I Create A Numerictextbox Extends From Texbox. How Can I Set A Custom Property "Ismust" Type Of Bool .How Can It Possible?

using System;
using System.Windows;
namespace CommonControlLibrary
{
    public partial class NumericTextbox : System.Windows.Controls.TextBox
    {
       

        public NumericTextbox()
            : base()
        {
            this.AddHandler(System.Windows.DataObject.PastingEvent, new System.Windows.DataObjectPastingEventHandler(this.TextBoxPasting));
        }

        protected override void OnPreviewTextInput(System.Windows.Input.TextCompositionEventArgs e)
        {
            base.OnPreviewTextInput(e);
            e.Handled = !IsTextAllowed(e.Text);
        }

        private bool IsTextAllowed(string text)
        {
            System.Text.RegularExpressions.Regex regex = new System.Text.RegularExpressions.Regex("[^0-9]+");
            return !regex.IsMatch(text);
        }

        private void TextBoxPasting(object sender, System.Windows.DataObjectPastingEventArgs e)
        {
            if (e.DataObject.GetDataPresent(typeof(System.String)))
            {
                System.String text = (System.String)e.DataObject.GetData(typeof(System.String));
                if (!IsTextAllowed(text))
                    e.CancelCommand();
            }

            else
                e.CancelCommand();

        }
    }
}