Login page is not validating in xamarin form

Question

I have created login page using xamarin forms and created the class file called validationbehaviour.cs and validated input fields through behaviour class.

xaml login

Answer 1

Maybe you should change IsValid variable to property like this:

using System;         
using System.Collections.Generic;     
using System.Linq;     
using System.Text;        
using System.Threading.Tasks;    
using Xamarin.Forms;      
using System.Text.RegularExpressions;   

namespace LoginUser   
{    
    public class ValidationBehavior: Behavior<Entry>   
    {    
        const string pwRegex = @"^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^\da-zA-Z]).{8,15}$";            

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

        public static readonly BindableProperty IsValidProperty = IsValidPropertyKey.BindableProperty;

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

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

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

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

    }
}

Another error is also your regular expression, try the following:

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).{8,15}$

If you also want to require at least one special character (which is probably a good idea), try this:

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^\da-zA-Z]).{8,15}$

With my sample you get like this:

With password: 123456

With password: AbcDe12!