CODEWITHSUNDEEP
xcodecore-dataswiftui
Tom_Swift
Tom_Swift

Reputation: 107

SwiftUI: How to show test CoreData instanz in the preview?

I have a view that gets a core data instance as an argument:

    let timerObject: TimerObject

    var body: some View {
        Text(timerObject.name)
    }

But now of course my preview throws an error because of course it needs a value for my view:

struct TimerView_Previews: PreviewProvider {
    static var previews: some View {
        TimerView(timerObject: ???)
    }
}

if it were simple values like a string that I have to pass in then of course I can use .constant(...). Only which test value can I pass here with a core data object? Can I perhaps pass a test instance from the persistence file or something like that?

I would be very happy to hear from you! Best regards

Upvotes: 3

Views: 1148

Answers (1)

ChrisR
ChrisR

Reputation: 12125

Using the Xcode core data template, I did the following.

My model has create funcs for all objects. The principle is:

extension TimerObject {
    
    static func create(
        pos: Int = 0,         // replace with your properties
        title: String = "",
        inContext ctx: NSManagedObjectContext
    ) -> Self {
        
        let record = self.init(context: ctx)
        record.id = UUID()
        record.pos = Int16(pos)  // replace with your properties
        record.title = title

        saveContext(context: ctx)
        return record
    }
}

Then you can use those in the previews:

struct TimerView_Previews: PreviewProvider {
    static var previews: some View {

            // this is the Xcode generated preview container
            let ctx = PersistenceController.preview.container.viewContext
            let timer = TimerObject.create(pos: 0, title: "Test", inContext: ctx)

        TimerView(timerObject: timer)
            .environment(\.managedObjectContext, ctx)
   }
}

Upvotes: 5

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