如何从远程保护程序下载 json 文件并保存到bundle以供离线访问

Question

每次打开应用程序时，我都可以从服务器下载一个json文件并将其放入TableView中。（见下面的代码）

但是，我还想允许使用上次下载的文件进行离线访问。所以基本上我在弄清楚如何保存下载的文件以供离线本地访问时遇到了麻烦。任何帮助（特别是例子）非常感谢。

 class KalkanTableController: UITableViewController {
var TableData:Array< String > = Array < String >()

override func viewDidLoad() {
super.viewDidLoad()

get_data_from_url("http://ftp.MY FILE LOCATION/kalkanInfoTest.json")
    if let path = Bundle.main.path(forResource: "kalkanInfoTest", ofType: "json") {
        do {
            let jsonData = try NSData(contentsOfFile: path, options: NSData.ReadingOptions.mappedIfSafe)
            do {
                let jsonResult: NSDictionary = try JSONSerialization.jsonObject(with: jsonData as Data, options: JSONSerialization.ReadingOptions.mutableContainers) as! NSDictionary
            } catch {}
        } catch {}
    }
}

override func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return TableData.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
    cell.textLabel?.text = TableData[indexPath.row]
    return cell
}
func get_data_from_url(_ link:String)
{
    let url:URL = URL(string: link)!
    let session = URLSession.shared
    let request = NSMutableURLRequest(url: url)
    request.httpMethod = "GET"
    request.cachePolicy = URLRequest.CachePolicy.reloadIgnoringCacheData

    let task = session.dataTask(with: request as URLRequest, completionHandler: {
        (
        data, response, error) in
        guard let _:Data = data, let _:URLResponse = response  , error == nil else {
           return
        }
        self.extract_json(data!)
    }) 
    task.resume()
}

func extract_json(_ data: Data)
{
    let json: Any?
    do
    {
        json = try JSONSerialization.jsonObject(with: data, options: [])
    }
    catch
    {
        return
    }
    guard let data_list = json as? NSArray else
    {
        return
    }
    if let item_list = json as? NSArray
    {
        for i in 0 ..< data_list.count
        {
            if let item_obj = item_list[i] as? NSDictionary
            {
                if let item_name = item_obj["kalkanInfo"] as? Stri                          
                    {
                         TableData.append(item_name)
                         print(item_name)
                }
            }
        }
    }
    DispatchQueue.main.async(execute: {self.do_table_refresh()})
}
func do_table_refresh()
{
    DispatchQueue.main.async(execute: {
        self.tableView.reloadData()
        return
    })
}

}

Answer 1

您可以尝试使用以下方法在本地保存 json 以保存在磁盘上

override func viewDidLoad() {
    super.viewDidLoad()
    if readKalkanDataFromDisk() {
        extract_json(readKalkanDataFromDisk())
    } else {
        get_data_from_url("http://ftp.MY FILE LOCATION/kalkanInfoTest.json")
    }
}
func get_data_from_url(_ link:String)
{
    let url:URL = URL(string: link)!
    let session = URLSession.shared
    let request = NSMutableURLRequest(url: url)
    request.httpMethod = "GET"
    request.cachePolicy = URLRequest.CachePolicy.reloadIgnoringCacheData

    let task = session.dataTask(with: request as URLRequest, completionHandler: {
        (
        data, response, error) in
        guard let _:Data = data, let _:URLResponse = response  , error == nil else {
            return
        }
        saveKalkanDataOnDisk(kalkanData: data!)
        self.extract_json(data!)
    }) 
    task.resume()
}
func saveKalkanDataOnDisk(kalkanData: Data) {
    do {
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
        let fileURL = documentsURL.appendingPathComponent("Kalkan.json")
        try kalkanData.write(to: fileURL, options: .atomic)
    } catch { }
}
func readKalkanDataFromDisk() -> Data? {
    let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
    let filePath = documentsURL.appendingPathComponent("Kalkan.json").path
    if FileManager.default.fileExists(atPath: filePath), let data = FileManager.default.contents(atPath: filePath) {
        return data
    }
    return nil
}