C#

public interface IValidatorCommand
{
  void Execute();
}

public class ValidationOutcome
{
  public bool Passed = true;
  public Type FailureType;
  public string Reason;
}
public abstract class ValidatorCommand : IValidatorCommand
{
  public ValidatorCommand()
  {
  }
  public override ValidationOutcome Execute() {}
}

public class RegexValidatorCommand : ValidatorCommand
{
  protected string regex;
  protected string text;
  protected RegexValidatorCommand(string regex, string text) 
  {
    this.text = text;
    this.regex = regex;
  }
  public static RegexValidatorCommand Validator(string regex, string text)
  {
    return new RegexValidatorCommand(regex, text);
  }

  public override ValidationOutcome Execute()
  {
    ValidationOutcome outcome = new ValidationOutcome();
    outcome.Type = this;
    // Do the validation here.
    if (...)
    {
      outcome.Reason = "The regex didn't match your input.";
      outcome.Passed = false;
    }
  }
}

ValidationOutcome outcome = RegexValidatorCommand.Validator("regex", txtMyTextbox.Text).Execute();
if (outcome.Passed)
{
  // Do something.
}
else
{
  // Tell the user.
}

R.Myers wrote:

can make a rectangle and have it follow the mouse movements, but i don't know how to redraw the underlying image to clear the dragging effect.