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Example E4575
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WPF Data Editors - Create a Registration Form

This example is the application from the Create a Registration Form tutorial. The solution includes projects for each completed tutorial step.

BaseProject

This project is a draft application connected to a database. The project contains two predefined views: MainView with the DXTabControl and RecordsView with the GridControl:

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Documentation

Lesson1

This project uses the LayoutControl to arrange data editors within the RegistrationView:

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Documentation

Lesson2

This project binds data editors to View Model properties:

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Documentation

Lesson3

This project defines data editor settings (null text, mask, min and max values, popup mode, and data source):

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Lesson4

This project uses ValidationRules to implement input validation and disables the Register button if editors contain validation errors:

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Lesson5

This project uses the IDataErrorInfo interface to obtain validation errors and displays a message box with the registration result:

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Example Code

RegistrationForm.BaseProject/View/MainView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.MainView" 
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             xmlns:View="clr-namespace:RegistrationForm.View"
             mc:Ignorable="d" d:DesignHeight="500" d:DesignWidth="500"
             DataContext="{dxmvvm:ViewModelSource ViewModel:MainViewModel}">
    <dxmvvm:Interaction.Behaviors>
        <dx:DXMessageBoxService/>
    </dxmvvm:Interaction.Behaviors>
    <Grid x:Name="root">
        <dx:DXTabControl TabContentCacheMode="CacheAllTabs">
            <dx:DXTabControl.View>
                <dx:TabControlScrollView HeaderLocation="Bottom" HeaderOrientation="Horizontal" ScrollButtonShowMode="Never"/>
            </dx:DXTabControl.View>
            <dx:DXTabItem Header="Registration Form">
                <View:RegistrationView Width="300" dxmvvm:ViewModelExtensions.ParentViewModel="{Binding ElementName=root, Path=DataContext}"/>
            </dx:DXTabItem>
            <dx:DXTabItem Header="Records">
                <View:RecordsView dxmvvm:ViewModelExtensions.ParentViewModel="{Binding ElementName=root, Path=DataContext}"/>
            </dx:DXTabItem>
        </dx:DXTabControl>
    </Grid>
</UserControl>
RegistrationForm.BaseProject/ViewModel/MainViewModel.cs(vb) 
C#
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.POCO;

namespace RegistrationForm.ViewModel {
    [POCOViewModel]
    public class MainViewModel {
        public static MainViewModel Create() {
            return ViewModelSource.Create(() => new MainViewModel());
        }
        protected MainViewModel() { }
    }
}
RegistrationForm.BaseProject/View/RecordsView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.RecordsView" 
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:dxg="http://schemas.devexpress.com/winfx/2008/xaml/grid"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             mc:Ignorable="d" d:DesignHeight="450" d:DesignWidth="400"
             DataContext="{dxmvvm:ViewModelSource ViewModel:RecordsViewModel}">
    <Grid>
        <dxg:GridControl Name="grid" AutoGenerateColumns="AddNew" ItemsSource="{Binding Employees}">
            <dxg:GridControl.View>
                <dxg:TableView Name="view" ShowGroupPanel="False" AllowEditing="False" AutoWidth="True"/>
            </dxg:GridControl.View>
        </dxg:GridControl>
    </Grid>
</UserControl>
RegistrationForm.BaseProject/ViewModel/RecordsViewModel.cs 
C#
using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.POCO;
using RegistrationForm.DataModel;
using System.Collections.Generic;

namespace RegistrationForm.ViewModel {
    [POCOViewModel]
    public class RecordsViewModel {
        public static RecordsViewModel Create() {
            return ViewModelSource.Create(() => new RecordsViewModel());
        }
        protected RecordsViewModel() {
            Messenger.Default.Register<DBEmployeesChangedMessage>(this, OnDBEmployeesChanged);
            Employees = new List<Employee>();
            if(!this.IsInDesignMode())
                InitializeEmployees();
        }
        void InitializeEmployees() {
            Employees = EmployeesModelHelper.GetEmployees();
        }
        void OnDBEmployeesChanged(DBEmployeesChangedMessage message) {
            InitializeEmployees();
        }

