小编典典

NSURLConnection sendAsynchronousRequest不能从封闭中获取变量

swift

我正在尝试使用POST从PHP页面获得简单的文本响应。我有以下代码:

func post(url: String, info: String) -> String {
    var URL: NSURL = NSURL(string: url)!
    var request:NSMutableURLRequest = NSMutableURLRequest(URL:URL)
    var output = "Nothing Returned";
    request.HTTPMethod = "POST";
    var bodyData = info;
    request.HTTPBody = bodyData.dataUsingEncoding(NSUTF8StringEncoding);

    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()){

        response, data, error in

        output = (NSString(data: data, encoding: NSUTF8StringEncoding))!


    }

    return output
}

虽然这段代码不会引发任何错误,但是当我这样调用它时:

println(post(url, info: data))

即使我更改了该行,它也只会打印:“什么也没返回”:

output = (NSString(data: data, encoding: NSUTF8StringEncoding))!

对此:

println((NSString(data: data, encoding: NSUTF8StringEncoding)))

它确实打印出正确的响应。我的变量在这里做错了吗?


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2020-07-07

共1个答案

小编典典

这是在调用使用完成处理程序块/关闭的异步函数。因此,您需要在自己的代码中使用完成处理程序模式。这包括将方法的返回类型更改为,Void并添加一个新的completionHandler闭包,该闭包将在异步调用完成后被调用:

func post(url: String, info: String, completionHandler: (NSString?, NSError?) -> ()) {
    let URL = NSURL(string: url)!
    let request = NSMutableURLRequest(URL:URL)
    request.HTTPMethod = "POST"
    let bodyData = info
    request.HTTPBody = bodyData.dataUsingEncoding(NSUTF8StringEncoding);

    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) { response, data, error in
        guard data != nil else {
            completionHandler(nil, error)
            return
        }

        completionHandler(NSString(data: data!, encoding: NSUTF8StringEncoding), nil)
    }
}

或者,由于NSURLConnection现在已正式弃用,因此最好使用NSURLSession

func post(url: String, info: String, completionHandler: (NSString?, NSError?) -> ()) -> NSURLSessionTask {
    let URL = NSURL(string: url)!
    let request = NSMutableURLRequest(URL:URL)
    request.HTTPMethod = "POST"
    let bodyData = info
    request.HTTPBody = bodyData.dataUsingEncoding(NSUTF8StringEncoding);

    let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
        dispatch_async(dispatch_get_main_queue()) {
            guard data != nil else {
                completionHandler(nil, error)
                return
            }

            completionHandler(NSString(data: data!, encoding: NSUTF8StringEncoding), nil)
        }
    }
    task.resume()

    return task
}

您这样称呼它:

post(url, info: info) { responseString, error in
    guard responseString != nil else {
        print(error)
        return
    }

    // use responseString here
}

// but don't try to use response string here ... the above closure will be called
// asynchronously (i.e. later)

注意,为简单起见,我采用了尾随闭包语法(请参见Swift编程语言:Closures的
尾随闭包
部分),但希望它能说明这一思想:您不能立即返回异步方法的结果,因此请提供一个完成处理程序关闭,将在异步方法完成后调用。

2020-07-07