在 C# Form 应用程序中使用 BackGroundWorker 更新 UI 线程

Question

我有一个耗时的任务来测试几个网络连接。在下面的示例中，我将其限制为一个连接。 通常连接会很快返回，但可能会发生无法建立连接的情况，从而导致套接字超时。在此期间，我想在表单中显示一个“闲置”gif，当连接成功时，应用程序应该将表单中的图像更改为一些 绿色检查图标或在连接失败的情况下应显示红色图标“停止器”。

不知何故，我无法让闲置 gif 变得可见和动画。要模拟失败的连接，可以输入无效的端口号或不存在的地址。

任何线索我错过了什么或做错了什么？

    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        ///         
     #region BackgroundWorker

        private System.ComponentModel.BackgroundWorker backgroundWorker = new System.ComponentModel.BackgroundWorker();
        private delegate void SomeLongRunningMethodHandler(object sender, EventArgs e);

     #endregion
        private System.ComponentModel.IContainer components = null;

        Button button,button2;
        static Socket socket;
        static bool success;
        private static bool done;
        private Label lbl1;
        private Label lbl2;
        private TextBox address;
        private TextBox port;
        private PictureBox p;
        private static String port_number,host;


        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        private void RunTest(object o,EventArgs e)
        {
            p.Visible = true;
            SomeLongRunningMethodHandler synchronousFunctionHandler =
                default(SomeLongRunningMethodHandler);
            synchronousFunctionHandler = 
                TestConnection;
            synchronousFunctionHandler.Invoke(o, e);
        }

        private void TestConnection(object o, EventArgs e)
        {
            host = address.Text;
            port_number = port.Text;
           if (null != socket)
            {
                socket.Close();
            }

             Thread.Sleep(1000);
             IPEndPoint myEndpoint = new IPEndPoint(0, 0);


            IPHostEntry remoteMachineInfo = Dns.GetHostEntry(host);
            IPEndPoint serverEndpoint = new IPEndPoint(remoteMachineInfo.AddressList[0],
                int.Parse(port_number));



            socket = new Socket(myEndpoint.Address.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
            try
            {
                socket.Connect(serverEndpoint);
                success = true;
                p.Image = global::BlockingUI.Properties.Resources.accept;
            }
            catch
            {
                success = false;
                p.Image = global::BlockingUI.Properties.Resources.stopper;
            }
            done = true;
        }  


        private void ExitApp(object o, EventArgs e)
        {
            Application.Exit();
        }

    }

Answer 1

嗯，我是用自己的线程完成的。通常，您使用长时间运行的任务运行线程，并在需要时调用 Control.Invoke() 并使用指向将在 UI 上操作的函数的委托。看起来您正在使用后台工作线程更改 UI，这是不允许的。

此外，在 Winforms 中需要调用 Control.Invalidate() 来强制重新绘制 UI 并显示新图标。

Answer 2

如果你真的想使用BackgroundWorker，这个（或接近它的东西）应该为你指明正确的方向。您正在创建一个 BackgroundWorker 对象，但随后什么也不做。 BackgroundWorker 对象不允许访问 UI 元素，因为它们归 UI 线程所有，但是您可以传递 UI 值，就像我在这里使用 Tuple 所做的那样（如果您可以创建自己的类来保存这些值也想要），然后在工作人员完成后从 UI 线程修改 UI。

private struct ConnectionProperties
{
    public string Address;
    public string Port;
}

private void RunTest(object o, EventArgs e)
{
    BackgroundWorker worker = new System.ComponentModel.BackgroundWorker();

    worker.RunWorkerCompleted += TestComplete;
    worker.DoWork += TestConnection;

    p.Visible = true;

    //worker.RunWorkerAsync(new Tuple<string, string>(address.Text, port.Text));
    worker.RunWorkerAsync(new ConnectionProperties{ Address = address.Text, Port = port.Text });
}

private void TestConnection(object sender, DoWorkEventArgs e)
{
    bool success = false;
    //var connection = e.Argument as Tuple<string, string>;
    var connection = (ConnectionProperties)e.Argument;

    if (null != socket)
    {
        socket.Close();
    }

    Thread.Sleep(1000);

    IPEndPoint myEndpoint = new IPEndPoint(0, 0);
    IPHostEntry remoteMachineInfo = Dns.GetHostEntry(connection.Address);
    IPEndPoint serverEndpoint = new IPEndPoint(remoteMachineInfo.AddressList[0],
      int.Parse(connection.Port));

    socket = new Socket(myEndpoint.Address.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

    try
    {
        socket.Connect(serverEndpoint);
        success = true;
    }
    catch
    {
        success = false;
    }

    e.Result = success;
}

// Define other methods and classes here
private void TestComplete(object sender, RunWorkerCompletedEventArgs e)
{
    if (e.Error == null)
    {
        var success = (bool)e.Result;
        if (success)
        {
            p.Image = global::BlockingUI.Properties.Resources.accept;
        }
        else
        {
            p.Image = global::BlockingUI.Properties.Resources.stopper;
        }
    }
    else
    {
        //unexpected error, show message or whatever
    }
}