我的 Swift 应用出现错误，但我不知道如何修复它？你能帮助我吗？

Question

你好我的应用程序致命错误：在隐式展开可选值错误时意外发现 nil。我了解到选项有问题。但是我自己不知道怎么改，你能帮帮我吗？

ref = db.products(category: category.id)这是报错的地方

import UIKit
import FirebaseFirestore

class ProductsVC: UIViewController, ProductCellDelegate {

    // Outlets
    @IBOutlet weak var tableView: UITableView!
    
    // Variables
    var products = [Product]()
    var category: Category!
    var listener: ListenerRegistration!
    var db : Firestore!
    var showFavorites = false
    
    override func viewDidLoad() {
        super.viewDidLoad()
        db = Firestore.firestore()
        tableView.delegate = self
        tableView.dataSource = self
        tableView.register(UINib(nibName: Identifiers.ProductCell, bundle: nil), forCellReuseIdentifier: Identifiers.ProductCell)
        
        setupQuery()
    }
    
    func setupQuery() {
        
        var ref: Query!
        if showFavorites {
            ref = db.collection("users").document(UserService.user.id).collection("favorites")
        } else {
            ref = db.products(category: category.id)
               
        }
        
        listener = ref.addSnapshotListener({ (snap, error) in
            if let error = error {
                debugPrint(error.localizedDescription)
            }
            
            snap?.documentChanges.forEach({ (change) in
                let data = change.document.data()
                let product = Product.init(data: data)
                
                switch change.type {
                case .added:
                    self.onDocumentAdded(change: change, product: product)
                case .modified:
                    self.onDocumentModified(change: change, product: product)
                case .removed:
                    self.onDocumentRemoved(change: change)
                }
            })
        })
    }

Answer 1

要修复 id 的解包问题：

if let value = ref {
 value = db.products(category: category.id)
}