从 '(_, _, _) throws -> ()' 类型的抛出函数到非抛出函数类型 '(URLResponse?, Data?, Error?) -> Void 的无效转换

Posted 2023-03-04

【中文标题】从 \'(_, _, _) throws -> ()\' 类型的抛出函数到非抛出函数类型 \'(URLResponse?, Data?, Error?) -> Void 的无效转换

【英文标题】：Invalid conversion from throwing function of type '(_, _, _) throws -> ()' to non-throwing function type '(URLResponse?, Data?, Error?) -> Void从 '(_, _, _) throws -> ()' 类型的抛出函数到非抛出函数类型 '(URLResponse?, Data?, Error?) -> Void 的无效转换

【发布时间】：2017-05-30 17:50:19

【问题描述】：

我正在尝试按照 Ray Wenderlich 网站上的教程学习使用 Instruments。示例代码是用 Swift 2 编写的，我相信在我被允许运行它之前，我必须将代码迁移到最新的 Swift 版本。我已经完成了转换错误的一半，但我对以下代码区域感到困惑：

class Flickr 

  let processingQueue = OperationQueue()

  func searchFlickrForTerm(_ searchTerm: String, completion : @escaping (_ results: FlickrSearchResults?, _ error : NSError?) -> Void)

    let searchURL = flickrSearchURLForSearchTerm(searchTerm)
    let searchRequest = URLRequest(url: searchURL)

    NSURLConnection.sendAsynchronousRequest(searchRequest, queue: processingQueue) response, data, error in
      if error != nil 
        completion(nil,error as! NSError)
        return
      

      var JSONError : NSError?


        let resultsDictionary = try JSONSerialization.jsonObject(with: data!, options: []) as? NSDictionary

      if JSONError != nil 
        completion(nil, JSONError)
        return
      

      switch (resultsDictionary!["stat"] as! String) 
      case "ok":
        print("Results processed OK")
      case "fail":
        let APIError = NSError(domain: "FlickrSearch", code: 0, userInfo: [NSLocalizedFailureReasonErrorKey:resultsDictionary!["message"]!])
        completion(results: nil, error: APIError)
        return
      default:
        let APIError = NSError(domain: "FlickrSearch", code: 0, userInfo: [NSLocalizedFailureReasonErrorKey:"Unknown API response"])
        completion(nil, APIError)
        return
      

      let photosContainer = resultsDictionary!["photos"] as! NSDictionary
      let photosReceived = photosContainer["photo"] as! [NSDictionary]

      let flickrPhotos : [FlickrPhoto] = photosReceived.map 
        photoDictionary in

        let photoID = photoDictionary["id"] as? String ?? ""
        let title = photoDictionary["title"] as? String ?? ""
        let farm = photoDictionary["farm"] as? Int ?? 0
        let server = photoDictionary["server"] as? String ?? ""
        let secret = photoDictionary["secret"] as? String ?? ""

        let flickrPhoto = FlickrPhoto(photoID: photoID, title: title, farm: farm, server: server, secret: secret)

        return flickrPhoto
      

      DispatchQueue.main.async(execute: 
        completion(FlickrSearchResults(searchTerm: searchTerm, searchResults: flickrPhotos), nil)
      )
    
  

  fileprivate func flickrSearchURLForSearchTerm(_ searchTerm:String) -> URL 
    let escapedTerm = searchTerm.addingPercentEscapes(using: String.Encoding.utf8)!
    let URLString = "https://api.flickr.com/services/rest/?method=flickr.photos.search&api_key=\(apiKey)&text=\(escapedTerm)&per_page=30&format=json&nojsoncallback=1"
    return URL(string: URLString)!
  

我收到以下代码行的错误：

NSURLConnection.sendAsynchronousRequest(searchRequest, queue: processingQueue) response, data, error in
      if error != nil 
        completion(nil,error as! NSError)
        return
      

我对如何使用 do、try、catch 进行修改感到有些困惑，因此我们将不胜感激任何帮助，以便我可以运行应用程序以使用 Instruments。

这里是教程的链接：https://www.raywenderlich.com/97886/instruments-tutorial-with-swift-getting-started

【问题讨论】：

问题是你有try 可以抛出错误，但你没有捕捉到它，所以它假设闭包因此需要允许抛出错误，它不会.只需do-catchtry在闭包中抛出的错误或使用try?，不会抛出错误。

【参考方案1】：

用这个替换你的 Flickr 类。

class Flickr 

  let processingQueue = OperationQueue()

  func searchFlickrForTerm(_ searchTerm: String, completion : @escaping (_ results: FlickrSearchResults?, _ error : NSError?) -> Void)

let searchURL = flickrSearchURLForSearchTerm(searchTerm)
let searchRequest = URLRequest(url: searchURL)

NSURLConnection.sendAsynchronousRequest(searchRequest, queue: processingQueue) response, data, error in
    guard let data = data, error == nil else 
        completion(nil, error as NSError?)
        return
    

    guard let jsonObject = try? JSONSerialization.jsonObject(with: data,
                                                                    options: JSONSerialization.ReadingOptions(rawValue: 0)),
    let resultsDictionary = jsonObject as? Dictionary<String, Any>
        else
    
        return
    


    switch (resultsDictionary["stat"] as! String) 
    case "ok":
        print("Results processed OK")
    case "fail":
        let APIError = NSError(domain: "FlickrSearch", code: 0, userInfo: [NSLocalizedFailureReasonErrorKey:resultsDictionary["message"]!])
        completion(nil, APIError)
        return
    default:
        let APIError = NSError(domain: "FlickrSearch", code: 0, userInfo: [NSLocalizedFailureReasonErrorKey:"Unknown API response"])
        completion(nil, APIError)
        return
    

    let photosContainer = resultsDictionary["photos"] as! NSDictionary
    let photosReceived = photosContainer["photo"] as! [NSDictionary]

    let flickrPhotos : [FlickrPhoto] = photosReceived.map 
        photoDictionary in

        let photoID = photoDictionary["id"] as? String ?? ""
        let title = photoDictionary["title"] as? String ?? ""
        let farm = photoDictionary["farm"] as? Int ?? 0
        let server = photoDictionary["server"] as? String ?? ""
        let secret = photoDictionary["secret"] as? String ?? ""

        let flickrPhoto = FlickrPhoto(photoID: photoID, title: title, farm: farm, server: server, secret: secret)

        return flickrPhoto
    

    DispatchQueue.main.async(execute: 
        completion(FlickrSearchResults(searchTerm: searchTerm, searchResults: flickrPhotos), nil)
    )

  

  fileprivate func flickrSearchURLForSearchTerm(_ searchTerm:String) -> URL 
let escapedTerm = searchTerm.addingPercentEscapes(using: String.Encoding.utf8)!
let URLString = "https://api.flickr.com/services/rest/?method=flickr.photos.search&api_key=\(apiKey)&text=\(escapedTerm)&per_page=30&format=json&nojsoncallback=1"
return URL(string: URLString)!
  

抱歉，间距都搞砸了，但问题是您没有正确处理错误。当您执行 JSONSerialization 时，它可能会抛出，因此您必须将其包装在 do catch 块中，或者您可以使用 !如果抛出错误，则忽略抛出和崩溃，或者？如果失败则返回 nil。