        public virtual List<Employee> Employees { get; set; }
    }
}
RegistrationForm.Lesson1/View/RegistrationView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.RegistrationView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             xmlns:dxlc="http://schemas.devexpress.com/winfx/2008/xaml/layoutcontrol" 
             xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" 
             mc:Ignorable="d" d:DesignHeight="450" d:DesignWidth="400"
             DataContext="{dxmvvm:ViewModelSource {x:Type ViewModel:RegistrationViewModel}}">
    <UserControl.Resources>
        <Style x:Key="labelStyle" TargetType="dxlc:LayoutItemLabel">
            <Setter Property="FontWeight" Value="Bold"/>
        </Style>
        <Style x:Key="itemStyle" TargetType="dxlc:LayoutItem">
            <Setter Property="LabelPosition" Value="Top"/>
            <Setter Property="LabelStyle" Value="{StaticResource labelStyle}"/>
        </Style>
    </UserControl.Resources>
    <Grid>
        <dxlc:LayoutControl Orientation="Vertical" ItemStyle="{StaticResource itemStyle}" ItemSpace="10">
            <dxlc:LayoutGroup ItemSpace="10">
                <dxlc:LayoutItem Label="Name">
                    <dxe:TextEdit />
                </dxlc:LayoutItem>
                <dxe:TextEdit VerticalAlignment="Bottom" />
            </dxlc:LayoutGroup>
            <dxlc:LayoutItem Label="Email">
                <dxe:TextEdit />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Create a password">
                <dxe:PasswordBoxEdit />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Confirm your password">
                <dxe:PasswordBoxEdit />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Birthday">
                <dxe:DateEdit />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Gender">
                <dxe:ComboBoxEdit />
            </dxlc:LayoutItem>
            <Button Content="Register" HorizontalAlignment="Center" VerticalAlignment="Bottom" Width="80" />
        </dxlc:LayoutControl>
    </Grid>
</UserControl>
RegistrationForm.Lesson2/View/RegistrationView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.RegistrationView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             xmlns:dxlc="http://schemas.devexpress.com/winfx/2008/xaml/layoutcontrol" 
             xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" 
             mc:Ignorable="d" d:DesignHeight="450" d:DesignWidth="400"
             DataContext="{dxmvvm:ViewModelSource {x:Type ViewModel:RegistrationViewModel}}">
    <UserControl.Resources>
        <Style x:Key="labelStyle" TargetType="dxlc:LayoutItemLabel">
            <Setter Property="FontWeight" Value="Bold"/>
        </Style>
        <Style x:Key="itemStyle" TargetType="dxlc:LayoutItem">
            <Setter Property="LabelPosition" Value="Top"/>
            <Setter Property="LabelStyle" Value="{StaticResource labelStyle}"/>
        </Style>
    </UserControl.Resources>
    <Grid>
        <dxlc:LayoutControl Orientation="Vertical" ItemStyle="{StaticResource itemStyle}" ItemSpace="10">
            <dxlc:LayoutGroup ItemSpace="10">
                <dxlc:LayoutItem Label="Name">
                    <dxe:TextEdit EditValue="{Binding FirstName}" />
                </dxlc:LayoutItem>
                <dxe:TextEdit VerticalAlignment="Bottom" EditValue="{Binding LastName}" />
            </dxlc:LayoutGroup>
            <dxlc:LayoutItem Label="Email">
                <dxe:TextEdit EditValue="{Binding Email}" />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Create a password">
                <dxe:PasswordBoxEdit EditValue="{Binding Password}" />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Confirm your password">
                <dxe:PasswordBoxEdit EditValue="{Binding ConfirmPassword}" />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Birthday">
                <dxe:DateEdit EditValue="{Binding Birthday}" />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Gender">
                <dxe:ComboBoxEdit EditValue="{Binding Gender}" />
            </dxlc:LayoutItem>
            <Button Content="Register" HorizontalAlignment="Center" VerticalAlignment="Bottom" Width="80" 
                    Command="{Binding AddEmployeeCommand}" />
        </dxlc:LayoutControl>
    </Grid>
</UserControl>
RegistrationForm.Lesson2/ViewModel/RegistrationViewModel.cs 
C#
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.POCO;
using RegistrationForm.DataModel;
using System;

