ios - 后台异步来自 JSON 的 Realm

Question

我想在后台异步地从 JSON 编写 Realm，但我不明白为什么我的代码不能正常工作。

override func viewDidLoad() {
    super.viewDidLoad()

    myFunc()

}

和 myFunc():

func myFunc() {

        let realm = try! Realm()

        // get file JSON from local device and write data from it to RealmDB
        if realm.isEmpty {

            //local file JSON
            let file = Bundle.main.path(forResource: "file", ofType: "json")!
            let url = URL(fileURLWithPath: file)
            let jsonData = NSData(contentsOf: url)!

            //Serialization JSON
            let json = try! JSONSerialization.jsonObject(with: jsonData as Data, options: [])


            DispatchQueue.main.async {

            realm.beginWrite()

            //Create data from JSON to our objects
            realm.create(DataRoot.self, value: json, update: true)

            try! realm.commitWrite()

            }
        }
    }

DB 正在创建，但下一步(如我所见)出错:

  override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        return (transport.filter("id == 1").first?.routes.count)!
    }

所以，我想在后台等待完全写入数据库(例如，显示进度 View )然后进行下一步。

Answer 1

您必须检查 numberOfRows 方法中的可选值并像这样执行

    func myFunc() {
        let queue1 = DispatchQueue(label: "com.appname.queue")
        queue1.async {
            let realm = try! Realm()
            // get file JSON from local device and write data from it to RealmDB
            if realm.isEmpty {

                //local file JSON
                let file = Bundle.main.path(forResource: "file", ofType: "json")!
                let url = URL(fileURLWithPath: file)
                let jsonData = NSData(contentsOf: url)!

                //Serialization JSON
                let json = try! JSONSerialization.jsonObject(with: jsonData as Data, options: [])
                realm.beginWrite()

                //Create data from JSON to our objects
                realm.create(DataRoot.self, value: json, update: true)

                try! realm.commitWrite()

                DispatchQueue.main.async {

                    self.tableview.reloadData()

                }

            }
        }
    }


    override func tableView(_ tableView: UITableView,     numberOfRowsInSection section: Int) -> Int {
        if let routes = transport.filter("id == 1").first?.routes {
            return routes.count
        } 
            return 0
    }