CODEWITHSUNDEEP
swiftuiswiftdatacomputed-properties
Mink96
Mink96

Reputation: 1

How to avoid recomputations of computed properties with SwiftData's @Query in SwiftUI

With SwiftData's @Query macro, I get an array of model items. Then, I use a computed property to group the items. The computed property is used twice in my view and is therefore also computed twice. If the array is long and the operation is complex, the computed property takes a long time to be computed. How can I change my code to only compute the property once and then whenever data from @Query changes?

struct GroupListView: View {
    @Query var persons: [Person]
    
    var grouped: [[Person]] {
        // expensive operation
    }
    
    var body: some View {
        VStack {
            Text("There are \(grouped.count) groups")
            
            List {
                ForEach(grouped) { group in
                    Text("Number of members: \(group.count)")
                }
            }
        }
    }
}

I tried to store grouped as a local variable in GroupListView instead of using a computed property. The problem with this approach is that I need to declare the variable in the initializer and the view does not update when persons changes.

I also tried to store grouped as a local variable in body but this causes a recomputation whenever any state inside the view changes and not only when persons changes.

Upvotes: 0

Views: 122

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