namespace RegistrationForm.ViewModel {
    [POCOViewModel]
    public class RegistrationViewModel {
        public static RegistrationViewModel Create() {
            return ViewModelSource.Create(() => new RegistrationViewModel());
        }
        protected RegistrationViewModel() {
            if(this.IsInDesignMode())
                InitializeInDesignMode();
            else InitializeInRuntime();
        }
        void InitializeInDesignMode() {
            FirstName = "John";
            LastName = "Smith";
            Email = "John.Smith@JohnSmithMail.com";
            Password = "Password";
            ConfirmPassword = "Password";
            Birthday = new DateTime(1980, 1, 1);
            Gender = 1;
        }
        void InitializeInRuntime() {
            Birthday = null;
            Gender = -1;
        }

        public virtual string FirstName { get; set; }
        public virtual string LastName { get; set; }
        public virtual string Email { get; set; }
        public virtual string Password { get; set; }
        public virtual string ConfirmPassword { get; set; }
        public virtual DateTime? Birthday { get; set; }
        public virtual int Gender { get; set; }

        public void AddEmployee() {
            EmployeesModelHelper.AddNewEmployee(FirstName, LastName, Email, Password, Birthday.Value, Gender);
        }
    }
}
RegistrationForm.Lesson3/View/RegistrationView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.RegistrationView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             xmlns:DataModel="clr-namespace:RegistrationForm.DataModel"
             xmlns:dxlc="http://schemas.devexpress.com/winfx/2008/xaml/layoutcontrol" 
             xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" 
             xmlns:sys="clr-namespace:System;assembly=mscorlib"
             mc:Ignorable="d" d:DesignHeight="450" d:DesignWidth="400"
             DataContext="{dxmvvm:ViewModelSource {x:Type ViewModel:RegistrationViewModel}}">
    <UserControl.Resources>
        <Style x:Key="labelStyle" TargetType="dxlc:LayoutItemLabel">
            <Setter Property="FontWeight" Value="Bold"/>
        </Style>
        <Style x:Key="itemStyle" TargetType="dxlc:LayoutItem">
            <Setter Property="LabelPosition" Value="Top"/>
            <Setter Property="LabelStyle" Value="{StaticResource labelStyle}"/>
        </Style>
    </UserControl.Resources>
    <Grid>
        <dxlc:LayoutControl Orientation="Vertical" ItemStyle="{StaticResource itemStyle}" ItemSpace="10">
            <dxlc:LayoutGroup ItemSpace="10">
                <dxlc:LayoutItem Label="Name">
                    <dxe:TextEdit EditValue="{Binding FirstName}" NullText="FIRST"/>
                </dxlc:LayoutItem>
                <dxe:TextEdit VerticalAlignment="Bottom" EditValue="{Binding LastName}" NullText="LAST"/>
            </dxlc:LayoutGroup>
            <dxlc:LayoutItem Label="Email">
                <dxe:TextEdit EditValue="{Binding Email}" MaskType="RegEx"
                              Mask="[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}"
                              MaskIgnoreBlank="True" InvalidValueBehavior="AllowLeaveEditor" />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Create a password">
                <dxe:PasswordBoxEdit EditValue="{Binding Password}" />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Confirm your password">
                <dxe:PasswordBoxEdit EditValue="{Binding ConfirmPassword}" />
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Birthday">
                <dxe:DateEdit EditValue="{Binding Birthday}" InvalidValueBehavior="AllowLeaveEditor"
                              MinValue="{Binding MinBirthday}" MaxValue="{Binding MaxBirthday}">
                    <dxe:DateEdit.StyleSettings>
                        <dxe:DateEditPickerStyleSettings/>
                    </dxe:DateEdit.StyleSettings>
                </dxe:DateEdit>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Gender">
                <dxe:ComboBoxEdit EditValue="{Binding Gender}" NullText="I am..."
                                  ItemsSource="{x:Static Member=DataModel:GenderList.Source}" 
                                  ValueMember="ID" DisplayMember="Description">
                    <dxe:ComboBoxEdit.NullValue>
                        <sys:Int32>-1</sys:Int32>
                    </dxe:ComboBoxEdit.NullValue>
                </dxe:ComboBoxEdit>
            </dxlc:LayoutItem>
            <Button Content="Register" HorizontalAlignment="Center" VerticalAlignment="Bottom" Width="80" 
                    Command="{Binding AddEmployeeCommand}" />
        </dxlc:LayoutControl>
    </Grid>
</UserControl>
RegistrationForm.Lesson3/ViewModel/RegistrationViewModel.cs 
C#
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.POCO;
using RegistrationForm.DataModel;
using System;

