generateThumbnailRepresentations

func generateThumbnailRepresentations() {
    
    // Set up the parameters of the request.
    guard let url = Bundle.main.url(forResource: "example", withExtension: "png") else {
        
        // Handle the error case.
        assert(false, "The URL can't be nil")
        return
    }
    let size: CGSize = CGSize(width: 60, height: 90)
    let scale = UIScreen.main.scale
    
    // Create the thumbnail request.
    let request = QLThumbnailGenerator.Request(fileAt: url,
                                               size: size,
                                               scale: scale,
                                               representationTypes: .all)
    
    // Retrieve the singleton instance of the thumbnail generator and generate the thumbnails.
    let generator = QLThumbnailGenerator.shared
    generator.generateRepresentations(for: request) { (thumbnail, type, error) in
        DispatchQueue.main.async {
            if thumbnail == nil || error != nil {
                // Handle the error case gracefully.
            } else {
                // Display the thumbnail that you created.
            }
        }
    }
}