Running out of memory while fetching images from Photos SwiftUI

Question

I am working on an app that can detect dog breeds, and I would like to make it when users pull up their photo library, they only see images with a dog. To do this, I used the Vision pet recognizer model which is very basic, the issue is that it takes a while and too much memory to run on 1000s of photos. I was wondering if there were any solutions.

PhotoLibraryViewModel.swift

import Photos
import UIKit
import Vision

class PhotoLibraryViewModel: ObservableObject {
    
    @Published var uiImages = [UIImage]()
    var allPhotos : PHFetchResult<PHAsset>? = nil
        
    init() {
        getPhotos()
    }
    
    private func getPhotos() {
        PHPhotoLibrary.requestAuthorization { [weak self] status in
            switch status {
            case .authorized:
                let fetchOptions = PHFetchOptions()
                fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
                self?.allPhotos = PHAsset.fetchAssets(with: .image, options: fetchOptions)
                self?.setCompositionalLayout()
            case .denied, .restricted:
                print("Not allowed")
            case .notDetermined:
                print("Not determined yet")
            case .limited:
                print("limited")
            @unknown default:
                fatalError()
            }
        }
    }
    
    private func setCompositionalLayout() {
        print("all photos: " + "\(allPhotos!.count)")
        
        allPhotos?.enumerateObjects() { [self] photo, _, _  in
            
            
            
            let options = PHImageRequestOptions()
            options.version = .original
            
            PHImageManager.default().requestImage(for: photo, targetSize: CGSize(width: (screen.width - 60) / 3, height: (screen.width - 60) / 3), contentMode: PHImageContentMode.aspectFit, options: options) { [self] uiImage, _ in
                
                guard let finalUIImage = uiImage else {
                    print("failed to make finalUIImage")
                    return
                }
                
                checkImage(uiImage: finalUIImage)

            }
        }
    }
    
    private func checkImage(uiImage: UIImage) {
        
        var animalRecognitionRequest = VNRecognizeAnimalsRequest(completionHandler: nil)
        
        let animalRecognitionWorkQueue = DispatchQueue(label: "PetClassifierRequest", qos: .userInteractive, attributes: [], autoreleaseFrequency: .workItem)
        
        guard let cgImage = uiImage.cgImage else {
            print("failed to convert image")
            return
        }
        
        animalRecognitionWorkQueue.async {
            let requestHandler = VNImageRequestHandler(cgImage: cgImage, options: [:])
            do {
                try requestHandler.perform([animalRecognitionRequest])
            } catch {
                print("error: " + "\(error)")
            }
        }
        
        animalRecognitionRequest = VNRecognizeAnimalsRequest { [self] request, error in
            if let results = request.results as? [VNRecognizedObjectObservation] {
                for result in results {
                    let animals = result.labels
                    
                    for animal in animals {
                        if animal.identifier == "Dog" {
                            DispatchQueue.main.async {
                                uiImages.append(uiImage)
                                print("dog detected")
                            }
                            continue
                        }
                    }
                }
            }
        }
    }
}

PhotoLibraryView.swift

import SwiftUI

struct PhotoLibraryView: View {
    @StateObject var photoLibraryViewModel = PhotoLibraryViewModel()
    
    var body: some View {
        
        NavigationView {
            ZStack {
                LinearGradient(gradient: Gradient(colors: [Color(#colorLiteral(red: 0.2588235438, green: 0.7568627596, blue: 0.9686274529, alpha: 1)), Color(#colorLiteral(red: 0.2392156869, green: 0.6745098233, blue: 0.9686274529, alpha: 1))]), startPoint: .top, endPoint: .bottom)
                    .edgesIgnoringSafeArea(.all)
                
                ScrollView {
                    // Compositional Layout....
                    LazyVGrid(columns: Array(repeating: GridItem(.flexible(), spacing: 15), count: 3)) {
                        ForEach(0..<photoLibraryViewModel.uiImages.count, id: \.self) { index in
                            Image(uiImage: photoLibraryViewModel.uiImages[index])
                                .resizable()
                                .frame(width: (screen.width - 60) / 3, height: (screen.width - 60) / 3)
                                .cornerRadius(13)
                        }
                    }
                    .padding(.horizontal)
                }
            }
            .navigationTitle("Dog images")
        }
    }
}

Answer 1

@Published var uiImages = [UIImage]()

Red flag! The term [UIImage] is immediately suspect. Images (especially straight from photos) are big. An array of images is a great way to run out of memory.

You can keep an array of references to images, but not an array of actual images.