SwiftUI: Doing math in the body - swiftui

Question

I am fetching data from a Core Data store and displaying it in this view. One of these values is an integer 'duration'. I would like to display the sum of all fetched 'duration' values in the NavigaationBarTitle. But the line 'totalDuration += event.eventDuration' in the code below invokes the build-time error: 'The compiler is unable to type check this expression in a reasonable time....'. Any help is greatly appreciated.
import SwiftUI
import CoreData
struct AdminEventsLog: View {
#Environment(\.managedObjectContext) var managedObjectContext
#FetchRequest(entity: Event.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \Event.eventDate, ascending: true)]) var events: FetchedResults<Event>
var dateFormatter: DateFormatter{
let formatter = DateFormatter()
formatter.dateStyle = .short
return formatter
}
#State var showEventLogging = false
#State var totalHours: Int16 = 0
var totalDuration: Int16 = 0
var body: some View {
List{
ForEach(events){ event in
let duration = convertDuration(duration: event.eventDuration) //Converts the int
totalDuration += event.eventDuration
VStack{
HStack{
Text("Date: ")
.bold()
+ Text("\(self.dateFormatter.string(from: event.eventDate!))")
+ (Text(" Details: "))
.bold()
+ Text("\(event.eventDetails!)")
+ Text(" Dur: ").bold()
+ Text("\(duration)")
+ Text(" hrs:min")
}
HStack{
Text(" Category: ").bold()
+ Text("\(event.eventCategory!)")
}
}.font(.footnote)
}
.onDelete{ indexSet in
for index in indexSet{
self.managedObjectContext.delete(self.events[index])
}
}
}
.navigationBarTitle("Log: \(convertDuration(duration: totalHours))")
.navigationBarItems(trailing: Button(action: {
self.showEventLogging = true
print("Open ordersheet")
}, label: {
Image(systemName: "plus.circle")
.resizable()
.frame(width: 30, height: 30, alignment: .center)
})).sheet(isPresented: $showEventLogging){
EnterEvent().environment(\.managedObjectContext, self.managedObjectContext)
}
}
}
struct AdminEventsLog_Previews: PreviewProvider {
static var previews: some View {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
return AdminEventsLog().environment(\.managedObjectContext, context)
}
}

Answer 1

ForEach View isn't the same as a for each loop.
Calculate the total not in the body property, but with another computed property, from the data you have:
var totalDuration: Int {
events.reduce(0, { $0 + $1.eventDuration })
}
Then you could use it in the View:
var body: some View {
// ...
Text("\(totalDuration)")
// ...
}