WPF: ValidationRules
Overview
ValidationRules is a class, which provides a way to create a custom rule in order to check the validity of a user input. These ValidationRules are specific to WPF, they did not get carried over to Silverlight, Windows phone or Windows 8 XAML technologies.
What you do is define a class that inherits from a ValidationRule base class, and then you override a validate method that’s an abstract method in the base class. That Validate method returns a ValidationResult Object, which includes a flag to indicate success or failure, a Boolean, and an error message that can be associated with it. Once you have the ValidationRule defined, you go and you hook it up to a ValidationRules collection that’s on a binding.
Demo
Create a WPF application. Create a class that implements ValidationRule and override the Validate method. Here you can write the validation rule for your application. Give a regular expression to validate email id.
public class RegexValidation : ValidationRule
{
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
Regex regex = new Regex(@"^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$");
Match match = regex.Match(value.ToString());
if (match == null || match == Match.Empty)
{
return new ValidationResult(false, "Please enter valid email");
}
else
{
return ValidationResult.ValidResult;
}
}
}
Inside MainWindow class, create one property
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private string email;
public string Email
{
get { return email; }
set { email = value; }
}
}
In XAML, Bind the property and specify the validation rule here.
<StackPanel>
<TextBox Margin="5" Height="30"
Width="200" >
<TextBox.Text>
<Binding Path="Email" ElementName="thiswindow" >
<Binding.ValidationRules>
<local:RegexValidation></local:RegexValidation>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
<TextBox Margin="5" Height="30" Width="200" ></TextBox>
</StackPanel>
Run the application and type any invalid email address and hit enter, you can see a red box on the email address textbox. This is coming from our regular expression validation.
