在Swift中从web调用获取值[重复]

Question

我试图从Swift中的PHP脚本中获得返回的值。然而，我似乎不断地得到错误：

var value: String!

func run(idNumber: Int) {
    let request = NSMutableURLRequest(url: URL(string: "https://mywebsite.com/file.php")!)
    request.httpMethod = "POST"
    let postString = "a=Hello"
    request.httpBody = postString.data(using: String.Encoding.utf8)

    let task = URLSession.shared.dataTask(with: request as URLRequest) {
        data, response, error in

        if error != nil {
            //answer = error;
        }

        let answerString = String(data: data!, encoding: String.Encoding.utf8)
        self.value = answerString
    }
    task.resume()
}

func getValue() -> String{
    return value
}

当调用getvalue()函数时会发生错误。然而，当我一创建“answerString”就打印出来时，它就成功地打印出来了！

在这里调用函数：

let access = ApiAccess()
access.run(idNumber: 0)
print(access.getValue())

Answer 1

发出请求是一项异步任务。在调用getvalue之前，需要等待闭包回调被调用。

可以向run方法添加闭包回调。这样，您将知道请求何时完成，并可以打印结果：

var value: String!

func run(idNumber: Int, @escaping callback: () -> Void) {

    let request = NSMutableURLRequest(url: URL(string: "https://mywebsite.com/file.php")!)
    request.httpMethod = "POST"
    let postString = "a=Hello"
    request.httpBody = postString.data(using: String.Encoding.utf8)

    let task = URLSession.shared.dataTask(with: request as URLRequest) {
        data, response, error in

        if error != nil {
            //answer = error;
        }


        let answerString = String(data: data!, encoding: String.Encoding.utf8)
        self.value = answerString
        callback()

    }
    task.resume()

}

func getValue() -> String{
    return value
}

let access = ApiAccess()
access.run(idNumber: 0) {
   print(access.getValue())
}