SOLVED: Fixing SwiftUI previews when passing a specific object in a fetch request.

@BradyR88

Jun '22

In my code I use a NavigationLink inside of a List to allow the user to drill down into different save data that they have created and I am retrieving with @FetchRequest. My preview works for the top level list by providing example data within the data controller and giving the preview access to it like this:

struct FilteredList_Previews: PreviewProvider {
    static var previews: some View {
        FilteredList(filter: "All").environment(\.managedObjectContext, DataController.preview.container.viewContext)
    }
}

The problem arises with the destination view to the navigation link. It's expecting an object to be past in that I can only get from a FetchRequest. This is lead me to attempting a solution like this:

struct ContentCard_Views_Previews: PreviewProvider {
    @FetchRequest var problems: FetchedResults<UserProblem>
    static var previews: some View {
        TitleCardView(problem: problems.first!)
            .environment(\.managedObjectContext, DataController.preview.container.viewContext)
    }
}

but as you can glean from the fact that I'm here it is not working with the error "Instance member 'problems' cannot be used on type 'ContentCard_Views_Previews'" on line 4.

Are there any good solutions to fix the PreviewProvider in this specific case? Do I need to abandon passing around specific parts of my FetchRequest and store the current selection in some sort of ViewModel, or is there a simpler way to provide example data?

P.S. ChorData not playing nice with a MVVM structure has been a huge headache if you have any advice on organizing code when interacting with this framework would be appreciated.

@BradyR88

Jun '22

The solution turns out to be providing a static variable containing an example inside my UserProblem. Which looked like this:

static var example = UserProblem(context: DataController.preview.container.viewContext)

Once this was implemented I could pass this example and to my previous provider i also no longer needed to include the environment as it only needed access to the example and nothing else.

struct ContentCard_Views_Previews: PreviewProvider {
    static var previews: some View {
        TitleCardView(problem: UserProblem.example)
    }
}

Sponsor Hacking with Swift and reach the world's largest Swift community!

Archived topic

This topic has been closed due to inactivity, so you can't reply. Please create a new topic if you need to.

All interactions here are governed by our code of conduct.