Realm object update with SwiftUI

I am trying to perform updates to a realm object in a SwiftUI application but get an error when performing the update.

What special magic is required to be able to perform and update to a realm object in response to a Gesture. In the example below from here (https://docs.mongodb.com/realm/sdk/ios/integrations/swiftui/) the Toggle() is bound directly to the items property.

I need to be able to call a method to perform multiple updates in response to a gesture - the example below does not show any examples of how to perform a custom update on an observed object. Is there an example that shows how you are supposed to do that with SwiftUI ?

Would it be possible to include a simple example of doing that in the example below - just for completeness.

Thanks

/// Represents a screen where you can edit the item's name.
struct ItemDetailsView: View {
    @ObservedRealmObject var item: Item
    var body: some View {
        VStack(alignment: .leading) {
            Text("Enter a new name:")
            // Accept a new name
            TextField("New name", text: $item.name)
                .navigationBarTitle(item.name)
                .navigationBarItems(trailing: Toggle(isOn: $item.isFavorite) {
                    Image(systemName: item.isFavorite ? "heart.fill" : "heart")
                })
        }.padding()
    }
}

The error is - can’t access frozen Realm. The observable wrappers obviously take care of the updates via bindings but an example of how to do updates to the objects directly in code would be useful.

Also any discussion on whether to do updates on the main thread or not and any side effects of doing so. it seems that creating a new Realm for updates like the one below may be inefficient for very small updates so should be performed on the main thread but what is the risk of blocking the main thread.

Pretty cool though what you have done to make Realm integrate well with SwiftUI. We might have to do a rewrite sometime since it is a lot more efficient!! ouch.

Something like the following. Or if there is a more efficient way that way.

struct CheckBoxSelectionRealm: View {
    @ObservedRealmObject var item: RealmObject
    var size: CBSize
    
    var sizes: [CBSize : CGFloat] = [.small: 14, .medium: 17, .large: 21]
    
    var width: CGFloat {
        return sizes[size] ?? 17
    }
    var height: CGFloat {
        return sizes[size] ?? 17
    }
    
    var imageName: String {
        return item.isSelected ? "checkmark.square" : item.isChildSelected ? "minus.square" : "square"
    }
    var imageColor: Color {
        return item.isSelected ? Color.accentColor.opacity(0.6) : item.isChildSelected ? Color.accentColor.opacity(0.6) : Color.secondary
    }
    
    var body: some View {
        HStack {
            Text(item.name.count > 0 ? item.name : "Unlabelled")
                .foregroundColor(imageColor)
            Spacer()
            Image(systemName: imageName)
                .resizable()
                .frame(width: width, height: height)
                .foregroundColor(imageColor)
        }
        .onTapGesture {
                item.toggleSelection()
        }
    }
}

extension RealmObject {
  func toggleSelection(){
    
    /// Get object ID so we can access on another thread
    let id = self._id
    
    /// Do long running work - whatever that might be on a background thread
    DispatchQueue.global().async {
        if let realm = Realm.IAMRealm, let selfItem = realm.object(ofType: RealmObject.self, forPrimaryKey: id) {
            
            do {
                try realm.write({
                    
                    selfItem.isSelected.toggle()
                    
                    selfItem.parent?.setIsChildSelected()
                    
                })
            } catch {
                os_log(.error, "Error toggling selection for RealmObject \(self.name)")
            }
        }
    }
}
}

Thanks, yes I though the background thread was unnecessary for these small changes - and yes these items are already loaded into a list using the following - I am not doing any freeze of anything in my code. I assumed that maybe SwiftUI must be doing something. See the snippet below.

EDIT: Ah - I was using let realm = item.realm rather than your example getting a new realm = not sure if that could be the reason.

...
@ObservedResults(Taxonomies.self ) var taxonomies
...
    ScrollView {
                            VStack(alignment: .leading, spacing: 0) {
                               
                                ForEach(tax.taxonomies.sorted(byKeyPath: "name")) { group in
                                        
                                        TaxonomyGroup(group: group, spacing: 0)
                                        
                                    }
                                
                            }.padding(.leading, 4)
                            .padding(.trailing, 6)
                            //.onDelete(perform: $taxonomies.items.remove)
                            //.onMove(perform: $taxonomies.items.move)
                        }.listStyle(SidebarListStyle())

...

