请问COM关不掉第，关闭串口再次连接时提示COM占用访问失败，我不是已经CLOSE掉了吗，请问是哪里有问题吗

Question

private void button3_Click(object sender, EventArgs e)
{
SerialPort sp = new SerialPort();

        if (button3.Text == "连接串口")
        {
            
            if (comboBox1.SelectedIndex != -1 &&
           comboBox2.SelectedIndex != -1 &&
           comboBox3.SelectedIndex != -1 &&
           comboBox4.SelectedIndex != -1 &&
           comboBox5.SelectedIndex != -1)
            {
                try
                {
                    
                    sp.PortName = comboBox1.SelectedItem.ToString();
                    sp.BaudRate = Convert.ToInt32(comboBox2.SelectedItem);
                    sp.DataBits = Convert.ToInt32(comboBox5.SelectedItem);
                    #region

                    switch (comboBox3.SelectedItem.ToString())
                    {
                        case "None":
                            sp.Parity = Parity.None;
                            break;
                        case "奇校验":
                            sp.Parity = Parity.Odd;
                            break;
                        case "偶校验":
                            sp.Parity = Parity.Even;
                            break;
                    }
                    switch (comboBox4.SelectedItem.ToString())
                    {
                        case "0":
                            sp.StopBits = StopBits.None;
                            break;
                        case "1":
                            sp.StopBits = StopBits.One;
                            break;
                        case "1.5":
                            sp.StopBits = StopBits.OnePointFive;
                            break;
                        case "2":
                            sp.StopBits = StopBits.Two;
                            break;
                    }
                    sp.Open();
                    button3.Text = "关闭串口";
                    MessageBox.Show("连接成功");
                    #endregion

                }
                catch (Exception ex)
                {
                    MessageBox.Show("打开串口失败：" + ex.ToString());
                }
            }
            else
            {
                MessageBox.Show("连接失败,请选择正确的端口");
            }
        }
        else
        {
            sp.Close();
            button3.Text = "连接串口";
        }

Answer 1

当你点击关闭串口时，你这个点击事件先实例化了一个SerialPort类的对象，然后把它关闭了，然后把button文本变成了连接串口，就这样，而你之前最开始点击连接串口创建的SerialPort对象还在占用着COM口，你并没有把它关闭，所以当你再次点击时会提示被占用