namespace RegistrationForm.ViewModel {
    [POCOViewModel]
    public class RegistrationViewModel {
        public static RegistrationViewModel Create() {
            return ViewModelSource.Create(() => new RegistrationViewModel());
        }
        protected RegistrationViewModel() {
            MinBirthday = new DateTime(DateTime.Now.Year - 100, 12, 31);
            MaxBirthday = new DateTime(DateTime.Now.Year - 1, 12, 31);
            if(this.IsInDesignMode())
                InitializeInDesignMode();
            else InitializeInRuntime();
        }
        void InitializeInDesignMode() {
            FirstName = "John";
            LastName = "Smith";
            Email = "John.Smith@JohnSmithMail.com";
            Password = "Password";
            ConfirmPassword = "Password";
            Birthday = new DateTime(1980, 1, 1);
            Gender = 1;
        }
        void InitializeInRuntime() {
            Birthday = null;
            Gender = -1;
        }

        public virtual string FirstName { get; set; }
        public virtual string LastName { get; set; }
        public virtual string Email { get; set; }
        public virtual string Password { get; set; }
        public virtual string ConfirmPassword { get; set; }
        public virtual DateTime? Birthday { get; set; }
        public virtual DateTime MinBirthday { get; set; }
        public virtual DateTime MaxBirthday { get; set; }
        public virtual int Gender { get; set; }

