SwiftUI and dynamic NSSortDescriptors in @FetchRequest

Question

Created Sep ’20

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I have a list with items that contain a title and a date. User can set what to sort on (title or date).

However I can't figure out how to change the NSSortDescriptor dynamically.

Code Block import SwiftUI
import CoreData
struct ContentView: View {
		@Environment(\.managedObjectContext) private var viewContext
		@FetchRequest(sortDescriptors: [NSSortDescriptor(keyPath: \Test.title, ascending: true)], animation: .default) private var items: FetchedResults<Test>
		@State private var sortType: Int = 0
		@State private var sortDescriptor: NSSortDescriptor = NSSortDescriptor(keyPath: \Test.title, ascending: true)
		var body: some View {
				Picker(selection: $sortType, label: Text("Sort")) {
						Text("Title").tag(0)
						Text("Date").tag(1)
				}
				.pickerStyle(SegmentedPickerStyle())
				.onChange(of: sortType) { value in
						sortType = value
						if sortType == 0 {
								sortDescriptor = NSSortDescriptor(keyPath: \Test.title, ascending: true)
						} else {
								sortDescriptor = NSSortDescriptor(keyPath: \Test.date, ascending: true)
						}
				}
				List {
						ForEach(items) { item in
								let dateString = itemFormatter.string(from: item.date!)
								HStack {
										Text(item.title!)
										Spacer()
										Text(dateString)
								}
						}
				}
				.onAppear(perform: {
						if items.isEmpty {
								let newEntry1 = Test(context: self.viewContext)
								newEntry1.title = "Apple"
								newEntry1.date = Date(timeIntervalSince1970: 197200800)
								let newEntry2 = Test(context: self.viewContext)
								newEntry2.title = "Microsoft"
								newEntry2.date = Date(timeIntervalSince1970: 168429600)
								let newEntry3 = Test(context: self.viewContext)
								newEntry3.title = "Google"
								newEntry3.date = Date(timeIntervalSince1970: 904903200)
								let newEntry4 = Test(context: self.viewContext)
								newEntry4.title = "Amazon"
								newEntry4.date = Date(timeIntervalSince1970: 773402400)
								if self.viewContext.hasChanges {
										try? self.viewContext.save()
								}
						}
				})
		}
}
private let itemFormatter: DateFormatter = {
		let formatter = DateFormatter()
		formatter.dateStyle = .short
		formatter.timeStyle = .none
		return formatter
}()

When I change

@FetchRequest(sortDescriptors: [NSSortDescriptor(keyPath: \Test.title, ascending: true)], animation: .default) private var items: FetchedResults<Test>

to

@FetchRequest(sortDescriptors: [sortDescriptor], animation: .default) private var items: FetchedResults<Test>

the error "Cannot use instance member 'sortDescriptor' within property initializer; property initializers run before 'self' is available" appears.

I also tried to store the NSSortDescriptor in a UserDefault and create an init that creates it's own FetchRequest.. still no dynamic sorting...

Anyone a pointer where to look to solve this problem?

Whole project found here: https://github.com/l1ghthouse/FRDSD

Answered by LH16 in 630234022

Solved! Thanks to Asperi pointing to this QA: https://stackoverflow.com/a/59345830/12299030

