Provider.swift

struct Provider: TimelineProvider {
    private let quoteManager = QuoteManager()
    [...]
    func getSnapshot(in context: Context, completion: @escaping (QuoteEntry) -> ()) {
        if context.isPreview {
            let quote = Quote(quote: "Roses are red", author: "Nobody knows")
            completion(QuoteEntry(date: Date(), quote: quote))
       } else {
            let quote = quoteManager.getSingleQuote()
            completion(QuoteEntry(date: Date(), quote: quote))
       }
    }
}