        public void AddEmployee() {
            EmployeesModelHelper.AddNewEmployee(FirstName, LastName, Email, Password, Birthday.Value, Gender);
        }
    }
}
RegistrationForm.Lesson4/View/RegistrationView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.RegistrationView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             xmlns:DataModel="clr-namespace:RegistrationForm.DataModel"
             xmlns:Common="clr-namespace:RegistrationForm.Common"
             xmlns:dxlc="http://schemas.devexpress.com/winfx/2008/xaml/layoutcontrol" 
             xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" 
             xmlns:sys="clr-namespace:System;assembly=mscorlib"
             mc:Ignorable="d" d:DesignHeight="450" d:DesignWidth="400"
             DataContext="{dxmvvm:ViewModelSource {x:Type ViewModel:RegistrationViewModel}}">
    <UserControl.Resources>
        <Style x:Key="labelStyle" TargetType="dxlc:LayoutItemLabel">
            <Setter Property="FontWeight" Value="Bold"/>
        </Style>
        <Style x:Key="itemStyle" TargetType="dxlc:LayoutItem">
            <Setter Property="LabelPosition" Value="Top"/>
            <Setter Property="LabelStyle" Value="{StaticResource labelStyle}"/>
        </Style>
    </UserControl.Resources>
    <Grid>
        <dxlc:LayoutControl x:Name="container" dxe:ValidationService.IsValidationContainer="True"
                            Orientation="Vertical" ItemStyle="{StaticResource itemStyle}" ItemSpace="10">
            <dxlc:LayoutGroup ItemSpace="10">
                <dxlc:LayoutItem Label="Name">
                    <dxe:TextEdit NullText="FIRST" ValidateOnEnterKeyPressed="True" ValidateOnTextInput="False">
                        <dxe:TextEdit.EditValue>
                            <Binding Path="FirstName" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">
                                <Binding.ValidationRules>
                                    <Common:RequiredValidationRule FieldName="First Name"/>
                                </Binding.ValidationRules>
                            </Binding>
                        </dxe:TextEdit.EditValue>
                    </dxe:TextEdit>
                </dxlc:LayoutItem>
                <dxe:TextEdit VerticalAlignment="Bottom" NullText="LAST">
                    <dxe:TextEdit.EditValue>
                        <Binding Path="LastName" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">
                            <Binding.ValidationRules>
                                <Common:RequiredValidationRule FieldName="Last Name"/>
                            </Binding.ValidationRules>
                        </Binding>
                    </dxe:TextEdit.EditValue>
                </dxe:TextEdit>
            </dxlc:LayoutGroup>
            <dxlc:LayoutItem Label="Email">
                <dxe:TextEdit MaskType="RegEx"
                              Mask="[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}"
                              MaskIgnoreBlank="True" InvalidValueBehavior="AllowLeaveEditor">
                    <dxe:TextEdit.EditValue>
                        <Binding Path="Email" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">
                            <Binding.ValidationRules>
                                <Common:RequiredValidationRule FieldName="Email"/>
                            </Binding.ValidationRules>
                        </Binding>
                    </dxe:TextEdit.EditValue>
                </dxe:TextEdit>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Create a password">
                <dxe:PasswordBoxEdit>
                    <dxe:PasswordBoxEdit.EditValue>
                        <Binding Path="Password" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">
                            <Binding.ValidationRules>
                                <Common:RequiredValidationRule FieldName="Password"/>
                            </Binding.ValidationRules>
                        </Binding>
                    </dxe:PasswordBoxEdit.EditValue>
                </dxe:PasswordBoxEdit>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Confirm your password">
                <dxe:PasswordBoxEdit EditValue="{Binding ConfirmPassword}" 
                                     ValidateOnEnterKeyPressed="True" ValidateOnTextInput="True"/>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Birthday">
                <dxe:DateEdit InvalidValueBehavior="AllowLeaveEditor"
                              MinValue="{Binding MinBirthday}" MaxValue="{Binding MaxBirthday}">
                    <dxe:DateEdit.EditValue>
                        <Binding Path="Birthday" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">
                            <Binding.ValidationRules>
                                <Common:RequiredValidationRule FieldName="Birthday"/>
                            </Binding.ValidationRules>
                        </Binding>
                    </dxe:DateEdit.EditValue>
                    <dxe:DateEdit.StyleSettings>
                        <dxe:DateEditPickerStyleSettings/>
                    </dxe:DateEdit.StyleSettings>
                </dxe:DateEdit>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Gender">
                <dxe:ComboBoxEdit NullText="I am..."
                                  ItemsSource="{x:Static Member=DataModel:GenderList.Source}" 
                                  ValueMember="ID" DisplayMember="Description">
                    <dxe:ComboBoxEdit.EditValue>
                        <Binding Path="Gender" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay">
                            <Binding.ValidationRules>
                                <Common:RequiredValidationRule FieldName="Gender"/>
                            </Binding.ValidationRules>
                        </Binding>
                    </dxe:ComboBoxEdit.EditValue>
                    <dxe:ComboBoxEdit.NullValue>
                        <sys:Int32>-1</sys:Int32>
                    </dxe:ComboBoxEdit.NullValue>
                </dxe:ComboBoxEdit>
            </dxlc:LayoutItem>
            <Button Content="Register" HorizontalAlignment="Center" VerticalAlignment="Bottom" Width="80" 
                    Command="{Binding AddEmployeeCommand}" 
                    IsEnabled="{Binding ElementName=container, Path=(dxe:ValidationService.HasValidationError), Converter={dxmvvm:BooleanNegationConverter}}"/>
        </dxlc:LayoutControl>
    </Grid>
</UserControl>
RegistrationForm.Lesson4/Common/ValidationRules.cs(vb) 
C#
using DevExpress.Mvvm;
using System;
using System.Globalization;
using System.Linq.Expressions;
using System.Windows.Controls;

namespace RegistrationForm.Common {
    public class RequiredValidationRule : ValidationRule {
        public static string GetErrorMessage(string fieldName, object fieldValue, object nullValue = null) {
            string errorMessage = string.Empty;
            if(nullValue != null && nullValue.Equals(fieldValue))
                errorMessage = string.Format("You cannot leave the {0} field empty.", fieldName);
            if(fieldValue == null || string.IsNullOrEmpty(fieldValue.ToString()))
                errorMessage = string.Format("You cannot leave the {0} field empty.", fieldName);
            return errorMessage;
        }
        public static string GetErrorMessage<T>(Expression<Func<T>> expression, object fieldValue, object nullValue = null) {
            string fieldName = BindableBase.GetPropertyName(expression);
            return GetErrorMessage(fieldName, fieldValue, nullValue);
        }

