从类型 (_,_,_) throws -> Void 到非抛出函数类型 (NSData?, NSURLResponse?, NSError?) -> Void 的无效转换

Question

我已经写了这段代码：

func getjson() {
        let urlPath = "https://api.whitehouse.gov/v1/petitions.json?limit=100"
        let url = NSURL(string: urlPath)
        let session = NSURLSession.sharedSession()
        let task = session.dataTaskWithURL(url!, completionHandler: {data, response, error -> Void in
            print("Task completed")
            if(error != nil) {
                print(error!.localizedDescription)
            }
            let err: NSError?
            if let jsonResult = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as? NSDictionary {
                if(err != nil) {
                    print("JSON Error \(err!.localizedDescription)")
                }
                if let results: NSArray = jsonResult["results"] as? NSArray {
                    dispatch_async(dispatch_get_main_queue(), {
                        self.tableData = results
                        self.Indextableview.reloadData()
                    })
                }
            }
        })

        task.resume()

    }

更新到 XCode 7 后，它给了我这个错误：从 (_, _, _) 类型的抛出函数抛出的无效转换 -> Void 到非抛出函数类型 (NSData?, NSURLResponse?, NSError?) - > 无效。排队了，让任务在哪里。

谢谢

Answer 1

您需要按如下方式实现 Do Try Catch 错误处理：

import UIKit
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true

extension URL {
    func asyncDownload(completion: @escaping (_ data: Data?, _ response: URLResponse?, _ error: Error?) -> ()) {
        URLSession.shared
            .dataTask(with: self, completionHandler: completion)
            .resume()
    }
}

---

let jsonURL = URL(string: "https://api.whitehouse.gov/v1/petitions.json?limit=100")!
let start = Date()
jsonURL.asyncDownload { data, response, error in

    print("Download ended:", Date().description(with: .current))
    print("Elapsed Time:", Date().timeIntervalSince(start), terminator: " seconds\n")
    print("Data size:", data?.count ?? "nil", terminator: " bytes\n\n")

    guard let data = data else {
        print("URLSession dataTask error:", error ?? "nil")
        return
    }

    do {
        let jsonObject = try JSONSerialization.jsonObject(with: data)
        if let dictionary = jsonObject as? [String: Any],
            let results = dictionary["results"] as? [[String: Any]] {
            DispatchQueue.main.async {
                results.forEach { print($0["body"] ?? "", terminator: "\n\n") }
      //        self.tableData = results
      //        self.Indextableview.reloadData()
            }
        }
    } catch {
        print("JSONSerialization error:", error)
    }
}
print("\nDownload started:", start.description(with: .current))

Answer 2

正如 Leo 所建议的，您的问题是您使用的是 try，但不在 do-try-catch 构造中，这意味着它推断出闭包被定义为抛出错误，但由于它没有这样定义，你会得到那个错误。

所以，添加do-try-catch:

func getjson() {
    let urlPath = "https://api.whitehouse.gov/v1/petitions.json?limit=100"
    let url = URL(string: urlPath)!
    let session = URLSession.shared
    let task = session.dataTask(with: url) { data, response, error in
        print("Task completed")

        guard let data = data, error == nil else {
            print(error?.localizedDescription)
            return
        }

        do {
            if let jsonResult = try JSONSerialization.jsonObject(with: data) as? [String: Any] {
                if let results = jsonResult["results"] as? [Any] {
                    DispatchQueue.main.async {
                        self.tableData = results
                        self.indexTableView.reloadData()
                    }
                }
            }
        } catch let parseError {
            print("JSON Error \(parseError.localizedDescription)")
        }
    }

    task.resume()
}

Answer 3

在 Swift 2 中，将所有 NSError 替换为 ErrorType

试试这个。

  class func fetchWeatherForLocation(locationCode: String = "", shouldShowHUD: Bool = false, completionHandler: (data: NSDictionary?, error: ErrorType?) -> ()) {



    let url = NSURL(string: "myurl")               
    let task =  NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in

        if let dataWithKey = data {

            do {
                let jsonForDataWithTemprature = try NSJSONSerialization.JSONObjectWithData(dataWithKey, options:NSJSONReadingOptions.MutableContainers)

                guard let arrayForDataWithKey :NSArray = jsonForDataWithTemprature as? NSArray else {
                    print("Not a Dictionary")
                    return
                }

                let dictionaryWithTemprature = arrayForDataWithKey.firstObject as! NSDictionary

                completionHandler(data: dictionaryWithTemprature, error: nil)

            }
            catch let JSONError as ErrorType {
                print("\(JSONError)")
            }

        }
    }

    task.resume()
}

Answer 4

更改代码 try-catch 中的错误类型对我有用。

"将所有 NSError 替换为 ErrorType"