Unable to cast object of type 'System.Web.UI.LiteralControl'

Question

Unable to cast object of type 'System.Web.UI.LiteralControl' error on quantity,amount

protected void gdShoppingCart_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
bool result;

ShopingCartBLL cartObj = new ShopingCartBLL();

TextBox txtId = (TextBox)(gdShoppingCart.Rows[e.RowIndex].Cells[0].Controls[0]);
cartObj.BookId = Convert.ToInt32(txtId.Text);
TextBox txtTitle = (TextBox)(gdShoppingCart.Rows[e.RowIndex].Cells[1].Controls[0]);
cartObj.Title = txtTitle.Text;
TextBox txtPrice = (TextBox)(gdShoppingCart.Rows[e.RowIndex].Cells[2].Controls[0]);
cartObj.Price = Convert.ToDouble(txtPrice.Text);
TextBox txtQuantity = (TextBox)(gdShoppingCart.Rows[e.RowIndex].Cells[3].Controls[0]);
cartObj.Quantity =Convert.ToInt32(txtQuantity.Text);
TextBox txtAmount = (TextBox)(gdShoppingCart.Rows[e.RowIndex].Cells[4].Controls[0]);
cartObj.Amount = Convert.ToDouble(txtAmount.Text);
cartObj.UserId = 2;//replace it with session or pass url
result = cartObj.UpdateAnItem();

if (result)
{
string script = "<script>alert('UpDated')</script>";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "UpDated", script);
gdShoppingCart.EditIndex = -1;
BindData();
}
else
{
string script = "<script>alert('UpDated Failed')</script>";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "UpDated", script);
}

}
<Columns>
<asp:BoundField DataField="boo_id" HeaderText="ID" />
<asp:BoundField DataField="boo_title" HeaderText="Title" />
<asp:BoundField DataField="car_price" HeaderText="Price" />
<asp:TemplateField HeaderText="Quantity">
<EditItemTemplate>
<asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("car_quantity") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("car_quantity") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:Label ID="lblShipping" runat="server" Text="Shipping"></asp:Label>
<br />
<asp:Label ID="lblTotalAmount" runat="server" Text="Total Amount"></asp:Label>
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Amount">
<EditItemTemplate>
<asp:TextBox ID="TextBox2" runat="server" Text='<%# Bind("car_amount") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("car_amount") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:TextBox ID="txtShipping" runat="server"></asp:TextBox>
<br />
<asp:TextBox ID="txtTotalAmount" runat="server"></asp:TextBox>
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Edit" ShowHeader="False">
<EditItemTemplate>
<asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="True" CommandName="Update" Text="Update"></asp:LinkButton>
&nbsp;<asp:LinkButton ID="LinkButton2" runat="server" CausesValidation="False" CommandName="Cancel" Text="Cancel"></asp:LinkButton>
</EditItemTemplate>
<ItemTemplate>
<asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False" CommandName="Edit" Text="Edit"></asp:LinkButton>
</ItemTemplate>
<FooterTemplate>
<asp:Button ID="btnCheckOut" runat="server" Text="Checkout>>" />