C#：使用 Winforms 关闭 SerialPort 的正确方法

Question

I have an app where I read from the serialport, everything goes fine, until I close the app. When I click on the [X] the app simply hangs, the UI: unresponsive.

I read from the port in the DataReceived event handler, and I close the port when FormClosed happens:

    private void MainForm_FormClosed(object sender, FormClosedEventArgs e)
    {
        mySerialPort.Close();
    }

Answer 1

It's not a bug.

The only reason it would hang when you close it is because in the event handler of your SerialPort object, you're synchronizing a call with the main thread (typically by calling invoke). SerialPort's close method waits for its EventLoopRunner thread which fires DataReceived/Error/PinChanged events to terminate, but since your own code in the event is also waiting for main thread to respond, you run into a dead lock situation.

The reason the bug report was closed 'as designed' is because the 'bug' is in your own code.

Answer 2

Serial Port hangs while closing

This is a known issue with the SerialPort class and described in this Product Feedback article as well as several threads in these forums. You may notice the "closed by design" dismissal.

Answer 3

If your application is calling Invoke to process recevied data try calling BeginInvoke instead.

Instead of:

this.Invoke(d, new object[] { s, tb });

use:

this.BeginInvoke(d, new object[] { s, tb });

Answer 4

Simplest solution if you only want to close the port when the app closes, is to just not bother to Close() the port. The port will still get closed anyway when the app disposes of the serial port. The port will be available to be opened again by your app when it restarts, or by other apps that may wish to use the port.

Answer 5

this work very good :

 private void Form_FormClosing(object sender, FormClosingEventArgs e)
    {

        if (_serialPort.IsOpen)
        {
            e.Cancel = true; //cancel the fom closing
            Thread CloseDown = new Thread(new ThreadStart(CloseSerialOnExit)); //close port in new thread to avoid hang
            CloseDown.Start(); //close port in new thread to avoid hang
        }
    }

 private void CloseSerialOnExit()
    {
        try
        {
            _serialPort.Close(); //close the serial port
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message); //catch any serial port closing error messages
        }
        this.Invoke(new EventHandler(NowClose)); //now close back in the main thread
    }

    private void NowClose(object sender, EventArgs e)
    {
        this.Close(); //now close the form
    }