Updating a @Binding value without triggering changes

Question

I have a struct which's init is like that

@Binding var fieldValue:Float

init(fieldValue:Binding<Float>) {
  self._fieldValue = fieldValue
}

at some point I would like to update fieldValue without triggering updates on other points listening to $fieldValue.

Is that possible?

Answer 1

The problem is that SwiftUI synchronizes all Bindings by default and there's no way to explicitly disable this behaviour.

However, we can work around it by wrapping the property in an ObservableObject and get a custom Binding based on the behaviour that is desired, using the Binding(get:set:) initializer.

(Note that this may not work well with the standard UI components, like Slider, as they may expect a Binding update in order to work correctly.)

class ValueContainer: ObservableObject {
    
    private var fieldValue: Float = 0
    
    func getBinding(isTriggering: Bool) -> Binding<Float> {
        Binding { [self] in
            self.fieldValue
        } set: { [self] newValue in
            self.fieldValue = newValue
            if isTriggering {
                self.objectWillChange.send()
            }
        }
    }
    
}

struct DoesNotTriggerUpdate: View {
    
    @ObservedObject var container: ValueContainer
    
    var body: some View {
        Slider(value: container.getBinding(isTriggering: false))
    }

}

struct DoesTriggerUpdate: View {
    
    @ObservedObject var container: ValueContainer
    
    var body: some View {
        Slider(value: container.getBinding(isTriggering: true))
    }

}