Regular Expression Validator Control Sample
The regular expression validator control shown here extends the base validator control described in the Base Validator Control Sample. This validator adds the following functionality to the base validator:
- It exposes a property named
ValidationExpression
that allows a user (page developer) to specify a regular expression. - It overrides the
EvaluateIsValid
method (defined as an abstract method inBaseDomValidator
) to provide logic to determine whether the field to validate matches the pattern specified by the regular expression. - It overrides AddAttributesToRender (inherited from WebControl) to provide a client-side handler for the evaluation logic. The client-side handler is a function defined in the script library.
To compile and build this sample, see the instructions in Validator Control Samples. For an overview of client-side scripting in server controls, see Client-Side Functionality in a Server Control.
// RegexDomValidator.cs.
namespace DomValidators {
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Diagnostics;
using System.Text.RegularExpressions;
using System.Drawing.Design;
using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
[
ToolboxData("<{0}:RegexDomValidator runat=server ErrorMessage=\"RegexDomValidator\"></{0}:RegexDomValidator>")
]
public class RegexDomValidator : BaseDomValidator {
[
Bindable(true),
Category("Behavior"),
DefaultValue(""),
Editor("System.Web.UI.Design.WebControls.RegexTypeEditor,System.Design", typeof(UITypeEditor)),
Description("ValidationExpression")
]
public string ValidationExpression {
get {
object o = ViewState["ValidationExpression"];
return((o == null) ? String.Empty : (string)o);
}
set {
try {
Regex.IsMatch("", value);
}
catch (Exception e) {
//Throw new HttpException.
// HttpRuntime.FormatResourceString(SR.Validator_bad_regex, value), e);
throw new HttpException("Bad Expression", e);
}
ViewState["ValidationExpression"] = value;
}
}
protected override void AddAttributesToRender(HtmlTextWriter writer) {
base.AddAttributesToRender(writer);
if (RenderUplevel) {
writer.AddAttribute("evaluationfunction", "RegularExpressionValidatorEvaluateIsValid");
if (ValidationExpression.Length > 0) {
writer.AddAttribute("validationexpression", ValidationExpression);
}
}
}
protected override bool EvaluateIsValid() {
// Validation always succeeds if input is empty or value was not found.
string controlValue = GetControlValidationValue(ControlToValidate);
Debug.Assert(controlValue != null, "Should have already been checked");
if (controlValue == null || controlValue.Length == 0) {
return true;
}
try {
// Looking for an exact match, not just a search hit.
Match m = Regex.Match(controlValue, ValidationExpression);
return(m.Success && m.Index == 0 && m.Length == controlValue.Length);
}
catch {
Debug.Fail("Regex error should have been caught in property setter.");
return true;
}
}
}
}
[Visual Basic]
' RegexDomValidator.vb
Option Explicit
Option Strict
Imports System.ComponentModel
Imports System.ComponentModel.Design
Imports System.Diagnostics
Imports System.Text.RegularExpressions
Imports System.Drawing.Design
Imports System
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls
Namespace DomValidators
<ToolboxData("<{0}:RegexDomValidator runat=server ErrorMessage=""RegexDomValidator""></{0}:RegexDomValidator>")> _
Public Class RegexDomValidator
Inherits BaseDomValidator
<Bindable(True), _
Category("Behavior"), _
DefaultValue(""), _
Editor("System.Web.UI.Design.WebControls.RegexTypeEditor,System.Design", _
GetType(UITypeEditor)), _
Description("ValidationExpression")> _
Public Property ValidationExpression() As String
Get
Dim o As Object = ViewState("ValidationExpression")
If o Is Nothing Then
Return String.Empty
Else
Return CStr(o)
End If
End Get
Set
Try
Regex.IsMatch("", value)
Catch e As Exception
'Throw new HttpException.
' HttpRuntime.FormatResourceString(SR.Validator_bad_regex, value), e);
Throw New HttpException("Bad Expression", e)
End Try
ViewState("ValidationExpression") = value
End Set
End Property
Protected Overrides Sub AddAttributesToRender(writer As HtmlTextWriter)
MyBase.AddAttributesToRender(writer)
If RenderUplevel Then
writer.AddAttribute("evaluationfunction", "RegularExpressionValidatorEvaluateIsValid")
If ValidationExpression.Length > 0 Then
writer.AddAttribute("validationexpression", ValidationExpression)
End If
End If
End Sub
Protected Overrides Function EvaluateIsValid() As Boolean
' Always succeeds if input is empty or value was not found.
Dim controlValue As String = GetControlValidationValue(ControlToValidate)
Debug.Assert( Not (controlValue Is Nothing), "Should have already been checked")
If controlValue Is Nothing Or controlValue.Length = 0 Then
Return True
End If
Try
' Looking for an exact match, not just a search hit.
Dim m As Match = Regex.Match(controlValue, ValidationExpression)
Return m.Success And m.Index = 0 And m.Length = controlValue.Length
Catch
End Try
End Function
End Class
End Namespace
See Also
Validator Control Samples | Base Validator Control Sample | Required Field Validator Control Sample | Script Library for Validator Sample | Configuration File for Validator Sample | Test Page for Validator Sample | Developing a Validator Control