C# 代码错误，未将对象引用设置到对象的实例

Question

private void btnSend_Click(object sender, EventArgs e)
{
if (cbTimeSend.Checked)
{
tmSend.Enabled = true;
}
else
{
tmSend.Enabled = false;
}

        if (!sp1.IsOpen) //如果没打开
        {
            MessageBox.Show("请先打开串口！", "Error");
            return;
        }
       // string strSend = null;
        String strSend = txtSend.Text.ToString();

            if (radio1.Checked == true) //“HEX发送” 按钮 
            {
                //处理数字转换
                string sendBuf = strSend;
                string sendnoNull = sendBuf.Trim();
                string sendNOComma = sendnoNull.Replace(',', ' ');    //去掉英文逗号
                string sendNOComma1 = sendNOComma.Replace('，', ' '); //去掉中文逗号
                string strSendNoComma2 = sendNOComma1.Replace("0x", "");   //去掉0x
                strSendNoComma2.Replace("0X", "");   //去掉0X
                string[] strArray = strSendNoComma2.Split(' ');

                int byteBufferLength = strArray.Length;
                for (int i = 0; i < strArray.Length; i++)
                {
                    if (strArray[i] == "")
                    {
                        byteBufferLength--;
                    }
                }
                // int temp = 0;
                byte[] byteBuffer = new byte[byteBufferLength];
                int ii = 0;
                for (int i = 0; i < strArray.Length; i++)        //对获取的字符做相加运算
                {

                    Byte[] bytesOfStr = Encoding.Default.GetBytes(strArray[i]);

                    int decNum = 0;
                    if (strArray[i] == "")
                    {
                        //ii--;     //加上此句是错误的，下面的continue以延缓了一个ii，不与i同步
                        continue;
                    }
                    else
                    {
                        decNum = Convert.ToInt32(strArray[i], 16); //atrArray[i] == 12时，temp == 18 
                    }

                    try    //防止输错，使其只能输入一个字节的字符
                    {
                        byteBuffer[ii] = Convert.ToByte(decNum);
                    }
                    catch (System.Exception ex)
                    {
                        MessageBox.Show("字节越界，请逐个字节输入！", "Error");
                        tmSend.Enabled = false;
                        return;
                    }

                    ii++;
                }
                sp1.Write(byteBuffer, 0, byteBuffer.Length);
            }
            else        //以字符串形式发送时 
            {
                sp1.WriteLine(txtSend.Text);    //写入数据
            }

    }

void sp1_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
//输出当前时间
DateTime dt = DateTime.Now;
txtReceive.Text += dt.GetDateTimeFormats('f')[0].ToString() + "\r\n";
txtReceive.SelectAll();
txtReceive.SelectionColor = Color.Blue; //改变字体的颜色
try
{
byte[] receivedData = new byte[sp1.BytesToRead]; //创建接收字节数组
sp1.Read(receivedData, 0, receivedData.Length); //读取数据
if (receivedData.Length == 0)
return;
sp1.DiscardInBuffer(); //清空SerialPort控件的Buffer
if (receivedData.Length == 3 && receivedData[0] == 0xFF && receivedData[1] == _totalBytes[1] &&
receivedData[2] == 0x00)

            {
                //_totalBytes[1] = Convert.ToByte(_totalBytes[1] == 0xB5 ? 0xB6 : 0xB5);
                _totalBytes[1] = Convert.ToByte(_totalBytes[1] == 0xB6 ? 0xB5 : 0xB6);
                //_size += _totalBytes[1] == 0xB5 ? 512 : 0;
                _size += _totalBytes[1] == 0xB6 ? 512 : 0;
                SendBytes(false);
            }
            else
            {
                //发送失败
            }
            string strRcv = null;
            if (rdSendStr.Checked)
            {
                strRcv = sp1.Encoding.GetString(receivedData);
            }
            else
            {
                //int decNum = 0;//存储十进制
                for (int i = 0; i < receivedData.Length; i++) //窗体显示
                {

                    strRcv += receivedData[i].ToString("X2");  //16进制显示
                }
            }
            txtReceive.Text += strRcv + "\r\n";
        }
        catch (System.Exception ex)
        {
            MessageBox.Show(ex.Message, "出错提示");
            txtSend.Text = "";
        }
    }

 串口发送一段指定的字符串，串口接收，串口收到回复消息，提示出错。未将对象引用设置到对象的实例

Answer 1

判断条件改为：
if(treeView1.SelectedNode==null || treeView1.SelectedNode.Tag ==null)
{

//……
}
原因：
SelectedNode 有可能为空值