CompareValidator Control

Definition and Usage

The CompareValidator control is used to compare the value of one input control to the value of another input control or to a fixed value.

Note: If the input control is empty, the validation will succeed. Use the RequiredFieldValidator control to make the field required.

Properties

Property	Description
BackColor	The background color of the CompareValidator control
ControlToCompare	The name of the control to compare with
ControlToValidate	The id of the control to validate
Display	The display behavior for the validation control. Legal values are: None (the control is not displayed. Used to show the error message only in the ValidationSummary control) Static (the control displays an error message if validation fails. Space is reserved on the page for the message even if the input passes validation. Dynamic (the control displays an error message if validation fails. Space is not reserved on the page for the message if the input passes validation
EnableClientScript	A Boolean value that specifies whether client-side validation is enabled or not
Enabled	A Boolean value that specifies whether the validation control is enabled or not
ErrorMessage	The text to display in the ValidationSummary control when validation fails. Note: This text will also be displayed in the validation control if the Text property is not set
ForeColor	The foreground color of the control
id	A unique id for the control
IsValid	A Boolean value that indicates whether the control specified by ControlToValidate is determined to be valid
Operator	The type of comparison to perform. The operators are: Equal GreaterThan GreaterThanEqual LessThan LessThanEqual NotEqual DataTypeCheck
runat	Specifies that the control is a server control. Must be set to "server"
Text	The message to display when validation fails
Type	Specifies the data type of the values to compare. The types are: Currency Date Double Integer String
ValueToCompare	A specified value to compare with

Example 1

In the following example we declare two TextBox controls, one CompareValidator control, one ListBox control, one Button control, and one Label control in an .aspx file. The check_valid() function checks if the page is valid. If it is valid, it returns "Valid!" in the Label control. If it is not valid, it returns "Not Valid!" in the Label control. The check_operator() function sets the operator of the CompareValidator control equal to the selected operator in the ListBox control, then it validates the CompareValidator control. If validation fails, the text "Validation Failed!" will be displayed in red on a yellow background in the CompareValidator control:

<script runat="server">
sub check_valid(sender As Object,e As EventArgs) 
if Page.IsValid then 
  mess.Text="Valid!"
else 
  mess.Text="Not valid!"
end if
end sub

sub check_operator(sender As Object,e As EventArgs) 
compval.Operator=CType(l1.SelectedIndex,ValidationCompareOperator)
compval.Validate()
end sub
</script>

<html>
<body>
<form runat="server">
<table bgcolor="#b0c4de">
  <tr valign="top">
    <td colspan="4">
      <h4>Enter a value in each textbox and select a comparison
      operator. Click "Validate" to compare the values.</h4>
    </td>
  </tr> 
  <tr valign="top">
    <td>
      <asp:TextBox id="txt1" runat="server"/><br />
      <asp:CompareValidator id="compval" 
      ControlToValidate="txt1" 
      ControlToCompare="txt2" 
      ForeColor="red" 
      BackColor="yellow" 
      Type="String"
      EnableClientScript="false" 
      Text="Validation Failed!" 
      runat="server"/>
    </td>
    <td>
      <asp:ListBox id="l1"
      OnSelectedIndexChanged="check_operator" runat="server">
        <asp:ListItem value="Equal" selected>=</asp:ListItem>
        <asp:ListItem value="NotEqual">&lt;&gt;</asp:ListItem>
        <asp:ListItem value="GreaterThan">&gt;</asp:ListItem>
        <asp:ListItem value="LessThan">&lt;</asp:ListItem>
      </asp:ListBox>
    </td>
    <td>
      <asp:TextBox id="txt2" runat="server"/>
    </td>
    <td>
      <asp:Button id="b1" Text="Validate"
      OnClick="check_valid" runat="server"/>
    </td>
  </tr>
</table>
<p>
<asp:Label id="mess" Font-Name="verdana"
Font-Size="14pt" runat="server"/>
</p>
</form>
</body>
</html>

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