How do I use a property as an argument to a FetchRequest predicate - core-data

Question

I am trying to select database items with a predicate before displaying a view and need to pass a property, but I'm in a catch-22 situation since the property may not be initialized, yielding the message: Cannot use instance member 'subject' within property initializer; property initializers run before 'self' is available
struct ShowInfo: View
{
#State var subject: Subject
#Environment(\.managedObjectContext) var moc
#FetchRequest(entity: Info.entity(), sortDescriptors: [NSSortDescriptor(key: "title", ascending: true)],
predicate: NSPredicate(format: "subject.title == %#", $subject.title)
) var infos: FetchedResults<Info>
#State var size = UIScreen.main.bounds.width / 3
var body: some View
{
List
{
Text("Info").font(.system(size: 24)).foregroundColor(Color.green)
ForEach(infos, id: \.infoid)
{ info in
ZStack
{
if info.subject == self.subject.title
{
NavigationLink(destination: EditInfoView(info: info))
{
HStack
{
Text(info.title!).frame(width: 150, height: 40).background(Color.blue).foregroundColor(Color.white).cornerRadius(10)
Text(info.value!)
}
}
}
}
}.onDelete(perform: deleteInfo)
}
}
}

Answer 1

The answer found at SwiftUI View and #FetchRequest predicate with variable that can change is essentially correct, but I discovered that the order in which things appear inside the struct matters to avoid a slew of errors.
I modified my code as follows...
struct ShowInfo: View
{
init (subject: Subject)
{
self.subject = subject
self.infoRequest = FetchRequest<Info>(entity: Info.entity(), sortDescriptors: [NSSortDescriptor(key: "title", ascending: true)],predicate: NSPredicate(format: "subject.title == %#", subject.title!))
}
#Environment(\.managedObjectContext) var moc
var subject: Subject
var infoRequest: FetchRequest<Info>
var infos: FetchedResults<Info>{infoRequest.wrappedValue}
This cleared up all the errors and allowed the app to work correctly. When the init() was after the variable declarations, I got the same error as before as well as other errors. The compiler seemed to be getting confused about what had already been initialized and what had not. I'm not sure why the example shown for question 57871088 worked for others and mine required rearranging the declarations.

Answer 2

I thought the above answer solved my problem, and it did in that case, but in another view the same methodology yielded errors claiming that I hadn't initialized all the properties within the init. After much experimenting, I discovered all those errors went away if I commented out the #Environment statement. Of course that generated errors for the undefined variable moc, so I commented that code out to see what happened, then the original errors reappeared. It seems clear that the compiler is getting confused. Does anyone know a way around that issue?
Here's the code I'm working with now:
struct EditSubjectView: View
{
init(subject: Subject)
{
self.subject = subject
self.formRequest = FetchRequest(entity: Field.entity(), sortDescriptors: [NSSortDescriptor(key: "sequence", ascending: true)], predicate: NSPredicate(format: "subjectid == %#", subject.subjectid!.description))
}
#Binding var subject: Subject
var formRequest: FetchRequest<Field>
var fields : FetchedResults<Field>{formRequest.wrappedValue}
#Environment(\.managedObjectContext) var moc
var body: some View
{
return VStack
{
HStack
{
Text("Subject Title").padding(.leading)
//Spacer()
}
TextField(subject.title!, text: Binding($subject.title)!)
.padding(.all)
.background(Color(red: 239.0/255.0, green: 243.0/255.0, blue: 244.0/255.0, opacity: 1.0))
.cornerRadius(15)
Spacer()
Button("Save")
{
do
{
try self.moc.save()
}
catch
{
print(error.localizedDescription)
}
}.frame(width: 150, height: 30).background(Color.red).foregroundColor(Color.white).cornerRadius(15.0)
}.padding()
}
}