6.3 Validation Controls
6.3 Validation ControlsASP.NET provides six built-in validation controls. These controls provide four types of validation, as well as a way to summarize errors and a way to construct your own validation algorithms.
The
BaseValidator
class is used as the base class for all the validation controls, providing a single generic implementation of many of the validation capabilities. Listing 6-4 shows a partial definition of the class. Note that it implements the
IValidator
interface and derives from
Label
. By deriving from the
Label
control, the
BaseValidator
class inherits the span-rendering capabilities of that class, which is
Listing 6-4 The BaseValidator Class
public abstract class BaseValidator : Label, IValidator
{
protected BaseValidator();
// Properties
public static PropertyDescriptor
GetValidationProperty(object component) {}
public ValidatorDisplay Display {get; set; }
public bool Enabled {override get; override set; }
public string ErrorMessage {get; set; }
public Color ForeColor {override get; override set; }
public bool IsValid {get; set; }
// Methods
public void Validate();
protected void CheckControlValidationProperty(string name, string propertyName);
protected abstract bool EvaluateIsValid();
protected string GetControlRenderID(string name);
protected string GetControlValidationValue(string name);
protected void RegisterValidatorCommonScript();
protected void RegisterValidatorDeclaration();
//...
}
For a control to be
Figure 6-6. Controls That Can Be Used with Validation Controls
Six validation controls are available in ASP.NET. The
RequiredFieldValidator
, as we have seen already, is used to verify that a field is not left empty. The
ValidationSummary
control is used to display a summary of all the error messages on a given form and
It is important to note that for all these controls except the
RequiredFieldValidator
, an empty field is
Table 6-1. Validation Controls and Their Properties
The
ValidationSummary
control culls all the
ErrorMessage
s of each validation control on a page and displays them in a bullet list, a plain list, or a single paragraph format. Listing 6-5 shows the
ValidationSummary
control and its additional properties. The
HeaderText
property defines the title string for the summary of error messages. The
ShowMessageBox
property causes a message box with the summary of errors to appear when the
Listing 6-5 ValidationSummary Control Example
<! File: ValidationSummary.aspx >
<html><body>
<form runat=server>
<table cellspacing=0 cellpadding=2 border=0>
<tr><td><table cellspacing=0 cellpadding=1 border=0>
<tr><td align=right><b>Name:</b></td>
<td><asp:TextBox id="cname" runat=server/></td>
<td><asp:RequiredFieldValidator id="cnameValidator"
ControlToValidate="cname"
Display="Static"
ErrorMessage="Name must be filled in."
InitialValue="" runat=server>*
</asp:RequiredFieldValidator>
</td></tr>
<tr><td align=right><b>Phone:</b></td>
<td><asp:TextBox id="phone" runat=server/></td>
<td><asp:RequiredFieldValidator id="phoneValidator"
ControlToValidate="phone"
Display="Static"
ErrorMessage="Phone must be filled in."
InitialValue="" runat=server>*
</asp:RequiredFieldValidator>
</td></tr>
<tr><td></td>
<td><input value="Enter" type=submit /></td>
</tr></table><td>
<asp:ValidationSummary id="valSum" runat=server
HeaderText="Please correct the following errors:"
ShowMessageBox="True"/></td></tr>
</table>
</form>
</body></html>
Listing 6-6 shows the
CompareValidator
control and its additional properties. The
Operator
property defines what comparison operation to perform, and the
Type
property specifies the type of the two values to compare. Either the
ValueToCompare
or the
ControlToCompare
property contains the value (or reference to a field containing the value) to compare with the target input. Listing 6-6 shows an example of using the
CompareValidator
control to verify that the user is over 21
Listing 6-6 CompareValidator Control Example
<! File: CompareValidator.aspx >
<%@ Page %>
<html>
<body>
<h1>Compare Validator Example</h1>
<form runat="server">
Age: <asp:TextBox id="_age" runat=server/>
<asp:CompareValidator id="ageValidator"
ControlToValidate="_age"
ValueToCompare="21"
Type="Integer"
Operator="GreaterThan" runat=server>
You must be over 21!
</asp:CompareValidator>
<br/>
<input value="Enter" type=submit />
</form>
</body> </html>
Listing 6-7 shows the
RegularExpressionValidator
control with its one additional property:
ValidationExpression
. With this control, you can specify any JavaScript regular expression to validate a field. Listing 6-7 shows an example of validating a zip code to ensure that it is of the correct format. Table 6-2 shows some of the more common regular expression
Listing 6-7 RegularExpressionValidator Control Example
<! File: RegularExpressionValidator.aspx >
<%@ Page %>
<html>
<body>
<h1>Regular Expression Validator Example</h1>
<form runat="server">
Zipcode:<asp:TextBox id="_zipcode"
runat=server/><asp:RegularExpressionValidator
ControlToValidate="_zipcode"
Display="static"
ErrorMessage="Zip code must be of the form 11111-1111"
InitialValue="" width="100%" runat=server
ValidationExpression="\d{5}(-\d{4})?">**
</asp:RegularExpressionValidator>
<br/>
<input value="Enter" type=submit />
</form>
</body> </html>
Table 6-2. Some Regular Expression Characters and Their Meaning
The
CustomValidator
control lets you define your own validation function to perform whatever arbitrary validation you would like on a field. In keeping with the other validation controls, you can provide both a client-side validation routine (in JavaScript) and a server-side validation routine. Listing 6-8 shows an example of using a
CustomValidator
control to verify that a number is divisible by three. Note that two script sections are defined ”one client script and one server script ”each containing a validation function that
Listing 6-8 CustomValidator Control Example
<! File: CustomValidator.aspx >
<%@ Page Language="C#" %>
<script language=javascript>
<!
function ValModThreeClient(source, args)
{
if (args.value % 3)
args.IsValid=false;
else
args.IsValid=true;
}
>
</script>
<script language="C#" runat=server>
void ValModThreeServer(object source,
ServerValidateEventArgs e)
{
e.IsValid = false;
try
{
int num = Convert.ToInt32(e.Value);
if (num % 3 == 0)
e.IsValid = true;
}
catch (Exception)
{}
}
</script>
<html>
<body>
<h1>Custom Validator Example</h1>
<form runat="server">
Number: <asp:TextBox id="_num" runat=server/>
<asp:CustomValidator id="numValidator"
ControlToValidate="_num"
Display="static"
InitialValue=""
ClientValidationFunction = "ValModThreeClient"
OnServerValidate = "ValModThreeServer"
width="100%"
ErrorMessage="Please enter a value divisible by three" runat=server/>
<br/>
<input value="Enter" type=submit />
</form>
</body> </html>
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