SwiftUI with Core Data getting Blank Screen in simulator in Xcode 12

Question

In XCode 12, if I create a new SwiftUI App and check the "Use Core Data" button, the resulting application (with no changes) shows a blank screen in simulator (as well as on a device). In preview it shows the example timestamps as expected. Why are the simulator/device not showing the example timestamps?

We'd love to help, but with so little to go on, any answer would be guesswork. Please edit your question to give more information: does it happen for all apps, or only one app? Has it always happened, or has it started happening? What's your code? — pbasdf, Sep 22 '20 at 08:00
Still a problem in Xcode 12.4 I submitted feedback https://openradar.appspot.com/radar?id=4939835114520576 — malhal, Jan 29 '21 at 12:31

uplearned.com · Answer 1 · 2021-01-01T05:23:58.210

The toolbar items default code is broken in SwiftUI: Use this in the template code. Embed the List into a NavigationView and then The buttons in a HStack.

var body: some View {
    NavigationView { //added
    List {
        ForEach(items) { item in
            Text("Item at \(item.timestamp!, formatter: itemFormatter)")
        }
        .onDelete(perform: deleteItems)
    } .toolbar {
        
                    #if os(iOS)
                    HStack {  //added
                        EditButton()
                        Button(action: addItem) {
                            Label("Add Item", systemImage: "plus")
                        }
                    }//added
                    #endif

    }
    }//added NavView embed
}

Also to get the preview to work you need to change the PersistenceController to shared not preview.

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView().environment(\.managedObjectContext, PersistenceController.shared.container.viewContext)
    }
}

score 5 · Answer 2 · answered Oct 19 '20 at 05:49

5

If you want to see the sample inputs from the template (10 rows with timestamp) in your simulator, you need to change in App.swift:

let persistenceController = PersistenceController.shared

to

let persistenceController = PersistenceController.preview

Without this change, the template provided by Apple shows the sample input only in the canvas preview of ContentView. The Persistence.swift file has two static variables: shared and preview. The .shared one is just initiating an (empty) PersistenceController while the .preview static variable initiates a PersistenceController, adds ten items with the current time stamp to the viewContext and saves it.

answered Oct 19 '20 at 05:49

L-vis

51
3

Indeed. But I guess the core issue is that the simulator shows no control to add items. – Pierre Mardon Nov 05 '20 at 10:17
1

I wrapped the List in ContentView in a NavigationView and each of the button of the toolbar modifier in a ToolBarItem. After that, I can see the Edit and the Add button as NavigationBarButtons in my simulator and can add items with these controls. – L-vis Nov 09 '20 at 03:51

score 1 · Answer 3 · answered Sep 24 '20 at 21:01

Clearing the data in the simulator did not work for me.

I'm struggling with .toolbar but find it only works with a NavigationView in the released XCode 12.

So if you're using the template that comes when you click to use Core Data, just add to the ContentView.

score 0 · Answer 4 · answered Sep 22 '20 at 08:50

0

clearing the data in simulator under "Device->Erase all content and settings" worked for me

answered Sep 22 '20 at 08:50

Sai Durga Mahesh

205
2
13

Great @SaiDurgaMahesh – Dc7 Sep 22 '20 at 10:24

SwiftUI with Core Data getting Blank Screen in simulator in Xcode 12

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