shadowByte
shadowByte

Reputation: 133

Previews crashing when using with core-data

I am trying to create a simple task to-do application with swiftui and core-data however, I am running into some problems when adding views. I have a TaskView view that will be used to show some info about the task within the list (title, date, etc.). However, when trying to create a preview for the view with a demo Task object the preview crashes (running app still works).

Sorry if this is a trivial question, new to swift and programming in general.

TaskView.swift

import SwiftUI

struct TaskView: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    
    var task: Task
    
    var body: some View {
        HStack {
            Image(systemName: task.checked == true ? "circle" : "checkmark.circle.fill")

            VStack {
                Text(task.name ?? "unknown name")
                Text(String(task.streak))
            }
        }
    }
}

struct TaskView_Previews: PreviewProvider {
    static var previews: some View {
        let task = Task()
        task.name = "Washing up"
        task.desc = "Wash the dishes"
        task.checked = false
        task.streak = 2
        
        return TaskView(task: task)
            .previewLayout(.fixed(width: 375, height: 60))
    }
}

ContentView.swift

import SwiftUI

struct ContentView: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    @FetchRequest(entity: Task.entity(), sortDescriptors: [
        NSSortDescriptor(keyPath: \Task.checked, ascending: false),
        NSSortDescriptor(keyPath: \Task.name, ascending: true)
    ]) var tasks: FetchedResults<Task>
    
    var body: some View {
        NavigationView {
            List {
                ForEach(tasks, id: \.self) { task in
                    TaskView(task: task).environment(\.managedObjectContext, self.managedObjectContext)
                }
                .onDelete(perform: deleteTask)
            }
            .navigationBarTitle("Today")
        }
    }
    
    func deleteTask(at indexSet: IndexSet) {
        indexSet.forEach { TaskUtils.delete(task: tasks[$0], using: self.managedObjectContext)}
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Upvotes: 1

Views: 119

Answers (1)

NotAPhoenix
NotAPhoenix

Reputation: 166

I fixed your TaskView by adding first setting a context constant and then using init in initialising the task constant that you are using in the preview

import SwiftUI

struct TaskView: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    
    var task: Task
    
    var body: some View {
        HStack {
            Image(systemName: task.checked == true ? "circle" : "checkmark.circle.fill")

            VStack {
                Text(task.name ?? "unknown name")
                Text(String(task.streak))
            }
        }
    }
}

struct TaskView_Previews: PreviewProvider {
    
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext // IMPORTANT
        let task = Task.init(context: context) // IMPORTANT
        task.name = "Washing up"
        task.desc = "Wash the dishes"
        task.checked = false
        task.streak = 2
        
        return TaskView(task: task).environment(\.managedObjectContext, context)
            .previewLayout(.fixed(width: 375, height: 60))
    }
}

As for your ContentView, I made minor changes to get it working- added a button to add objects to the CoreData model.

import SwiftUI

struct ContentView: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    @FetchRequest(entity: Task.entity(), sortDescriptors: [
        NSSortDescriptor(keyPath: \Task.checked, ascending: false),
        NSSortDescriptor(keyPath: \Task.name, ascending: true)
    ]) var tasks: FetchedResults<Task>
    
    var body: some View {
        NavigationView {
            List {
                ForEach(tasks, id: \.self) { task in
                    TaskView(task: task).environment(\.managedObjectContext, self.managedObjectContext)
                }
                //.onDelete(perform: deleteTask)
            }
            .navigationBarTitle("Today")
            .navigationBarItems(trailing:
                Button("Add") {
                    let task = Task(context: self.managedObjectContext)
                    task.name = "Washing up"
                    task.desc = "Wash the dishes"
                    task.checked = false
                    task.streak = Int32(Int.random(in: 0...10))
                    
                    try? self.managedObjectContext.save()
                }
            )
        }
    }
    
//    func deleteTask(at indexSet: IndexSet) {
//        indexSet.forEach { TaskUtils.delete(task: tasks[$0], using: self.managedObjectContext)}
//    }
}

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

Upvotes: 1

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