SwiftUI EXC_BAD_INSTRUCTION when filtering and mapping Array

Question

I have an Entity called Lessons, which consists of:

@NSManaged public var timeMinutes: Double
@NSManaged public var id: UUID
@NSManaged public var lessonDescription: String
@NSManaged public var date: Dates

The 'date' attribute is linked with a one-to-many relationship to a separate 'Dates' entity, which consists of:

@NSManaged public var date: Date

I am now trying to display a graph that has the summed 'timeMinutes' by 'date'. This finalArray would have the following structure:

struct FinalArray {
    let summedMinutes : Double
    let date : Date
}

My code to generate (and display) this array looks as following:

import SwiftUI
import SwiftUICharts

struct Test: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    @FetchRequest(fetchRequest: Lessons.allLessonsFetchRequest()) var lessons: FetchedResults<Lessons>

   var finalArray = [FinalArray]()

    init(){
        let allKeys = Set<Date>(lessons{$0.date.date})
        for key in allKeys {
            let sum = lessons.filter({$0.date.date == key}).map({$0.timeMinutes}).reduce(0, +)
            finalArray.append(FinalArray(summedMinutes:sum, date:key))
        }
       finalArray = finalArray.sorted(by: {$0.date < $1.date})
    }

    var body: some View {
        VStack{
               LineView(data:  finalArray.map {$0.summedMinutes}, title: "This graph returns empty").padding()
               LineView(data:  lessons.map {$0.timeMinutes}, title: "This graph works").padding()
        }
    }
}

I get the following error, on the first line of init:

Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

Does anyone know how I can fix this? What is the reason for this?

If I do a ForEach on the Core Data within my view, it works OK:

var dateFormatter: DateFormatter {
let formatter = DateFormatter()
formatter.dateStyle = .long
return formatter
}

        ForEach(lessons.map {$0.date.date}, id: \.self) { item in
            VStack{
                Text("\(item, formatter: self.dateFormatter)")
            Text(String(self.lessons.filter{$0.date.date == item}.map {$0.timeMinutes}.reduce(0, +)))
            }
        }

This code works, but it's not what I want, I want to display the summed 'timeMinutes' in an Array. Any ideas or workarounds would be super welcome!

score 0 · Accepted Answer · answered Apr 20 '20 at 04:10

The lessons is fetched on view initial update, but on init it is not defined yet, so trying to use it in there you've got a crash.

Here is possible approach:

   @State private var finalArray = [FinalArray]()

    var body: some View {
        VStack{
               LineView(data:  finalArray.map {$0.summedMinutes}, title: "This graph returns empty").padding()
               LineView(data:  lessons.map {$0.timeMinutes}, title: "This graph works").padding()
        }
        .onAppear {
           let allKeys = Set<Date>(lessons{$0.date.date})
           for key in allKeys {
               let sum = lessons.filter({$0.date.date == key}).map({$0.timeMinutes}).reduce(0, +)
               finalArray.append(FinalArray(summedMinutes:sum, date:key))
           }
          finalArray = finalArray.sorted(by: {$0.date < $1.date})
       }
    }

SwiftUI EXC_BAD_INSTRUCTION when filtering and mapping Array

1 Answers1