文本框自动生成代码不起作用

Question

我正在开发我的asp.net项目，我正在尝试为自动生成代码制作ASP.net文本框，但它无法正常工作，示例自动生成代码= ID1。

我尝试使用这部分，

string txt = txtBatchNo.Text;
txtBatchNo.Text = "C" + Convert.ToInt32(txt.Substring(1, txt.Length - 1)) + 1;

代码：

protected void btnAdd_Click(object sender, EventArgs e)
{
    int newId = 1;

    if (selectGRNDetailId == -1)
    {
        {
            try
            {
                if (dtFabricItem.Rows.Count > 0)
                {
                    newId = Convert.ToInt32(dtFabricItem.Rows[dtFabricItem.Rows.Count - 1]["GRNDetailsID"].ToString()) + 1;
                }
            }
            catch (Exception)
            {
                newId = 1;
            }
        }
    }
    else
    {
        newId = selectGRNDetailId;
    }

    if (dtFabricItem == null)
    {
        CreateFabricDetails();
        dtFabricItem = dt;
    }
    else
    {
        CreateFabricDetails();
    }

    DataRow dr2 = null;
    dr2 = dt.NewRow();
    dr2["GRNDetailsID"] = newId;
    dr2["GRNDetailID"] = selectGRNId;
    dr2["BatchNO"] = txtBatchNo.Text;
    dr2["ItemId"] = Convert.ToInt32(ddlYarnName.SelectedValue);
    dr2["ItemName"] = ddlYarnName.SelectedItem.Text;
    dr2["LotId"] = Convert.ToInt32(ddlLotNo.SelectedValue);
    dr2["LotName"] = ddlLotNo.SelectedItem.Text;

    dr2["FibetLot"] = txtFiberLot.Text;

    dr2["ContainsNo"] = txtContainsNO.Text;

    dr2["Shade"] = txtShade.Text;
    dr2["Quantity"] = Convert.ToDecimal(txtQty.Text).ToString();
    dr2["YarnPrice"] = Convert.ToDecimal(txtYarnPrice.Text).ToString();
    dr2["Cornweight"] = Convert.ToDecimal(txtCornWeight.Text).ToString();
    dr2["BoxWeight"] = Convert.ToDecimal(txtBoxWeight.Text).ToString();
    dr2["NumberofCones"] = Convert.ToDecimal(txtNumberofcones.Text).ToString();
    dr2["Numberofboxes"] = Convert.ToDecimal(txtNumberofboxes.Text).ToString();

    dt.Rows.Add(dr2);
    //txtNumberofcones.Text = (Convert.ToDecimal(txtBoxWeight.Text) / Convert.ToDecimal(txtCornWeight.Text)).ToString();

    if (dtFabricItem == null || dtFabricItem.Rows.Count == 0)
    {
        dtFabricItem = dt;
        dtFabricItem.PrimaryKey = new DataColumn[] { dtFabricItem.Columns["GRNDetailsID"] };
    }
    else
    {
        dtFabricItem.PrimaryKey = new DataColumn[] { dtFabricItem.Columns["GRNDetailsID"] };
        dtFabricItem.Merge(dt);
    }

    //dtFabricItem.PrimaryKey = new DataColumn[] { dtFabricItem.Columns["GRNDetailsID"] };

    dtFabricItem.AcceptChanges();
    gvrItemDetails.DataSource = dtFabricItem;
    gvrItemDetails.DataBind();

    selectGRNDetailId = -1;
    ClearDetails();
}

TextBox Id = `txtBatchNo`