ASP.NET Dynamically Adding a Gridview - asp.net

Question

I have a gridview as such
<asp:GridView runat="server" ID="gvShoppingCart" AutoGenerateColumns="false" EmptyDataText="There is nothing in your shopping cart." AlternatingRowStyle-CssClass="tr_dark" HeaderStyle-CssClass="header_req" BorderWidth="0px" GridLines="None" AllowPaging="true" PageSize="25" AllowSorting="false" Width="100%" ShowFooter="true" DataKeyNames="ProductId" OnRowDataBound="gvShoppingCart_RowDataBound" OnRowCommand="gvShoppingCart_RowCommand">
<Columns>
<asp:TemplateField HeaderText="Product Name" SortExpression="productName" HeaderStyle-CssClass="product" >
<ItemTemplate>
<asp:Label ID="ProductNameField" runat="server" Text='<%# Eval("description").ToString() %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<Columns>
<asp:TemplateField HeaderText="Pack Size" SortExpression="packSize" HeaderStyle-CssClass="packsize" >
<ItemTemplate>
<asp:Label ID="PackSizeField" runat="server" Text='<%# Eval("packSize").ToString()%>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<Columns>
<asp:TemplateField HeaderText="Stock" SortExpression="address" HeaderStyle-CssClass="stock">
<ItemTemplate>
<asp:Label ID="StockField" runat="server" Text='<%# DisplayStockLevel(Eval("StockIndicator").ToString()) %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<Columns>
<asp:TemplateField HeaderText="Quantity" HeaderStyle-CssClass="quantity" >
<ItemTemplate>
<asp:TextBox runat="server" Width="30" ID="txtQuantity" Text='<%# Eval("Quantity") %>'></asp:TextBox>
<asp:TextBox runat="server" Visible="false" Width="30" ID="txtProductCode" Text='<%# Eval("ProductCode") %>'></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<Columns>
<asp:TemplateField HeaderText="Actual Price" HeaderStyle-CssClass="actual" SortExpression="address">
<ItemTemplate>
<asp:Label ID="TradePriceField" runat="server" Text='<%# DisplayMoney(Eval("UnitPrice").ToString())%>'></asp:Label>
<asp:Label ID="TradePriceFieldHidden" runat="server" Text='<%# Eval("UnitPrice").ToString()%>' Visible="false"></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<Columns>
<asp:BoundField DataField="TotalPrice" HeaderText="Total" HeaderStyle-CssClass="total" HeaderStyle-HorizontalAlign="Right" DataFormatString="{0:C}" />
</Columns>
<Columns>
<asp:TemplateField HeaderText="" HeaderStyle-CssClass="remove">
<ItemTemplate>
<asp:ImageButton ImageUrl="~/img/icons/cross.gif" width="10" height="10" alt="Cancel" runat="server" ID="btnRemove" CommandName="Remove" CommandArgument='<%# Eval("ProductId") %>'/>
</ItemTemplate>
</asp:TemplateField>
</Columns>
And now trying to add a footer rows dynamically ( because I need multiple footer rows)
Protected Sub gvShoppingCart_RowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs) Handles gvShoppingCart.RowDataBound
' If we are binding the footer row, let's add in our total
If e.Row.RowType = DataControlRowType.Footer Then
e.Row.Cells(5).Text = "<strong>Total Cost:</strong>"
e.Row.Cells(6).Text = ShoppingCart.Instance.GetSubTotal().ToString("C")
End If
Dim grid As GridView = CType(sender, GridView)
''gets the current footer row to clone
Dim footer As GridViewRow = grid.FooterRow
Dim numCells = footer.Cells.Count
Dim newRow As New GridViewRow(footer.RowIndex + 1, -1, footer.RowType, footer.RowState)
''have to add in the right number of cells
''this also copies any styles over from the original footer
For i As Integer = 0 To numCells - 1
Dim emptyCell As New TableCell
emptyCell.ApplyStyle(grid.Columns(i).ItemStyle)
newRow.Cells.Add(emptyCell)
Next
newRow.Cells(5).Text = "Total Discount:"
newRow.Cells(6).Text = "55.00"
''add new row to the gridview table, at the very bottom
CType(grid.Controls(0), Table).Rows.Add(newRow)
End Sub
But getting the error
Object reference not set to an instance of an object.
Dim numCells = footer.Cells.Count
Any idea whats going wrong ?

Answer 1

The GridView FooterRow property is only set after the RowDataBound method has been called. You can access it in the DataBound method of the GridView.
Protected Sub gvShoppingCart_DataBound(ByVal sender As Object, ByVal e As EventArgs)
Dim footerRow as GridViewRow = gvShoppingCart.FooterRow
End Sub

Answer 2

First of all your GridView Markup is incorrect. Define Columns just once like this.
<asp:GridView ID="gvShoppingCart" runat="server"
AlternatingRowStyle-CssClass="tr_dark"
AllowPaging="true"
AllowSorting="false"
AutoGenerateColumns="false"
BorderWidth="0px"
DataKeyNames="ProductId"
EmptyDataText="There is nothing in your shopping cart."
GridLines="None"
HeaderStyle-CssClass="header_req"
PageSize="25"
ShowFooter="true"
Width="100%"
OnRowCommand="gvShoppingCart_RowCommand"
OnRowDataBound="gvShoppingCart_RowDataBound">
<Columns>
<asp:TemplateField HeaderText="Product Name" SortExpression="productName" HeaderStyle-CssClass="product">
<ItemTemplate>
<asp:Label ID="ProductNameField" runat="server"
Text='<%# Eval("description").ToString() %>'>
</asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Pack Size" SortExpression="packSize" HeaderStyle-CssClass="packsize">
<ItemTemplate>
<asp:Label ID="PackSizeField" runat="server"
Text='<%# Eval("packSize").ToString()%>'>
</asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Stock" SortExpression="address" HeaderStyle-CssClass="stock">
<ItemTemplate>
<asp:Label ID="StockField" runat="server"
Text='<%# DisplayStockLevel(Eval("StockIndicator").ToString()) %>'>
</asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Quantity" HeaderStyle-CssClass="quantity">
<ItemTemplate>
<asp:TextBox ID="txtQuantity" runat="server"
Width="30"
Text='<%# Eval("Quantity") %>'>
</asp:TextBox>
<asp:TextBox ID="txtProductCode" runat="server"
Visible="false"
Width="30"
Text='<%# Eval("ProductCode") %>'>
</asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Actual Price" HeaderStyle-CssClass="actual" SortExpression="address">
<ItemTemplate>
<asp:Label ID="TradePriceField" runat="server"
Text='<%# DisplayMoney(Eval("UnitPrice").ToString())%>'>
</asp:Label>
<asp:Label ID="TradePriceFieldHidden" runat="server"
Text='<%# Eval("UnitPrice").ToString()%>'
Visible="false">
</asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="TotalPrice" HeaderText="Total"
HeaderStyle-CssClass="total" HeaderStyle-HorizontalAlign="Right"
DataFormatString="{0:C}" />
<asp:TemplateField HeaderText="" HeaderStyle-CssClass="remove">
<ItemTemplate>
<asp:ImageButton ID="btnRemove" runat="server"
ImageUrl="~/img/icons/cross.gif"
Width="10"
Height="10"
AlternateText="Cancel"
CommandName="Remove"
CommandArgument='<%# Eval("ProductId") %>' />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
Secondly, you are getting error because you have not defined your FooterTemplate anywhere.