Question

您好我尝试更改标签元素，但文字没有变化。

       public partial class Form1 : Form
        {       
            public Form1()
            {
                InitializeComponent();
            }

           private void button1_Click(object sender, EventArgs e)
            {
                sendPOST("http://example");            
            }

            public static void sendPOST(string URL)
            {
                // Create a request using a URL that can receive a post. 
                HttpWebRequest request = (HttpWebRequest) WebRequest.Create(URL);
                // Set the ContentType property of the WebRequest.
                request.ContentType = "application/x-www-form-urlencoded";

                // Set the Method property of the request to POST.
                request.Method = "POST";

                // start the asynchronous operation
                request.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback),request);

                allDone.WaitOne();        
            }

private static void GetRequestStreamCallback(IAsyncResult asynchronousResult)
        {

            HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

            // End the operation
            Stream postStream = request.EndGetRequestStream(asynchronousResult);

            // Convert the string into a byte array.
            byte[] byteArray = Encoding.UTF8.GetBytes("");

            // Write to the request stream.
            postStream.Write(byteArray, 0, postData.Length);
            postStream.Close();

            // Start the asynchronous operation to get the response
            request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
        }

    private static void GetResponseCallback(IAsyncResult asynchronousResult)
           {
              //.....
              Form1 test = new Form1();
              test.statusLabel.Text  = responseString; //dont write anything

               Console.WriteLine(responseString); //works well
              //.....
        }

如何更改？

更新：添加更多代码。如何获取现有的Form1实例以更新Form1 LabelField以在asyn完成后显示某些内容？

Answer 1

根据问题的评论，我猜你可以这样做：将你想要更改的表单实例作为用户定义的对象state传递给导致GetResponseCallback被调用的调用（大多数{ {1}}方法允许您传递用户定义的对象，然后在BeginXYZ中。然后你可以做这样的事情：

IAsyncResult.State

请注意，由于多线程问题，您可能无法更改Form1 test = asynchronousResult.State as Form1; test.StatusLabel.Text = responseString;属性，因此必须使用Text这样做。 SO上有许多线索可以描述这一点。

我现在没有正常工作的代码示例，但如果我没弄错的话，它应该是这样的：

Control.Invoke

在静态void GetResponseCallback中更改表单标签

1 个答案: