Error only when the app is launched in an iPhone. Thread 1: EXC_BAD_ACCESS (code=1, address=0x4052c00000000000) - swift

Question

I am writing a program that uses data from coredata and creates a graph out of it. When I run it, it crashes with the following error Thread 1: EXC_BAD_ACCESS (code=1, address=0x4052c00000000000). The code starts from ContentView as follows
struct ContentView: View {
#State private var name = ""
#State private var score = ""
var reviewItem: ReviewItem
#State private var displayNewView = false
var body: some View {
NavigationView{
VStack {
NavigationLink(destination: ReviewView(reviewItem: ReviewItem()), isActive: self.$displayNewView) { EmptyView() }
Form {
TextField("Name", text: $name)
TextField("Score", text: $score)
}
.toolbar {
Button("add") {
reviewItem.saveReviewData(name: name, score: Int32(score)!)
self.displayNewView = true
}
}
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView(reviewItem: ReviewItem())
}
}
This is what the code for reviewView looks like
struct GradeData: Identifiable {
var id = UUID()
var averageGrade: Int32
var condition: String
}
struct ReviewView: View {
var gradeVShours: [GradeData]
init(reviewItem: ReviewItem) {
gradeVShours = [
GradeData(averageGrade: reviewItem.getScore(scoreType: "high"), condition: "Well"), GradeData(averageGrade: reviewItem.getScore(scoreType: "low"), condition: "Not Well")]
}
var body: some View {
if #available(iOS 16.0, *) {
Chart {
ForEach(self.gradeVShours) { shape in
BarMark (
x: .value("Total Grade", shape.averageGrade),
y: .value("Grade Condition", shape.condition)
)
}
}
} else {
Text("Upgrade to ios version 16.0 or higher")
}
}
}
This is what the code for ReviewItem looks like
class ReviewItem: NSObject, ObservableObject {
let coreDM: DataController = DataController.shared
override init() {
super.init()
}
func getListScore(scoreType: String) -> [Int32] {
let score = coreDM.getScoreFromCoreData(scoreType: scoreType)
return score
}
func getScore(scoreType: String) -> Int32 {
var listScore = getListScore(scoreType: scoreType)
let totalCount = scoreType.count
let totalSum = listScore.reduce(0, +)
return totalSum/Int32(totalCount)
}
func saveReviewData(name: String, score: Int32) {
coreDM.saveToCoreData(name: name, score: score)
}
}
This is what the code in DataController looks like. It is used to fetch the data from coredata. And this is where the error is thrown after the app crashes. I have noted the line where the error is thrown.
class DataController: ObservableObject {
static var shared = DataController()
let container = NSPersistentContainer(name: "StudentData")
init() {
container.loadPersistentStores(completionHandler: { description, error in
if let error = error {
print("Core data failed to laod: \(error.localizedDescription)")
}
})
}
func getScoreFromCoreData(scoreType: String) -> [Int32] {
// let filter: NSPredicate
var scoreData: [GradeTable]
var listScore: [Int32] = []
let fetchRequest: NSFetchRequest<GradeTable> = GradeTable.fetchRequest()
fetchRequest.returnsObjectsAsFaults = false
if scoreType == "high" {
let filter = NSPredicate(format: "score >= %#", 85) //Error thrown here
fetchRequest.predicate = filter
}
else {
let filter = NSPredicate(format: "score <= %#", 85)
fetchRequest.predicate = filter
}
do {
scoreData = try container.viewContext.fetch(fetchRequest)
} catch let error {
print("ERROR while fetching data from db array \(error.localizedDescription)")
return []
}
for item in scoreData {
listScore.append(item.score)
}
return listScore
}
func saveToCoreData(name: String, score: Int32) {
let gradeTable = GradeTable(context: container.viewContext)
gradeTable.uuid = UUID()
gradeTable.name = name
gradeTable.score = score
do {
try container.viewContext.save()
print("Saved")
} catch let error {
print("Error: \(error.localizedDescription)")
}
}
}
Note that StudentData has an entity named GradeTable which has attributes named score, name and uuid which is of data type Int32, string and UUID. The app launches fine and works well in simulator, but it crashes with the following error when I launch it in my phone.
I can't figure out what's going on. Using breakpoints didn't help much. Will you please tell me what's going on and how to fix it?

Answer 1

The problem is that your DataController instance will load the persistent store in an asynchronous operation, while the view immediately creates the fetch request before the persistent store is loaded completely.
You would want to move the initialization way before the view creation, such as in the SceneDelegate.

Answer 2

If you are having this issue, make sure to check the data type of the filter in Nspredicate. In my case, I was using an integer as a filter, and it was the reason behind the error. Using a string instead of an integer fixed it.
This doesn't work because the filter(85) is an integer.
let filter = NSPredicate(format: "score >= %#", 85) //Error thrown here
This works because the filter("85") is a string.
let filter = NSPredicate(format: "score >= %#", "85")