Display value in Label while adding row in GridView using C# in ASP.Net

How to display quantity of each item into label at the time of adding in GridView.

I want to display quantity of item in label, which is in outside of GridView .

When i add item in GridView then that item quantity display in label (lbqty).

If same item exit in GridView then, adding item quantity get sum and display in label

<asp:TextBox ID="TextBox1" AutoPostBack="true" runat="server" Placeholder="Input Bale No"
    OnTextChanged="TextBox1_TextChanged" Height="16px" Width="100px" Style="margin-left: 0px"></asp:TextBox>
<asp:DropDownList ID="DropDownList1" runat="server" Enabled="false" Height="20px"
    Width="130px">
</asp:DropDownList>
<asp:TextBox ID="txtorderno" Placeholder="Order No" ReadOnly="true" runat="server"
    Height="16px" Width="38px"></asp:TextBox>
<asp:TextBox ID="txtqty" Placeholder="QTY" ReadOnly="true" runat="server" Height="16px"
    Width="21px"></asp:TextBox>
&nbsp;<asp:TextBox ID="txtpid" ReadOnly="true" runat="server" Height="19px" Width="55px"></asp:TextBox>
&nbsp;<asp:Button ID="Button1" runat="server" Text="Add" Visible="false" OnClick="Button1_Click"
    Height="26px" Width="35px" />
<asp:Label ID="Label1" runat="server" Text="." ForeColor="#CC0000"></asp:Label>
<asp:Label ID="lbgvck" runat="server" Text="." ForeColor="#CC0000"></asp:Label>
<asp:Label ID="lbpk" runat="server" Text="."></asp:Label>
<asp:Label ID="lbgv" runat="server" Text="."></asp:Label>
&nbsp; &nbsp;&nbsp; Order QTY :<strong><asp:Label ID="lbitqty" runat="server" Text="Label"></asp:Label>
</strong>&nbsp;Pack QTY : <strong>
    <asp:Label ID="lbitpqty" runat="server" Text="Label"></asp:Label>
    <asp:Label ID="lbitpqty0" runat="server" Text="Label"></asp:Label>
</strong></div>
<table class="auto-style1">
    <tr>
        <td>
            &nbsp;
        </td>
        <td>
            <asp:GridView ID="GridView1" runat="server" HeaderStyle-BackColor="#66ccff" HeaderStyle-ForeColor="White"
                CssClass="mygrdContent" PagerStyle-CssClass="pager" HeaderStyle-CssClass="header"
                RowStyle-CssClass="rows" AutoGenerateColumns="false" OnRowDeleting="GridView1_RowDeleting"
                OnRowEditing="GridView1_RowEditing" OnRowUpdating="GridView1_RowUpdating" AllowSorting="True"
                OnRowDataBound="GridView1_RowDataBound" ShowFooter="True">
                <Columns>
                    <asp:TemplateField HeaderText="Bale_No">
                        <ItemTemplate>
                            <asp:Label ID="Prdno" runat="server" Text='<%#Bind("Prdno")%>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Description">
                        <ItemTemplate>
                            <asp:Label ID="Descriptionitem" runat="server" Text='<%#Bind("Descriptionitem")%>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Orderno">
                        <ItemTemplate>
                            <asp:Label ID="Orderno" runat="server" Text='<%#Bind("Orderno")%>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="QTY">
                        <ItemTemplate>
                            <asp:Label ID="QTY" runat="server" Text='<%#Bind("QTY")%>'></asp:Label>
                        </ItemTemplate>
                        <FooterTemplate>
                            <asp:Label ID="lblTotal" runat="server"></asp:Label></FooterTemplate>
                    </asp:TemplateField>
                    <asp:CommandField ShowDeleteButton="True" ButtonType="Button" />
                </Columns>
                <HeaderStyle BackColor="#66CCFF" ForeColor="White"></HeaderStyle>
                <SelectedRowStyle BackColor="Yellow" />
            </asp:GridView>

if (DropDownList1.SelectedItem != null)
{
    // get value and text which item you have selected
    int codeitem = Convert.ToInt32(DropDownList1.SelectedItem.Value.ToString());
    string Descriptionitem = DropDownList1.SelectedItem.Text.ToString();


    //add the selected item to gridview

    DataTable dtgridview = ViewState["dt"] as DataTable;
    DataRow dr2 = dtgridview.NewRow();
    bool ifExist = false;
    foreach (DataRow dr in dtgridview.Rows)
    {
        if (dr["Prdno"].ToString() == TextBox1.Text.Trim())
        {
            ifExist = true;
            break;
        }

    }
    if (!ifExist)
    {
        dr2["Prdno"] = TextBox1.Text.Trim();
        dr2["Codeitem"] = codeitem;
        dr2["Descriptionitem"] = Descriptionitem;
        dr2["Orderno"] = txtorderno.Text;

        dr2["QTY"] = txtqty.Text;


        if (dtgridview.Rows.Count < Convert.ToInt16(DDLPktype.SelectedItem.Value))
        {
            dtgridview.Rows.Add(dr2);
        }
        else
        {
            ClientScript.RegisterClientScriptBlock(this.GetType(), "", "alert('You can not insert more than " + dtgridview.Rows.Count + " rows')", true);
        }


        // dtgridview.Rows.Add(dr2);
        ViewState["dt"] = dtgridview;
        GridView1.DataSource = dtgridview;
        GridView1.DataBind();
    }
    else
    {
        // this.lbgvck.Visible = true;
        lbgv.Text = "Bale Already Added...";
    }

    clear();
}