Code Block import SwiftUI
import CoreData
struct ContentView: View {
		@Environment(\.managedObjectContext) private var viewContext
		@AppStorage("firstLaunch") var firstLaunch: Bool = true
		@State var sortDescriptor: NSSortDescriptor = NSSortDescriptor(keyPath: \Test.title, ascending: true)
		@State private var sortType: Int = 0
		var body: some View {
				Picker(selection: $sortType, label: Text("Sort")) {
						Text("Title").tag(0)
						Text("Date").tag(1)
				}
				.pickerStyle(SegmentedPickerStyle())
				.onChange(of: sortType) { value in
						sortType = value
						if sortType == 0 {
								sortDescriptor = NSSortDescriptor(keyPath: \Test.title, ascending: true)
						} else {
								sortDescriptor = NSSortDescriptor(keyPath: \Test.date, ascending: true)
						}
				}
				ListView(sortDescripter: sortDescriptor)
				.onAppear(perform: {
						if firstLaunch == true {
								let newEntry1 = Test(context: self.viewContext)
								newEntry1.title = "Apple"
								newEntry1.date = Date(timeIntervalSince1970: 197200800)
								let newEntry2 = Test(context: self.viewContext)
								newEntry2.title = "Microsoft"
								newEntry2.date = Date(timeIntervalSince1970: 168429600)
								let newEntry3 = Test(context: self.viewContext)
								newEntry3.title = "Google"
								newEntry3.date = Date(timeIntervalSince1970: 904903200)
								let newEntry4 = Test(context: self.viewContext)
								newEntry4.title = "Amazon"
								newEntry4.date = Date(timeIntervalSince1970: 773402400)
								if self.viewContext.hasChanges {
										try? self.viewContext.save()
								}
								firstLaunch = false
						}
				})
		}
}
struct ListView: View {
		@FetchRequest var items: FetchedResults<Test>
		@Environment(\.managedObjectContext) var viewContext
		init(sortDescripter: NSSortDescriptor) {
				let request: NSFetchRequest<Test> = Test.fetchRequest()
				request.sortDescriptors = [sortDescripter]
				_items = FetchRequest<Test>(fetchRequest: request)
		}
		var body: some View {
				List {
						ForEach(items) { item in
								let dateString = itemFormatter.string(from: item.date!)
								HStack {
										Text(item.title!)
										Spacer()
										Text(dateString)
								}
						}
				}
		}
}
private let itemFormatter: DateFormatter = {
		let formatter = DateFormatter()
		formatter.dateStyle = .short
		formatter.timeStyle = .none
		return formatter
}()

Boost

Answer 1

LH16 OP

Sep ’20

Accepted Answer

Solved! Thanks to Asperi pointing to this QA: https://stackoverflow.com/a/59345830/12299030

Code Block import SwiftUI
import CoreData
struct ContentView: View {
		@Environment(\.managedObjectContext) private var viewContext
		@AppStorage("firstLaunch") var firstLaunch: Bool = true
		@State var sortDescriptor: NSSortDescriptor = NSSortDescriptor(keyPath: \Test.title, ascending: true)
		@State private var sortType: Int = 0
		var body: some View {
				Picker(selection: $sortType, label: Text("Sort")) {
						Text("Title").tag(0)
						Text("Date").tag(1)
				}
				.pickerStyle(SegmentedPickerStyle())
				.onChange(of: sortType) { value in
						sortType = value
						if sortType == 0 {
								sortDescriptor = NSSortDescriptor(keyPath: \Test.title, ascending: true)
						} else {
								sortDescriptor = NSSortDescriptor(keyPath: \Test.date, ascending: true)
						}
				}
				ListView(sortDescripter: sortDescriptor)
				.onAppear(perform: {
						if firstLaunch == true {
								let newEntry1 = Test(context: self.viewContext)
								newEntry1.title = "Apple"
								newEntry1.date = Date(timeIntervalSince1970: 197200800)
								let newEntry2 = Test(context: self.viewContext)
								newEntry2.title = "Microsoft"
								newEntry2.date = Date(timeIntervalSince1970: 168429600)
								let newEntry3 = Test(context: self.viewContext)
								newEntry3.title = "Google"
								newEntry3.date = Date(timeIntervalSince1970: 904903200)
								let newEntry4 = Test(context: self.viewContext)
								newEntry4.title = "Amazon"
								newEntry4.date = Date(timeIntervalSince1970: 773402400)
								if self.viewContext.hasChanges {
										try? self.viewContext.save()
								}
								firstLaunch = false
						}
				})
		}
}
struct ListView: View {
		@FetchRequest var items: FetchedResults<Test>
		@Environment(\.managedObjectContext) var viewContext
		init(sortDescripter: NSSortDescriptor) {
				let request: NSFetchRequest<Test> = Test.fetchRequest()
				request.sortDescriptors = [sortDescripter]
				_items = FetchRequest<Test>(fetchRequest: request)
		}
		var body: some View {
				List {
						ForEach(items) { item in
								let dateString = itemFormatter.string(from: item.date!)
								HStack {
										Text(item.title!)
										Spacer()
										Text(dateString)
								}
						}
				}
		}
}
private let itemFormatter: DateFormatter = {
		let formatter = DateFormatter()
		formatter.dateStyle = .short
		formatter.timeStyle = .none
		return formatter
}()

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