未提供预期参数

我在数据库中opbal1了一个表，其中包含字段sno, voc, date, ledcode, type, amt ,part。
直到我保存数据为止，还可以，但是当我编辑数据时出现错误

The parameterized query '(@voc nvarchar(11),@date nvarchar(10),@ledcode nvarchar(4000),@t'
expects the parameter '@ledcode', which was not supplied

我的代码：

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        FirstGrid();
    }
}
private void FirstGrid()
{
    string sno = Request.QueryString["sno"];
    Response.Write(sno);
    if (sno == null)
    {
        DataTable dt = new DataTable();
        DataRow dr = null;
        dt.Columns.Add(new DataColumn("0", typeof(string)));
        dt.Columns.Add(new DataColumn("1", typeof(string)));
        dt.Columns.Add(new DataColumn("2", typeof(string)));
        dt.Columns.Add(new DataColumn("3", typeof(string)));
        dt.Columns.Add(new DataColumn("4", typeof(string)));
        dt.Columns.Add(new DataColumn("5", typeof(string)));
        dt.Columns.Add(new DataColumn("6", typeof(string)));
        dt.Columns.Add(new DataColumn("7", typeof(string)));
        dr = dt.NewRow();
        dr[0] = string.Empty;
        dr[1] = string.Empty;
        dr[2] = string.Empty;
        dr[3] = string.Empty;
        dr[4] = string.Empty;
        dr[5] = string.Empty;
        dr[6] = string.Empty;
        dr[7] = string.Empty;
        dt.Rows.Add(dr);
        ViewState["CurrentTable"] = dt;
        grvOpbal.DataSource = dt;
        grvOpbal.DataBind();
    }
    else
    {
        Response.Write(Session["flag"]);
        if (Session["flag"] == "2" || Session["flag"] == "3")
        {
            conn.Open();
            hdnFlag.Value = Session["flag"].ToString();
            btnSave.Enabled = true;
            SqlCommand cmd = new SqlCommand("select * from opbal1 where sno=@sno", conn);
            SqlDataAdapter da = new SqlDataAdapter();
            da.SelectCommand = cmd;
            cmd.Parameters.AddWithValue("@sno", sno);
            DataTable dt = new DataTable();
            da.Fill(dt);
            grvOpbal.DataSource = dt;
            ViewState["CurrentTable"] = dt;
            grvOpbal.DataBind();
            int i = 0;
            foreach (DataRow row in dt.Rows)
            {
                Label lblSno = (Label)grvOpbal.Rows[i].Cells[0].FindControl("lblSno");
                Label lblSrNumber = (Label)grvOpbal.Rows[i].Cells[1].FindControl("lblSrNumber");
                DropDownList ddlLedCode = (DropDownList)grvOpbal.Rows[i].Cells[2].FindControl("ddlLedCode");
                TextBox txtType = (TextBox)grvOpbal.Rows[i].Cells[3].FindControl("txtType");
                TextBox txtAmt = (TextBox)grvOpbal.Rows[i].Cells[4].FindControl("txtAmt");
                TextBox txtPart = (TextBox)grvOpbal.Rows[i].Cells[5].FindControl("txtPart");
                TextBox txtVoc = (TextBox)grvOpbal.Rows[i].Cells[6].FindControl("txtVoc");
                TextBox txtDate = (TextBox)grvOpbal.Rows[i].Cells[7].FindControl("txtDate");
                lblSrNumber.Text = Convert.ToInt32(i + 1).ToString();
                lblSno.Text = row[0].ToString();
                txtVoc.Text = row[1].ToString();
                txtDate.Text = row[2].ToString();
                ddlLedCode.SelectedValue = row[3].ToString();
                txtType.Text = row[4].ToString();
                if (txtType.Text == "D" || txtType.Text == "d")
                {
                    txtAmt.BackColor = System.Drawing.Color.Red;
                }
                else
                {
                    txtAmt.BackColor = System.Drawing.Color.Blue;
                }
                txtAmt.Text = row[5].ToString();
                txtPart.Text = row[6].ToString();
                i++;
            }
        }
    }
}
private void SetRowData()
{
    int rowIndex = 0;
    if (ViewState["CurrentTable"] != null)
    {
        DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
        DataRow drCurrentRow = null;
        if (dtCurrentTable.Rows.Count > 0)
        {
            for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
            {
                Label lblSno = (Label)grvOpbal.Rows[rowIndex].Cells[1].FindControl("lblSno");
                Label lblSrNumber = (Label)grvOpbal.Rows[rowIndex].Cells[2].FindControl("lblSrNumber");
                DropDownList ddlLedCode = (DropDownList)grvOpbal.Rows[rowIndex].Cells[3].FindControl("ddlLedCode");
                TextBox txtType = (TextBox)grvOpbal.Rows[rowIndex].Cells[4].FindControl("txtType");
                TextBox txtAmt = (TextBox)grvOpbal.Rows[rowIndex].Cells[5].FindControl("txtAmt");
