In Day 78 challenge ( SaveContact App) I have added a detail view that when an item on the list is tapped it will navigate in a view that shows the Image on the top and the annotated Map at the bottom. The view works, but, when I try to pan on the map the map is sluggish.. For the image I am using a computable Image variable, that reads the .jpg file from the disk. Debugging, I noticed that if I just place an image and place it in Assets.xcassets and try to load it in the detail view with the map, the map works flawlessy! Did someone notice something similar ? Below is my detail view code in case you notice something too obvious..

import SwiftUI
import MapKit

struct ItemDetailView: View {

    var itemName: String
    var itemImage: Image {
        let uiImage = (UIImage(data: try! Data(contentsOf: FileManager.documentsDirectory.appendingPathComponent("\(itemName).jpg")))!)
        return Image(uiImage: uiImage)
    }

    @ObservedObject var viewModel = ContentView.ViewModel() //My viewModel is an extension of the ContentView
    var imageLocationLatidude: Double
    var imageLocationLongitude: Double

    var body: some View {
        VStack {
            itemImage.resizable().scaledToFit().clipShape(RoundedRectangle(cornerRadius: 20)).padding()
//            Image("sample").resizable().scaledToFit().clipShape(RoundedRectangle(cornerRadius: 20)).padding() //This works perfectly with the map.
            //***Map Start
            Map(coordinateRegion: $viewModel.mapRegion, annotationItems: viewModel.contacts) { _ in
                MapMarker(coordinate: CLLocationCoordinate2D(latitude: imageLocationLatidude, longitude: imageLocationLongitude))
            }.clipShape(RoundedRectangle(cornerRadius: 20)).padding(.horizontal)
            //Map End***
        }
        .onAppear { // I use the code below to re-center the map at location of the annotation.
            viewModel.mapRegion = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: imageLocationLatidude, longitude: imageLocationLongitude), span: MKCoordinateSpan(latitudeDelta: 25, longitudeDelta: 25))
        }
    }
}

@Ostrich observes:

So, every time you move the map a slight amount,
the View would have to reload itself and compute the property
(render the image from data) again.

Oh nice! I've always wanted to find a reason to learn how to use the Instruments application provided with Xcode. One of the instruments is a disk access monitor. This might be a great use case to test!

If it works the way I think it should, you launch Instruments and watch your application whilst it's running in the simulator. Perhaps as you pan around the map, you might, as @Ostrich predicts, you might see a ton of data being loaded and reloaded. This might be a great way to test this assumption!

I guess the reloading of the Image is the culprit.. How do I stop it from reloading all the time? Maybe if I make a separate View for the map and add that one in the Vstack?

You could probably do it by just declaring itemImage as an Image without initializing it. So, it would no longer be a computed property. Then you would need to write a custom initializer for ItemDetailView that takes care of initializing itemImage.

Thanks for the help guys. The computable variable was the reason for the poor performance..I just moved the computation of the UIImage into the NavigationLink (in my contentView) ItemDetailView Struct and issue solved, no more constant reloading of the image..