How do I execute a SectionedFetchRequest in a SwiftUI Preview? - core-data

Question

Previously, I was using FetchRequest and passing the results to my view. I had this working in my preview using the following code:
struct SchoolsGrid_Previews: PreviewProvider {
static var viewContext = PersistenceController.preview.container.viewContext
static var fetchRequest = School.fetchRequest()
static func getSchools() -> [School] {
do {
return try viewContext.fetch(fetchRequest)
} catch {
print(error.localizedDescription)
return []
}
}
static var previews: some View {
SchoolsGrid(sectionedSchools: Dictionary(
grouping: getSchools(),
by: {
$0.name!.first!.isLetter ? String($0.name!.first!) : "#"
}
))
.environment(\.managedObjectContext, viewContext)
.environmentObject(SettingsData())
}
}
After learning about SectionedFetchRequest, I updated my code and my view to accept this instead, but I am unable to find the "sectioned" alternative to the code above. I tried the following without any luck - it returns no data:
struct SchoolsGrid_Previews: PreviewProvider {
static var viewContext = PersistenceController.preview.container.viewContext
static var fetchRequest = SectionedFetchRequest(fetchRequest: School.fetchRequest(), sectionIdentifier: \School.firstLetterOfName)
static var previews: some View {
SchoolsGrid(sectionedSchools: fetchRequest.wrappedValue)
.environment(\.managedObjectContext, viewContext)
.environmentObject(SettingsData())
}
}
Edit to add:
I have a wrapper view which fetches my data, because the same data can be presented in two different subviews - SchoolsGrid and SchoolsList:
struct Schools: View {
#State var isGrid = false
#State var searchTerm: String = ""
#SectionedFetchRequest<String, School>(
entity: School.entity(),
sectionIdentifier: \.firstLetterOfName,
sortDescriptors: [
NSSortDescriptor(keyPath: \School.name, ascending: true),
]
) var sectionedSchools: SectionedFetchResults<String, School>
var query: Binding<String> {
Binding {
searchTerm
} set: { newValue in
searchTerm = newValue
let namePredicate = NSPredicate(format: "%K CONTAINS[c] %#", #keyPath(School.name), newValue)
sectionedSchools.nsPredicate = newValue.isEmpty
? nil
: namePredicate
}
}
var body: some View {
NavigationView {
ScrollViewReader { _ in
VStack {
ZStack {
if isGrid {
SchoolsGrid(sectionedSchools: sectionedSchools, searchTerm: searchTerm)
} else {
SchoolsList(sectionedSchools: sectionedSchools, searchTerm: searchTerm)
}
}
}
.searchable(text: query)
}
.navigationTitle("Schools")
.toolbar {
ToolbarItemGroup(placement: .navigationBarTrailing) {
Button(action: { isGrid.toggle() }) {
Image(systemName: isGrid ? "list.bullet" : "square.grid.2x2")
.accessibilityLabel("Toggle View")
}
}
}
}
}
}
My SchoolsGrid looks like:
struct SchoolsGrid: View {
var sectionedSchools: SectionedFetchResults<String, School>
var searchTerm: String
var gridItems: [GridItem] {
Array(repeating: .init(.adaptive(minimum: 120)), count: 2)
}
var body: some View {
ScrollView {
ForEach(sectionedSchools) { section in
Section(header: SchoolsGridSectionHeader(key: section.id)) {
LazyVGrid(columns: gridItems) {
ForEach(section) { school in
NavigationLink(destination: SchoolDetail(school: school)) {
SchoolsGridItem(school: school, searchTerm: searchTerm)
}
}
}
}
}
}
}
}
And my SchoolsList:
struct SchoolsList: View {
var sectionedSchools: SectionedFetchResults<String, School>
var searchTerm: String
var body: some View {
List {
ForEach(sectionedSchools) { section in
Section(header: Text(section.id).id(section.id)) {
ForEach(section) { school in
NavigationLink(destination: SchoolDetail(school: school)) {
SchoolsListItem(school: school, searchTerm: searchTerm)
}
}
}
}
}
.listStyle(PlainListStyle())
}
}
As with the first part of my question, I only recently changed the fetch request to a sectioned fetch request, so previously both SchoolsGrid and SchoolsList accepted schools: FetchResults< School> and I was able to emulate this in the Preview using the first code block, where I used viewContext.fetch. After updating to accept sectionedSchools: SectionedFetchResults<String, School>, there is no viewContext.sectionedFetch that I can use, so passing it the way I tried using:
var fetchRequest = SectionedFetchRequest(fetchRequest: School.fetchRequest(), sectionIdentifier: \School.firstLetterOfName)
returns no data because it isn't being called on the preview view context.