Question

我正在尝试从外部JSON文件中获取一个字符串，该文件位于Web服务器上，并且它成功获取它，但它在一个闭包中，它获取了值，我需要将它放到外面所以我可以用变量returnip返回它我该怎么做？

func getJsonFromUrl() -> String {

    let URL2 = "https://url.com/asd.php";
    let url = URL(string: URL2)
    URLSession.shared.dataTask(with:url!) { (data, response, error) in
        if error != nil {
            print(error as Any)
        } else {
            do {

                let parsedData = try JSONSerialization.jsonObject(with: data!) as! [String:Any]
                let ips = parsedData["ip"] as! String
                print("The IP is: " + ips) //Prints the value correctly
               var returnip = ips //The value that I want to return, that does not go outside this closure
            } catch let error as NSError {
                print(error)
            }
        }

        }.resume()
     return returnip //Does not return anything
}

由于

Answer 1

您无法从异步函数返回，并且闭包内的return语句仅从闭包本身返回。

您需要使用完成处理程序。此外，在解析网络响应时，请勿使用强制解包选项/强制转换选项。

func getJsonFromUrl(name: String, completion: @escaping (String?)->()) {
    //use name variable just as you would in a normal function
    let URL2 = "https://url.com/asd.php"
    let url = URL(string: URL2)
    URLSession.shared.dataTask(with:url!) { (data, response, error) in
        if error != nil {
            print(error as Any)
            completion(nil)
        } else {
            do {
                guard let parsedData = try JSONSerialization.jsonObject(with: data!) as? [String:Any] else { completion(nil); return }
                guard let ips = parsedData["ip"] as? String else {completion(nil); return }
                print("The IP is: " + ips) //Prints the value correctly
                completion(ips)
            } catch let error as NSError {
                print(error)
                completion(nil)
            }
        }
    }.resume()
}

然后你可以这样称呼它：

getJsonFromUrl(name: "Input", completion: { ips in
    print(ips)
    //you can only use the value inside the closure of completion
})

在闭包内指定的返回变量 - Swift

1 个答案: