Data Validation in WPF

 
/// <summary>
/// Validates a text against a regular expression
/// </summary>
public class RegexValidationRule : ValidationRule
{
    private string _pattern;
    private Regex _regex;
 
    public string Pattern
    {
        get { return _pattern; }
        set
        {
            _pattern = value;
            _regex = new Regex(_pattern, RegexOptions.IgnoreCase);
        }
    }
 
    public RegexValidationRule()
    {
    }
 
    public override ValidationResult Validate(object value, CultureInfo ultureInfo)
    {
        if (value == null || !_regex.Match(value.ToString()).Success)
        {
            return new ValidationResult(false, "The value is not a valid e-mail address");
        }
        else
        {
            return new ValidationResult(true, null);
        }
    }
}
 
 

 
<Window.Resources>
        <sys:String x:Key="emailRegex">^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@
        [a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]
        *[a-zA-Z]$</sys:String>    
</Window.Resources>
 
 

 
[ValueConversion(typeof(ReadOnlyObservableCollection<ValidationError>), typeof(string))]
public class ValidationErrorsToStringConverter : MarkupExtension, IValueConverter
{
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return new ValidationErrorsToStringConverter();
    }
 
    public object Convert(object value, Type targetType, object parameter, 
        CultureInfo culture)
    {
        ReadOnlyObservableCollection<ValidationError> errors =
            value as ReadOnlyObservableCollection<ValidationError>;
 
        if (errors == null)
        {
            return string.Empty;
        }
 
        return string.Join("\n", (from e in errors 
                                  select e.ErrorContent as string).ToArray());
    }
 
    public object ConvertBack(object value, Type targetType, object parameter, 
        CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}
 
 

 
<ControlTemplate x:Key="TextBoxErrorTemplate" TargetType="Control">
    <Grid ClipToBounds="False" >
        <Image HorizontalAlignment="Right" VerticalAlignment="Top" 
               Width="16" Height="16" Margin="0,-8,-8,0" 
               Source="{StaticResource ErrorImage}" 
               ToolTip="{Binding ElementName=adornedElement, 
                         Path=AdornedElement.(Validation.Errors), 
                         Converter={k:ValidationErrorsToStringConverter}}"/>
        <Border BorderBrush="Red" BorderThickness="1" Margin="-1">
            <AdornedElementPlaceholder Name="adornedElement" />
        </Border>
    </Grid>
</ControlTemplate>
 

 
<TextBox x:Name="txtEMail" Template={StaticResource TextBoxErrorTemplate}>
    <TextBox.Text>
        <Binding Path="EMail" UpdateSourceTrigger="PropertyChanged" >
            <Binding.ValidationRules>
                <local:RegexValidationRule Pattern="{StaticResource emailRegex}"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>
 
 

 
private void ForceValidation()
{
  txtName.GetBindingExpression(TextBox.TextProperty).UpdateSource();    
}