content
    .onPreferenceChange(SizeKey.self, perform: { sizes in
        // this is not always called
    })
    .overlayPreferenceValue(SizeKey.self) { sizes in
        EmptyView().onAppear {
            // this is called more reliably
            // the view's id controls for which changes this is called
        }.id(sizes.map { $0.width*1000+$0.height })
    }