You can validate a user's entry against a specific single value using logical operators. For example, you can specify that the user's entry is a date after January 1, 1950 or that it is an integer value greater than or equal to zero. Alternatively, you can specify that the user's entry be compared against a value from another control.
To validate against a specific value
Property | Setting |
---|---|
ControlToValidate | The ID of the control to validate. |
ErrorMessage, Text, ValidationDisplay | Properties that specify the text and location of the error or errors that will display if the user skips the control. For details, see Controlling Validation Error Message Display. |
Note When validation is done against another control, invalid values in the other control are ignored and the validation passes. For details, see Special-Case Validation Results.
Note The validation control validates user input using the format specified by the page's locale setting .
Note If the user leaves a control blank, the control passes the comparison validation. To force the user to enter a value, add a RequiredField validation control as well. For details, see Validating a Required Entry.
The following shows an example in the .aspx file of a Web Form Textbox control with required field validation. A table is used to control layout.
<TABLE> <TR> <TD> <asp:Textbox id="txtAge" runat="server"></asp:Textbox> </TD> <TD> <asp:CompareValidator id="CompareFieldValidator1" runat="server" ForeColor="Red" ControlToValidate="txtAge" ValueToCompare=0 Type="Integer" Operator="GreaterThanEqual" ErrorMessage="Please enter a whole number zero or greater."> </asp: CompareValidator > </TD> </TR> </TABLE>
The following example shows a CompareValidator that compares the user's entry against the value in another control. In a form that allows users to make reservations at a hotel, the validator checks that the user does not enter a departure date earlier than the arrival date.
<TABLE> <TR> <TD> <asp:Textbox id="txtDepartureDate" runat="server"></asp:Textbox> </TD> <TD> <asp:CompareValidator id="CompareFieldValidator1" runat="server" ForeColor="Red" ControlToValidate="txtDepartureDate" ControlToCompare="txtArrivalDate" Type="DateTime" Operator="GreaterThanEqual" ErrorMessage="Departure date cannot be earlier than arrival date."> </asp: CompareValidator > </TD> </TR> </TABLE>
Validation Controls | Introduction to Validating User Input in Web Forms | Controlling Validation Error Message Display | Controlling Client versus Server Validation