swift – 如何从嵌套函数中更改变量？

参见英文答案 > AlamoFire GET api request not working as expected????????????????????????????????????1个
在嵌套函数范围内更改变量时,一旦保留范围,它就不会保持更改状态.在我的示例代码中,当我将变量xmlString设置为等于响应时,它正确地设置为响应.但是然后返回一个空字符串.
func getXmlString(url：String) – >字符串{
????????var xmlString：String =“”
????????Alamofire.request(.GET,url)
????????????.validate()
????????????.responseString {回复于
????????????????xmlString = response.result.value！
????????}
????????return xmlString
????}
我知道我遗失了一件小事,任何帮助更好地理解我的情况都会帮助我.谢谢

func getXmlString(url: String,completion: (xmlString: String) -> ()) {
            var xmlString: String = ""
            Alamofire.request(.GET,url)
                .validate()
                .responseString { response in
                    xmlString = response.result.value!

                 completion(xmlString)
             }
}

getXmlString(url: String){ xmlString in

//do something with your String
}