I just checked that when I use the items realm I get the " Can’t perform transactions on a frozen Realm" error.

If I use the following

       if let realm = Realm.IAMRealm {
             do {
                try realm.write {
                    let new = Taxonomy(name: "New Group", parent: item, isLeaf: false)
                    $item.children.append(new)
                }
             } catch {
                os_log(.error, "Error")
            }
        }

Then I get the following error:
" Cannot modify managed RLMArray outside of a write transaction."

BTW my Realm extension looks like this

extension Realm {
    static var IAMRealm: Realm? {
        let configuration = Realm.Configuration(schemaVersion: 2)
        do {
            let realm = try Realm(configuration: configuration)
            return realm
        } catch {
            os_log(.error, "Error opening realm: \(error.localizedDescription)")
            return nil
        }
    }
}

And if I try using this as per your suggestion

func toggle(){
        if let realm = Realm.IAMRealm {
             do {
                try realm.write {
                    item.isSelected = !item.isSelected
                }
             } catch {
                os_log(.error, "Error")
            }
        }
    }

I get the following error

**Attempting to modify object outside of a write transaction - call beginWriteTransaction on an RLMRealm instance first.**

And similarly this fails with the same error

func toggle2(){
        if let realm = Realm.IAMRealm {
            realm.beginWrite()
            
            item.isSelected = !item.isSelected
            
             do {
                try realm.commitWrite()
             } catch {
                os_log(.error, "Error")
            }
        }
    }

Oh and this is the top level view where it is implicitly using the default realm’s objects(Taxonomies.self). Could it be this is a problem since the system is I am using Realm.IAMRealm which uses a configuration elsewhere.

Can I get the default realm to use the same configuration somehow ? Overriding Realm.realm in an extension perhaps?

struct TaxonomyBrowserView: View {
        @ObservedResults(Taxonomies.self ) var taxonomies

....
     var body: some View {

          if let tax = taxonomies.first {
                VStack(alignment: .leading) {
                    ScrollView {
                        VStack(alignment: .leading, spacing: 0) {
                           
                            ForEach(tax.taxonomies.sorted(byKeyPath: "name")) { group in
                                    
                                    TaxonomyGroup(group: group, spacing: 0)
                                    
                                }
                            
                        }
                    }
                }
            } else {
                AnyView(Text("Setting up taxonomies..."))
    ...

So if I need to do a few things, like creating a new item and adding it then I need to use the complex way.

let new = Taxonomy(name: "New Group", parent: item, isLeaf: false)
$item.children.append(new)

What I don’t understand is why your example shows adding children to a list without going through any hoops. What am I doing differently that this does not work. Is it because my items are in a list already and if I want to add an item to their children I can’t. It seems counterintuitive that at the same time you can modify the item directly when bound to a detail view (as per example). Is the RealmSwift taking care of thawing the object under the covers ?

I never did watch Ice Age 2 !

struct ItemsView: View {
    /// The group is a container for a list of items. Using a group instead of all items
    /// directly allows us to maintain a list order that can be updated in the UI.
    @ObservedRealmObject var group: Group

    /// The button to be displayed on the top left.
    var leadingBarButton: AnyView?
    var body: some View {
        NavigationView {
            VStack {
                // The list shows the items in the realm.
                List {
                    ForEach(group.items) { item in
                        ItemRow(item: item)
                    }.onDelete(perform: $group.items.remove)
                    .onMove(perform: $group.items.move)
                }.listStyle(GroupedListStyle())
                    .navigationBarTitle("Items", displayMode: .large)
                    .navigationBarBackButtonHidden(true)
                    .navigationBarItems(
                        leading: self.leadingBarButton,
                        // Edit button on the right to enable rearranging items
                        trailing: EditButton())
                // Action bar at bottom contains Add button.
                HStack {
                    Spacer()
                    Button(action: {
                        **// The bound collection automatically**
**                            // handles write transactions, so we can**
**                            // append directly to it.**
**                            $group.items.append(Item())**
                        }) { Image(systemName: "plus") }
                    }.padding()
                }
            }
        }
    }

Great these work just fine - a lot less complex than unnecessary background tasks ! But using Sync mainly I am used to doing that for most things anyway.