c# - 使用 Invoke 时跨线程操作无效

Question

我做了一个聊天系统，但出现了这个错误:

Cross-thread operation not valid: 'MessageBox' etc.

我所做的:我添加了一个调用。这是代码:

Invoke(new Action(() => messageBox.Items.Add(usersName.Text + ": " + receivedMessage)));

问题是，它基本上从其他用户发送了一条空白的消息。这是因为我在本地连接到聊天。这是一张图片:

接收消息:

private void MessageCallBack(IAsyncResult aResult)
{
    try
    {
        byte[] receivedData = new byte[1500];
        receivedData = (byte[])aResult.AsyncState;
        ASCIIEncoding aEncoding = new ASCIIEncoding();
        string receivedMessage = aEncoding.GetString(receivedData);
        Invoke(new Action(() => messageBox.Items.Add(usersName.Text + ": " + receivedMessage)));
        buffer = new byte[1500];
        socket.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref theirIp, new AsyncCallback(MessageCallBack), buffer);
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

发送消息:

private void sendBtn_Click(object sender, EventArgs e)
{
    try
    {
        if (messageTb.Text == "")
        {
            return;
        }
        else
        {
            ASCIIEncoding eEncoding = new ASCIIEncoding();
            byte[] msg = new byte[1500];
            msg = eEncoding.GetBytes(messageTb.Text);
            socket.Send(msg);
            messageBox.Items.Add(yourName.Text + ": " + messageTb.Text);
            messageTb.Clear();
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
    this.ActiveControl = messageTb;
}

Answer 1

每当您尝试访问窗体主线程以外的其他线程中的控件时，就会发生此异常。

我使用的是下面的简单日志机制，这个只适合简单的应用。

private delegate void LogDelegate(ListBox messageBox, string data);

private LogDelegate _logDelegate;
private void Log(ListBox messageBox, string data)
{
    if (messageBox.InvokeRequired)
    {
        LogDelegate logDelegate = Log;
        Invoke(logDelegate, messageBox, data);
    }
    else
    {
        messageBox.Items.Add(data);
    }
}

public Form1()
{
    InitializeComponent();
    //don't forget, initialize the delegate
    _logDelegate = Log;
}

private void btn_Start_Click(object sender, EventArgs e)
{
    Log("Anything to log");
}
private void MessageCallBack(IAsyncResult aResult)
{
    try
    {
        //Instead of Invoke use 
        //Invoke(new Action(() => messageBox.Items.Add(usersName.Text + ": " + receivedMessage)));
        Log("Anything to log");

    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

正如我所说，代码可以在任何地方使用并且很简单。但对于更复杂的日志记录机制和更好的性能，请使用 Log4Net 或 NLog。