GridCalculatedColumn error "operator * cannot be applied for string"

[Venkatesh]

Hi,
In my aspx page, i have the below columns:

<telerik:GridTemplateColumn DataField="OrderQuantity" HeaderText="Order Quantity"
                   UniqueName="OrderQuantity" Visible="true">
                   <InsertItemTemplate>
                       <telerik:RadTextBox ID="RadtxtOrderQuantity" runat="server" Text='<%# Bind("OrderQuantity") %>'>
                       </telerik:RadTextBox>
                   </InsertItemTemplate>
                   <EditItemTemplate>
                       <telerik:RadTextBox ID="RadtxtOrderQuantity" runat="server" Text='<%# Eval("OrderQuantity") %>'>
                       </telerik:RadTextBox>
                   </EditItemTemplate>
                   <ItemTemplate>
                       <telerik:RadTextBox ID="RadtxtOrderQuantity" ReadOnly="true" runat="server" Text='<%# Eval("OrderQuantity") %>' />
                   </ItemTemplate>
               </telerik:GridTemplateColumn>
               <telerik:GridTemplateColumn DataField="UnitPrice" HeaderText="Unit Price" UniqueName="UnitPrice"
                   Visible="true">
                   <InsertItemTemplate>
                       <telerik:RadNumericTextBox ID="RadtxtUnitPrice" runat="server" Text='<%# Bind("UnitPrice") %>'>
                       </telerik:RadNumericTextBox>
                   </InsertItemTemplate>
                   <EditItemTemplate>
                       <telerik:RadNumericTextBox ID="RadtxtUnitPrice" runat="server" Text='<%# Eval("UnitPrice") %>'>
                       </telerik:RadNumericTextBox>
                   </EditItemTemplate>
                   <ItemTemplate>
                       <telerik:RadNumericTextBox ID="RadtxtUnitPrice" Type="Currency" ReadOnly="true" runat="server"
                           Text='<%# Eval("UnitPrice") %>' />
                   </ItemTemplate>
               </telerik:GridTemplateColumn>
               <telerik:GridCalculatedColumn DataFormatString="{0:C}" DataType="System.Double" HeaderText="Extended Price"
                   UniqueName="ExtendedPrice" DataFields="OrderQuantity,UnitPrice" Expression="{0}*{1}"
                   FooterText="Total : " Aggregate="Sum">
               </telerik:GridCalculatedColumn>

When the page loads, i am binding the grid with empty datatable:

private DataTable CreateEmptyTable()
        {
            DataTable dt = new DataTable("PurchaseData");

            try
            {

                dt.Columns.Add(new DataColumn("OrderQuantity"));
                dt.Columns.Add(new DataColumn("UnitPrice"));
                dt.Columns.Add(new DataColumn("ExtendedPrice"));

                DataRow dr = dt.NewRow();

                dr["OrderQuantity"] = 0;
                dr["UnitPrice"] = 0;
                dr["ExtendedPrice"] = 0;
                dt.Rows.Add(dr);

            }
            catch (Exception)
            {

                throw;
            }
            return dt;
        }

bindgrid()
{
 radgrid1.DataSource = CreateEmptyTable();
 radgrid1.DataBind();
}

I am getting the error as "operator * cannot be applied between string and string".
The columns are integer type in sql.  How to to fix this?
Thanks

[Venkatesh]

HI,
Any help on this issue?

[Antonio Stoilkov]

Hello Venkatesh,

In order to resolve your issue you should specify the DataColumn objects its DataType property so the RadGrid knows what the column types are.

DataTable dt = new DataTable("PurchaseData");

try
{

    dt.Columns.Add(new DataColumn("OrderQuantity") { DataType = typeof(int) });
    dt.Columns.Add(new DataColumn("UnitPrice") { DataType = typeof(int) });
    dt.Columns.Add(new DataColumn("ExtendedPrice") { DataType = typeof(int) });

    DataRow dr = dt.NewRow();

    dr["OrderQuantity"] = 0;
    dr["UnitPrice"] = 0;
    dr["ExtendedPrice"] = 0;
    dt.Rows.Add(dr);

}
catch (Exception)
{

    throw;
}
return dt;

Regards,
Antonio Stoilkov
the Telerik team