MainPage.xaml

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             x:Class="EntryValidationBorder.MainPage"
             xmlns:local="clr-namespace:EntryValidationBorder"
             xmlns:behavior="clr-namespace:EntryValidationBorder.Behavior">
	<ContentPage.Content>
        <StackLayout VerticalOptions="CenterAndExpand" Padding="20" x:Name="layout">
                <local:ExtendedEntry Placeholder="Name" ErrorText="{Binding User.FirstName.NotValidMessageError}"
                                     BorderErrorColor="Red"
                                     Text="{Binding User.FirstName.Name}"
                                     HeightRequest="40"
                                     IsBorderErrorVisible="{Binding User.FirstName.IsNotValid, Mode=TwoWay}">
                                 <local:ExtendedEntry.Behaviors>
                                         <behavior:EmptyEntryValidatorBehavior />
                                  </local:ExtendedEntry.Behaviors>
               </local:ExtendedEntry>
            
                <local:ExtendedEntry Placeholder="Email" ErrorText="{Binding User.Email.NotValidMessageError}"
                                     BorderErrorColor="Red"
                                     Text="{Binding User.Email.Name}"
                                     HeightRequest="40"
                                     IsBorderErrorVisible="{Binding User.Email.IsNotValid, Mode=TwoWay}">
                                 <local:ExtendedEntry.Behaviors>
                                         <behavior:EmptyEntryValidatorBehavior />
                                  </local:ExtendedEntry.Behaviors>
               </local:ExtendedEntry>

              <local:ExtendedEntry Placeholder="Password" ErrorText="{Binding User.Password.NotValidMessageError}"
                                    BorderErrorColor="Red" IsPassword="true"
                                     Text="{Binding User.Password.Name}"
                                     HeightRequest="40"
                                     IsBorderErrorVisible="{Binding User.Password.IsNotValid, Mode=TwoWay}">
                                 <local:ExtendedEntry.Behaviors>
                                         <behavior:EmptyEntryValidatorBehavior />
                                  </local:ExtendedEntry.Behaviors>
               </local:ExtendedEntry>

              <Button Text="Enter" 
                      Command="{Binding OnValidationCommand}"
                      BackgroundColor="Black"
                      HorizontalOptions="FillAndExpand"
                      TextColor="White"/>
        </StackLayout>
	</ContentPage.Content>
</ContentPage>