How to use #FocusedValue with optionals? - ios

Question

This question is similar to this unanswered question from the Apple Developer Forums, but with a slightly different scenario:
I have a view with a #FetchRequest property of type FetchedResults<Metric>
Within the view, I display the list of those objects
I can tap on one item to select it, storing that selection in a #State var selection: Metric? = nil property.
Here's the properties I defined for my #FocusedValue:
struct FocusedMetricValue: FocusedValueKey {
typealias Value = Metric?
}
extension FocusedValues {
var metricValue: FocusedMetricValue.Value? {
get { self[FocusedMetricValue.self] }
set { self[FocusedMetricValue.self] = newValue }
}
}
Here's how I set the focusedValue from my list view:
.focusedValue(\.metricValue, selection)
And here's how I'm using the #FocusedValue on my Commands struct:
struct MacOSCommands: Commands {
#FocusedValue(\.metricValue) var metric
var body: some Commands {
CommandMenu("Metric") {
Button("Test") {
print(metric??.name ?? "-")
}
.disabled(metric == nil)
}
}
}
The code builds successfully, but when I run the app and select a Metric from the list, the app freezes. If I pause the program execution in Xcode, this is the stack trace I get:
So, how can I make #FocusedValue work in this scenario, with an optional object from a list?

Answer 1

I ran into the same issue. Below is a View extension and ViewModifier that present a version of focusedValue which accepts an Binding to an optional. Not sure why this wasn't included in the framework as it corresponds more naturally to a selection situation in which there can be none...
extension View{
func focusedValue<T>(_ keypath: WritableKeyPath<FocusedValues, Binding<T>?>, selection: Binding<T?>) -> some View{
self.modifier(FocusModifier(keypath: keypath, optionalBinding: selection))
}
}
struct FocusModifier<T>: ViewModifier{
var keypath: WritableKeyPath<FocusedValues, Binding<T>?>
var optionalBinding: Binding<T?>
func body(content: Content) -> some View{
Group{
if optionalBinding.wrappedValue == nil{
content
}
else if let binding = Binding(optionalBinding){
content
.focusedValue(keypath, binding)
}
else{
content
}
}
}
}
In your car usage would look like:
.focusedValue(\.metricValue, selection: $selection)
I have also found that the placement of this statement is finicky. I can only make things work when I place this on the NavigationView itself as opposed to one of its descendants (eg List).

Answer 2

// 1 CoreData optional managedObject in #State var selection
#State var selection: Metric?
// 2 modifiers on View who own the list with the selection
.focusedValue(\.metricValue, $selection)
.focusedValue(\.deleteMetricAction) {
if let metric = selection {
print("Delete \(metric.name ?? "unknown metric")?")
}
}
// 3
extension FocusedValues {
private struct SelectedMetricKey: FocusedValueKey {
typealias Value = Binding<Metric?>
}
private struct DeleteMetricActionKey: FocusedValueKey {
typealias Value = () -> Void
}
var metricValue: Binding<Metric?>? {
get { self[SelectedMetricKey.self] }
set { self[SelectedMetricKey.self] = newValue}
}
var deleteMetricAction: (() -> Void)? {
get { self[DeleteMetricActionKey.self] }
set { self[DeleteMetricActionKey.self] = newValue }
}
}
// 4 Use in macOS Monterey MenuCommands
struct MetricsCommands: Commands {
#FocusedValue(\.metricValue) var selectedMetric
#FocusedValue(\.deleteMetricAction) var deleteMetricAction
var body: some Commands {
CommandMenu("Type") {
Button { deleteMetricAction?() } label: { Text("Delete \(selectedMetric.name ?? "unknown")") }.disabled(selectedMetric?.wrappedValue == nil || deleteMetricAction == nil )
}
}
}
// 5 In macOS #main App struct
var body: some Scene {
WindowGroup {
ContentView()
.environment(\.managedObjectContext, PersistenceController.shared.container.viewContext)
}
.commands {
SidebarCommands()
MetricsCommands()
}
}
Use of #FocusedValues in Apple WWDC21 example
Use of FocusedValues in SwiftUI with Majid page
Use of #FocusedSceneValue with example of action value passed, in Apple documentation

Answer 3

For SwiftUI 3 macOS Table who support multiple selections
// 1 Properties
#Environment(\.managedObjectContext) var context
var type: Type
var fetchRequest: FetchRequest<Propriete>
var proprietes: FetchedResults<Propriete> { fetchRequest.wrappedValue }
#State private var selectedProprietes = Set<Propriete.ID>()
// 2 Init from Type managedObject who own Propriete managedObjects
// #FecthRequest required to have updates in Table (when delete for example)
init(type: Type) {
self.type = type
fetchRequest = FetchRequest<Propriete>(entity: Propriete.entity(),
sortDescriptors: [ NSSortDescriptor(key: "nom",
ascending: true,
selector: #selector(NSString.localizedCaseInsensitiveCompare(_:))) ],
predicate: NSPredicate(format: "type == %#", type))
}
// 3 Table view
VStack {
Table(proprietes, selection: $selectedProprietes) {
TableColumn("Propriétés :", value: \.wrappedNom)
}
.tableStyle(BorderedTableStyle())
.focusedSceneValue(\.selectedProprietes, $selectedProprietes)
.focusedSceneValue(\.deleteProprietesAction) {
deleteProprietes(selectedProprietes)
}
}
// 4 FocusedValues
extension FocusedValues {
private struct FocusedProprietesSelectionKey: FocusedValueKey {
typealias Value = Binding<Set<Propriete.ID>>
}
var selectedProprietes: Binding<Set<Propriete.ID>>? {
get { self[FocusedProprietesSelectionKey.self] }
set { self[FocusedProprietesSelectionKey.self] = newValue }
}
}
// 5 Delete (for example) in Table View
private func deleteProprietes(_ proprietesToDelete: Set<Propriete.ID>) {
var arrayToDelete = [Propriete]()
for (index, propriete) in proprietes.enumerated() {
if proprietesToDelete.contains(propriete.id) {
let propriete = proprietes[index]
arrayToDelete.append(propriete)
}
}
if arrayToDelete.count > 0 {
print("array to delete: \(arrayToDelete)")
for item in arrayToDelete {
context.delete(item)
print("\(item.wrappedNom) deleted!")
}
try? context.save()
}
}
How to manage selection in Table