Question

在快速编码期间，我想从我的函数中获取值，但出现了错误，它显示错误：

错误：使用未解析的标识符＆＃39;金额

获得＆＃34;数量＆＃34;的正确方法是什么？从这个功能？

func UserAmountGET() -> Int{
    let url = NSURL(string: myIP + "users/amount")
    let request = NSMutableURLRequest(url: url! as URL)
    request.httpMethod = "GET"

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

        guard let _:NSData = data as NSData?, let _:URLResponse = response, error == nil else{
            print("error")
            return
        }

        let json = JSON(data: data!)
        let amount = Int(json["data"][0]["username"].stringValue)!
    }

    task.resume()
    return amount  // Error: Use of unresolved Identifier 'amount'
}

Answer 1

问题是amount变量在网络请求的闭包范围内，无法从函数主体访问。据推测，您的网络请求可能需要一些时间才能完成，因此您可以使用在网络请求返回时运行的闭包。

func UserAmountGET(completion: @escaping (Int) -> ()) {
    let url = NSURL(string: myIP + "users/amount")
    let request = NSMutableURLRequest(url: url! as URL)
    request.httpMethod = "GET"

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

        guard let _:NSData = data as NSData?, let _:URLResponse = response, error == nil else{
            print("error")
            return
        }

        let json = JSON(data: data!)
        let amount = Int(json["data"][0]["username"].stringValue)!

        completion(amount)

    }
    task.resume()

}

然后你会这样称呼你的方法：

UserAmountGET(completion: { amount in

    // use the `amount` value here

})

对于网络请求等异步回调，这种闭包的使用更为自然。

价值回归有问题

1 个答案: