yavsc/BookAStar/BookAStar/Converters/Behaviors/RegexValidatorBehavior.cs

using System;
using System.Text.RegularExpressions;
using Xamarin.Forms;

namespace BookAStar.Behaviors
{
    public class RegexValidatorBehavior : Behavior<Entry>
    {
        private string regexp = @"^([\d\w]+)$";
        // Creating BindableProperties with Limited write access: http://iosapi.xamarin.com/index.aspx?link=M%3AXamarin.Forms.BindableObject.SetValue(Xamarin.Forms.BindablePropertyKey%2CSystem.Object) 

        static readonly BindablePropertyKey IsValidPropertyKey = BindableProperty.CreateReadOnly("IsValid", typeof(bool), typeof(RegexValidatorBehavior), false);

        public static readonly BindableProperty IsValidProperty = IsValidPropertyKey.BindableProperty;

        public bool IsValid
        {
            get { return (bool)base.GetValue(IsValidProperty); }
            private set { base.SetValue(IsValidPropertyKey, value); }
        }

        protected string Regexp
        {
            get
            {
                return regexp;
            }

            set
            {
                regexp = value;
            }
        }

        protected override void OnAttachedTo(Entry bindable)
        {
            bindable.TextChanged += HandleTextChanged;
        }


        void HandleTextChanged(object sender, TextChangedEventArgs e)
        {
            IsValid = (Regex.IsMatch(e.NewTextValue, regexp, RegexOptions.IgnoreCase, TimeSpan.FromMilliseconds(250)));
            ((Entry)sender).TextColor = IsValid ? Color.Default : Color.Red;
        }

        protected override void OnDetachingFrom(Entry bindable)
        {
            bindable.TextChanged -= HandleTextChanged;

        }
    }
}