Compare ASP.Net GridView TextBox values on Button Click using C#

Hi suhaas121,

You have to use GridViewRow FindControl method. Refer the updated code. 

HTML

<asp:GridView ID="Gridorder" OnRowDataBound="Gridorder_RowDataBound" CssClass="table table-responsive"
    AutoGenerateColumns="False" DataKeyNames="Id" runat="server" CellPadding="4" ForeColor="#333333" GridLines="None">
    <EditRowStyle BackColor="#999999" />
    <FooterStyle BackColor="#5D7B9D" ForeColor="White" Font-Bold="True" />
    <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <PagerStyle ForeColor="White" HorizontalAlign="Center" BackColor="#284775" />
    <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
    <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
    <SortedAscendingCellStyle BackColor="#E9E7E2" />
    <SortedAscendingHeaderStyle BackColor="#506C8C" />
    <SortedDescendingCellStyle BackColor="#FFFDF8" />
    <SortedDescendingHeaderStyle BackColor="#6F8DAE" />
    <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
    <Columns>
        <asp:TemplateField HeaderText="Select All">
            <HeaderTemplate>
                <asp:CheckBox ID="chkAll" runat="server" AutoPostBack="true" OnCheckedChanged="OnCheckedChanged" />
            </HeaderTemplate>
            <ItemTemplate>
                <asp:CheckBox ID="chkSelect" runat="server" AutoPostBack="true" OnCheckedChanged="OnCheckedChanged" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="ID" Visible="false">
            <ItemTemplate>
                <asp:Label ID="lblid" runat="server" Text='<%#Eval("Id") %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Part Number">
            <ItemTemplate>
                <asp:Label ID="lblpart" runat="server" Text='<%#Eval("Part_number") %>'></asp:Label>
                <asp:TextBox ID="txtpart" runat="server" Text='<%#Eval("Part_number") %>' Visible="false" Enabled="false"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Nomenclature">
            <ItemTemplate>
                <asp:Label ID="lblnom" runat="server" Text='<%#Eval("Nomenclature") %>'></asp:Label>
                <asp:TextBox ID="txtnom" runat="server" Text='<%#Eval("Nomenclature") %>' Visible="false" Enabled="false"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Vendor Code">
            <ItemTemplate>
                <asp:Label ID="lblven" runat="server" Text='<%#Eval("Vendor_Code") %>'></asp:Label>
                <asp:TextBox ID="txtven" runat="server" Text='<%#Eval("Vendor_Code") %>' Visible="false" Enabled="false"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Quantity">
            <ItemTemplate>
                <asp:Label ID="lblqu" runat="server" Text='<%#Eval("quantity") %>'></asp:Label>
                <asp:TextBox ID="txtqu" runat="server" Text='<%#Eval("quantity") %>' Visible="false"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Quantity Available">
            <ItemTemplate>
                <asp:Label ID="lblqua" runat="server" Text='<%#Eval("quantity_available") %>'></asp:Label>
                <asp:TextBox ID="txtqua" runat="server" Text='<%#Eval("quantity_available") %>' Visible="false" Enabled="false"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Unit Price">
            <ItemTemplate>
                <asp:Label ID="lblunt" runat="server" Text='<%#Eval("unit_price") %>'></asp:Label>
                <asp:TextBox ID="txtunt" runat="server" Text='<%#Eval("unit_price") %>' Visible="false" Enabled="false"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<br />
<asp:Button ID="btnUpdate" OnClick="btnupdate_Click" Visible="false" runat="server" Text="Button" />

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        if (Session["vendor"] != null)
        {
            GetGridviewData();
        }
    }
}

public void GetGridviewData()
{
    string[] vendors = Session["vendor"].ToString().Split('\n');
    foreach (string vendor in vendors)
    {
        var data = vendor.Trim();
        SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["connString"].ConnectionString);
        SqlCommand cmd = new SqlCommand("select Id,[Part_number],Nomenclature,[Vendor_Code],quantity,[quantity_available],[unit_price] from Catalouge where [Vendor_Code]=('" + data + "')", conn);
        Gridorder.DataSource = this.ExecuteQuery(cmd, "SELECT");
        Gridorder.DataBind();
    }
}

private DataTable ExecuteQuery(SqlCommand cmd, string action)
{
    string conString = (ConfigurationManager.ConnectionStrings["connString"].ConnectionString);
    using (SqlConnection con = new SqlConnection(conString))
    {
        cmd.Connection = con;
        switch (action)
        {
            case "SELECT":
                using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
                {
                    sda.SelectCommand = cmd;
                    using (DataTable dt = new DataTable())
                    {
                        sda.Fill(dt);
                        return dt;
                    }

                }
            case "UPDATE":
                con.Open();
                cmd.ExecuteNonQuery();
                con.Close();
                break;
        }
        return null;
    }
}

protected void OnCheckedChanged(object sender, EventArgs e)
{
    bool isUpdateVisible = false;
    CheckBox chk = (sender as CheckBox);
    if (chk.ID == "chkAll")
    {
        foreach (GridViewRow row in Gridorder.Rows)
        {
            if (row.RowType == DataControlRowType.DataRow)
            {
                row.Cells[0].Controls.OfType<CheckBox>().FirstOrDefault().Checked = chk.Checked;
            }
        }
    }
    CheckBox chkAll = (Gridorder.HeaderRow.FindControl("chkAll") as CheckBox);
    chkAll.Checked = true;
    foreach (GridViewRow row in Gridorder.Rows)
    {
        if (row.RowType == DataControlRowType.DataRow)
        {
            bool isChecked = row.Cells[0].Controls.OfType<CheckBox>().FirstOrDefault().Checked;
            for (int i = 1; i < row.Cells.Count; i++)
            {
                row.Cells[i].Controls.OfType<Label>().FirstOrDefault().Visible = !isChecked;
                if (row.Cells[i].Controls.OfType<TextBox>().ToList().Count > 0)
                {
                    row.Cells[i].Controls.OfType<TextBox>().FirstOrDefault().Visible = isChecked;
                }
                if (isChecked && !isUpdateVisible)
                {
                    isUpdateVisible = true;
                }
                if (!isChecked)
                {
                    chkAll.Checked = false;
                }
            }
        }
    }
    btnUpdate.Visible = isUpdateVisible;
}

protected void btnupdate_Click(object sender, EventArgs e)
{
    foreach (GridViewRow row in Gridorder.Rows)
    {
        int quan = Convert.ToInt32((row.FindControl("txtqu") as TextBox).Text.Trim());
        int avail = Convert.ToInt32((row.FindControl("txtqua") as TextBox).Text.Trim());
        if (quan > avail)
        {
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Quantity is greater than Available Quantity');window.location ='order.aspx';", true);
        }
        else
        {
            bool isChecked = (row.FindControl("chkSelect") as CheckBox).Checked;
            if (isChecked)
            {
                SqlCommand cmd = new SqlCommand("update Catalouge set quantity=@quantity where Id=@Id ");
                cmd.Parameters.AddWithValue("@quantity", quan);
                cmd.Parameters.AddWithValue("@Id", Gridorder.DataKeys[row.RowIndex].Value);
                this.ExecuteQuery(cmd, "SELECT");
            }
            btnUpdate.Visible = false;
            GetGridviewData();
        }
    }
}