPlaceholders.category, ascending: false),
    ]
) var placeholders: FetchedResults<GlobalPlaceholders>


@ObservedObject var documentTemplate: Templates
@State private var documentTemplateDraft = DocumentTemplateDraft()
@Binding var editing: Bool


var body: some View {

    VStack(){
        HStack(){
            cancelButton
            Spacer()
            saveButton
        }.padding()
        addButton
        ForEach(placeholders)  {placeholder in
            Text(placeholder.name)
        }
        TextField("Title", text: $documentTemplateDraft.title)

        TextField("Body", text: $documentTemplateDraft.body)
            .padding()
            .frame(width: 100, height:400)
        Spacer()
    }

...




}
struct TemplateEditor_Previews: PreviewProvider {
    static var previews: some View {

    let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Templates")
    request.sortDescriptors = [NSSortDescriptor(keyPath: \Templates.created, ascending: false)]
    let documentTemplate = try! managedObjectContext.fetch(request).first as! Templates


    return TemplateEditor(documentTemplate: documentTemplate, editing: .constant(true)).environment(\.managedObjectContext, managedObjectContext).environmentObject(documentTemplate)

    }
}

Expected to generate preview

Solution 1:

I'm not sure if your try line will work if there is no data.

let documentTemplate = try! managedObjectContext.fetch(request).first as! Templates

To get mine to work I created a test Item to use. Like this:

struct DetailView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
//Test data
        let newEvent = Event.init(context: context)
        newEvent.timestamp = Date()
        return DetailView(event: newEvent).environment(\.managedObjectContext, context)
    }
}

I've also noticed that I needed the .environment(.managedObjectContext, context) code in an earlier tabView that hosted the CoreData views or the preview would fail.

Solution 2:

This answer seems to work in my recent project by replacing the default ContentView_Previews struct, though others are questioning whether it pulls persistent data. Credit goes to @ShadowDES - in the Master/Detail template project in Xcode Beta 7

I'm able to CRUD anything using Canvas (XCode Version 11.3 (11C29)) and it seems to run flawlessly.

    #if DEBUG
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        return ContentView().environment(\.managedObjectContext, context)
    }
}
#endif