                TextBox txtPart = (TextBox)grvOpbal.Rows[rowIndex].Cells[6].FindControl("txtPart");
                TextBox txtVoc = (TextBox)grvOpbal.Rows[rowIndex].Cells[7].FindControl("txtVoc");
                TextBox txtDate = (TextBox)grvOpbal.Rows[rowIndex].Cells[8].FindControl("txtDate");
                if (txtType.Text == "D")
                {
                    //txtType.Attributes.Add("OnFocus", "return OnFocus()");
                    txtAmt.BackColor = System.Drawing.Color.Red;
                }
                else
                {
                    txtAmt.BackColor = System.Drawing.Color.Blue;
                }
                drCurrentRow = dtCurrentTable.NewRow();
                dtCurrentTable.Rows[i - 1][0] = lblSno.Text;
                dtCurrentTable.Rows[i - 1][1] = txtVoc.Text;
                dtCurrentTable.Rows[i - 1][2] = txtDate.Text;
                dtCurrentTable.Rows[i - 1][3] = ddlLedCode.SelectedValue;
                dtCurrentTable.Rows[i - 1][4] = txtType.Text;
                dtCurrentTable.Rows[i - 1][5] = txtAmt.Text;
                dtCurrentTable.Rows[i - 1][6] = txtPart.Text;
                // dtCurrentTable.Rows[i - 1][7] = 
                lblSrNumber.Text = i.ToString();
                rowIndex++;
            }
            ViewState["CurrentTable"] = dtCurrentTable;
        }
    }
    else
    {
        Response.Write("Viewstate is null");
    }
}
protected void btnSave_Click(object sender, EventArgs e)
{
    SetRowData();
    conn.Open();
    DataTable table = ViewState["CurrentTable"] as DataTable;
    if (table != null)
    {
        foreach (DataRow row in table.Rows)
        {
            int j = 1;
            string lblSno = row.ItemArray[0] as string;
            string txtVoc = row.ItemArray[1] as string;
            string txtDate = row.ItemArray[2] as string;
            //string lblSrNumber = row.ItemArray[1] as string;
            string ddlLedCode = row.ItemArray[3] as string;
            string txtType = row.ItemArray[4] as string;
            string txtAmt = row.ItemArray[5] as string;
            string txtPart = row.ItemArray[6] as string;
            string lblSrNumber = j.ToString();
            j++;
            if (hdnFlag.Value == "1")
            {
                string sql1="insert into opbal1 values(@voc,@date,@ledcode,@type,@amt,@part)";
                SqlCommand cmd2 = new SqlCommand(sql1, conn);
                cmd2.Parameters.AddWithValue("@voc", mmvoc);
                cmd2.Parameters.AddWithValue("@date", today);
                cmd2.Parameters.AddWithValue("@ledcode", ddlLedCode);
                cmd2.Parameters.AddWithValue("@type", txtType);
                cmd2.Parameters.AddWithValue("@amt", txtAmt);
                cmd2.Parameters.AddWithValue("@part", "opbal");
                cmd2.ExecuteNonQuery();
            }
            else if (hdnFlag.Value == "2")
            {
                string today = DateTime.Now.ToString("yyyy-dd-M");    
                string sql = "update opbal1 set voc=@voc,date=@date,";
                sql += "ledcode=@ledcode,type=@type,amt=@amt,part=@part where sno=@sno";
                SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.Parameters.AddWithValue("@voc", txtVoc);
                cmd.Parameters.AddWithValue("@date", today);
                cmd.Parameters.AddWithValue("@ledcode", ddlLedCode);
                cmd.Parameters.AddWithValue("@type", txtType);
                cmd.Parameters.AddWithValue("@amt",txtAmt);
                cmd.Parameters.AddWithValue("@part", "opbal");
                cmd.Parameters.AddWithValue("@sno", lblSno);
                cmd.ExecuteNonQuery();
                btnSave.Enabled = false;
            }
        }
    }
}

if(ddlLedCode != null)
   cmd.Parameters.AddWithValue("@ledcode", ddlLedCode);
else
   cmd.Parameters.AddWithValue("@ledcode", DBNull.Value);

if (ddlLedCode != null)
     cmd.Parameters.Add("@ledcode", SqlDbType.NVarChar).Value = ddlLedCode;
else
     cmd.Parameters.Add("@ledcode", SqlDbType.NVarChar).Value = DBNull.Value;

foreach (DataRow row in table.Rows)
                {
                    int j = 1;
                    string lblSno = row[0].ToString();
                    string txtVoc = row[1].ToString();
                    string txtDate = row[2].ToString();
                    //string lblSrNumber = row.ItemArray[1] as string;
                    string ddlLedCode = row[3].ToString();
                    string txtType = row[4].ToString();
                    string txtAmt = row[5].ToString();
                    string txtPart = row[6].ToString();
}