SerialPort正在线程上使用它自己的Eventloop。当您订阅DataReceived事件时，最好不要在UI线程上阅读端口的数据。您最好将其保留在后台线程上，并在获得所有数据后切换上下文。
我要做的另一个补充是在窗体关闭时调用port.Close。在可以释放SerialPort示例之后。
以下方法已被更改，以包括我上面描述的更改：

// the delegate now takes a string argument, holding the received data
public delegate void UpdateText(string text);

// checks for the correct EventType and calls updateText 
// after all available data is read
private void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{
    try
    {
        if (e.EventType == SerialData.Chars)
        {
            // read all data and then handle
            updateTextBox(port.ReadExisting());
        }
        else
        {
            port.Close();
        }
    }
    catch
    {
        port.Close();
    }     
}

// called twice, once from the background thread
// and by BeginInvoke
public void updateTextBox(string text)
{
    // do we need to be switch to the UI thread?
    if (tWGT.InvokeRequired)
    {
        // yes, so setup the delegate and pass on the parameter
        // notice how BeginInvoke will call this same method again
        tWGT.BeginInvoke(new UpdateText(updateTextBox), text);
    }
    else
    {
        // show the received data
        tWGT.AppendText(text);
        tWGT.ScrollToCaret();
    } 
}

// nicely close
private void Form1_FormClosed(object sender, FormClosedEventArgs e)
{
    // if omitted you'll run into problems if this forms gets reopened
    if (port.IsOpen) port.Close();
    port.Dispose();
}