There are times when you need to ensure numeric values are entered into a TextBox control.
This can be accomplished using a CompareValidator with the Operator attribute set to "DataTypeCheck" and Type attribute set to the numeric type (Double or Integer).
The sample below allows only double values in the TextBox control.
<asp:TextBox ID="Mileage" runat="server" Columns="8"></asp:TextBox> ... <asp:CompareValidator ControlToValidate="Mileage" Operator="DataTypeCheck" ID="MileageValidator" runat="server" Type="Double" Display="Dynamic" ErrorMessage="Please enter a valid mileage amount."> </asp:CompareValidator>