Question

我有一个执行HTTP请求并从网站检索数据的方法，它按预期工作，我正确获取了数据。我没办法做的就是在调用该方法时返回检索到的值。

这是代码...

func myFunction(zipCode: String)->String{
    var myData:String = ""

    let siteLink = "http://example.com/zip/" + zipCode
    let url = URL(string: siteLink)

    let task = URLSession.shared.dataTask(with: url!) { data, response, error in
        guard error == nil else {
            print(error!)
            return
        }
        guard let data = data else {
            print("Data is empty")
            return
        }
        let json = try! JSONSerialization.jsonObject(with: data, options: [])
        guard let jsonArray = json as? [[String: String]] else {
            return
        }
        myData = jsonArray[0]["MyPropertyName"]!
        // Here, myData outputs, "Info for zip code 52484 from HTTP request"
    }

    task.resume()

    return myData
}

当我调用myFunction时，我得到了一个空字符串...

myFunction(zipCode: "52484")// Outputs an empty string

我期望看到的是返回值"Info for zip code 52484 from HTTP request"，因为在返回调用之前myData内的let task =变量已被修改。我尝试在let task =内部返回，但这无法在Swift中完成。

调用myFunction时如何返回检索到的值？

Answer 1

您需要完成，因为请求是异步的

func myFunction(zipCode: String,completion:@escaping(_ str:String?) -> () ) {

    let siteLink = "http://example.com/zip/" + zipCode
    let url = URL(string: siteLink)

    let task = URLSession.shared.dataTask(with: url!) { data, response, error in
        guard error == nil else {
            print(error!)
            completion(nil)
            return
        }
        guard let data = data else {
            print("Data is empty")
            completion(nil)
            return
        }
        let json = try! JSONSerialization.jsonObject(with: data, options: [])
        guard let jsonArray = json as? [[String: String]] else {
            completion(nil)
            return
        }
        let myData = jsonArray[0]["MyPropertyName"]!
        completion(myData) 
    } 
    task.resume() 
}

致电

myFunction(zipCode: "52484") { (str) in 
  if let st = str {
    print(st)
   }
}

返回从HTTP请求中获取的值的方法

1 个答案: