I'm trying to do a fairly simple View with MVVM to be a good ViewModel citizen. However, the code breaks while accessing the @Enviromnent Core Data in the ViewModel. I created two functions in the ViewModel. One accesses Core Data through the @Environment and one accesses Core Data with the old style - get a reference to AppDelegate and do my own thing. The OldSchool method works. Comment 2 below. The @Environment does not - it breaks at the line indicated below with an error that is not helpful for me. Comment 1. (Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0))
Now if I take the same @Environment code and put it directly into the view it Works. And if I call the same line that breaks the MVVM in a Text in the View I get the correct response. Comment 2
This is the view:
struct UserUtilities: View {
@Environment(\.managedObjectContext) var managedObjectContext
@FetchRequest(fetchRequest: DermPhoto.getAllDermPhotos()) var dermPhotos: FetchedResults<DermPhoto>
@State private var reminderInterval = 1
@State private var enableReminders = true
@State private var daysSincePhoto: Int = 0
@ObservedObject var userUtilitiesVM = UserUtilitiesViewModel()
var body: some View {
NavigationView {
VStack {
Group { //group 1
Toggle(isOn: $enableReminders) {
Text("Enable Reminders")
}
.padding(EdgeInsets(top: 50, leading: 50, bottom: 0, trailing: 50))
Text("Reminders are" + (enableReminders == true ? " On" : " Off"))
Spacer()
//Comment 3 - this always works
Text("String interpolation of self.dermPhotos.count")
Text("\(self.dermPhotos.count)")
} //group 1
Group { //group 2
Text("It has been " + "\(self.daysSincePhoto) " + (daysSincePhoto == 1 ? "day" : "days") + " since a photo was added.")
.padding(EdgeInsets(top: 0, leading: 50, bottom: 0, trailing: 50))
//options for the sentence above
//\(self.userUtilitiesVM.getTheDateInterval())
//\(self.userUtilitiesVM.getFromEnvironment())
//\(self.userUtilitiesVM.dateInterval)
Spacer()
Stepper("Reminder Interval", value: $reminderInterval, in: 1 ... 30)
.padding(EdgeInsets(top: 0, leading: 50, bottom: 0, trailing: 50))
Text("Reminder Interval is: \(reminderInterval)" + (reminderInterval == 1 ? " day" : " days"))
Spacer()
}//group 2
}
.navigationBarTitle("Reminder Days", displayMode: .inline)
.navigationBarItems(trailing: Button(action: {
print("getting the date interval from the nav button")
//self.daysSincePhoto = self.userUtilitiesVM.getOldSchool()
self.daysSincePhoto = self.userUtilitiesVM.getFromEnvironment()
//self.daysSincePhoto = self.getFromEnvironment()
} , label: { Text("Fetch")
}))
}
}
//this always works
func getFromEnvironment() -> Int {
let numberOfRecords = self.dermPhotos.count
if numberOfRecords > 0 {
let now = Date()
let lastDate = self.dermPhotos.last?.addDate
//ok to bang - addDate is always added to core data
let dateInterval = DateInterval(start: lastDate!, end: now)
let days = Int(dateInterval.duration) / (24 * 3600)
self.daysSincePhoto = days
return days
}
return 0
}
}
And this is the ViewModel:
class UserUtilitiesViewModel: ObservableObject {
@Environment(\.managedObjectContext) var managedObjectContext
@FetchRequest(fetchRequest: DermPhoto.getAllDermPhotos()) var dermPhotos: FetchedResults<DermPhoto>
@Published var dateInterval: Int = 50
//Comment 2 this always works
func getOldSchool() -> Int {
let kAppDelegate = UIApplication.shared.delegate as! AppDelegate
let context = kAppDelegate.persistentContainer.viewContext
var resultsDermPhotos : [DermPhoto] = []
let fetchRequest: NSFetchRequest<DermPhoto> = DermPhoto.fetchRequest() as! NSFetchRequest<DermPhoto>
let sortDescriptor = NSSortDescriptor(key: "addDate", ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
do {
resultsDermPhotos = try context.fetch(fetchRequest)
} catch {
print("the fetchRequest error is \(error.localizedDescription)")
}
let numberOfRecords = resultsDermPhotos.count
if numberOfRecords > 0 {
let now = Date()
let lastDate = resultsDermPhotos.last?.addDate
//ok to bang this since addDate is always added to core data
let di = DateInterval(start: lastDate!, end: now)
let days = Int(di.duration) / (24 * 3600)
dateInterval = days
return days
}
return 0
}
//this never works
func getFromEnvironment() -> Int {
//Comment 1 - this breaks
let numberOfRecords = self.dermPhotos.count
if numberOfRecords > 0 {
let now = Date()
let lastDate = self.dermPhotos.last?.addDate
//ok to bang this since addDate is always added to core data
let di = DateInterval(start: lastDate!, end: now)
let days = Int(di.duration) / (24 * 3600)
dateInterval = days
return days
}
return 0
}
}
Clearly I can use old school or abandon the ViewModel idea but I would like to know how to fix this. Any guidance would be appreciated. Xcode 11.3 (11C29)