        public string FieldName { get; set; }
        public override ValidationResult Validate(object value, CultureInfo cultureInfo) {
            string error = GetErrorMessage(FieldName, value);
            if(!string.IsNullOrEmpty(error))
                return new ValidationResult(false, error);
            return ValidationResult.ValidResult;
        }
    }
}
RegistrationForm.Lesson5/View/RegistrationView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.RegistrationView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             xmlns:DataModel="clr-namespace:RegistrationForm.DataModel"
             xmlns:dxlc="http://schemas.devexpress.com/winfx/2008/xaml/layoutcontrol" 
             xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" 
             xmlns:sys="clr-namespace:System;assembly=mscorlib"
             mc:Ignorable="d" d:DesignHeight="450" d:DesignWidth="400"
             DataContext="{dxmvvm:ViewModelSource {x:Type ViewModel:RegistrationViewModel}}">
    <UserControl.Resources>
        <Style x:Key="labelStyle" TargetType="dxlc:LayoutItemLabel">
            <Setter Property="FontWeight" Value="Bold"/>
        </Style>
        <Style x:Key="itemStyle" TargetType="dxlc:LayoutItem">
            <Setter Property="LabelPosition" Value="Top"/>
            <Setter Property="LabelStyle" Value="{StaticResource labelStyle}"/>
        </Style>
    </UserControl.Resources>
    <Grid>
        <dxlc:LayoutControl x:Name="container" dxe:ValidationService.IsValidationContainer="True"
                            Orientation="Vertical" ItemStyle="{StaticResource itemStyle}" ItemSpace="10">
            <dxlc:LayoutGroup ItemSpace="10">
                <dxlc:LayoutItem Label="Name">
                    <dxe:TextEdit NullText="FIRST" ValidateOnEnterKeyPressed="True" ValidateOnTextInput="False">
                        <dxe:TextEdit.EditValue>
                            <Binding Path="FirstName" ValidatesOnDataErrors="True"
                                     UpdateSourceTrigger="PropertyChanged" Mode="TwoWay"/>
                        </dxe:TextEdit.EditValue>
                    </dxe:TextEdit>
                </dxlc:LayoutItem>
                <dxe:TextEdit VerticalAlignment="Bottom" NullText="LAST">
                    <dxe:TextEdit.EditValue>
                        <Binding Path="LastName" ValidatesOnDataErrors="True"
                                 UpdateSourceTrigger="PropertyChanged" Mode="TwoWay"/>
                    </dxe:TextEdit.EditValue>
                </dxe:TextEdit>
            </dxlc:LayoutGroup>
            <dxlc:LayoutItem Label="Email">
                <dxe:TextEdit MaskType="RegEx"
                              Mask="[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}"
                              MaskIgnoreBlank="True" InvalidValueBehavior="AllowLeaveEditor">
                    <dxe:TextEdit.EditValue>
                        <Binding Path="Email" ValidatesOnDataErrors="True"
                                 UpdateSourceTrigger="PropertyChanged" Mode="TwoWay"/>
                    </dxe:TextEdit.EditValue>
                </dxe:TextEdit>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Create a password">
                <dxe:PasswordBoxEdit>
                    <dxe:PasswordBoxEdit.EditValue>
                        <Binding Path="Password" ValidatesOnDataErrors="True"
                                 UpdateSourceTrigger="PropertyChanged" Mode="TwoWay"/>
                    </dxe:PasswordBoxEdit.EditValue>
                </dxe:PasswordBoxEdit>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Confirm your password">
                <dxe:PasswordBoxEdit EditValue="{Binding ConfirmPassword, ValidatesOnDataErrors=True}" 
                                     ValidateOnEnterKeyPressed="True" ValidateOnTextInput="True"/>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Birthday">
                <dxe:DateEdit InvalidValueBehavior="AllowLeaveEditor"
                              MinValue="{Binding MinBirthday}" MaxValue="{Binding MaxBirthday}">
                    <dxe:DateEdit.EditValue>
                        <Binding Path="Birthday" ValidatesOnDataErrors="True"
                                 UpdateSourceTrigger="PropertyChanged" Mode="TwoWay"/>
                    </dxe:DateEdit.EditValue>
                    <dxe:DateEdit.StyleSettings>
                        <dxe:DateEditPickerStyleSettings/>
                    </dxe:DateEdit.StyleSettings>
                </dxe:DateEdit>
            </dxlc:LayoutItem>
            <dxlc:LayoutItem Label="Gender">
                <dxe:ComboBoxEdit NullText="I am..."
                                  ItemsSource="{x:Static Member=DataModel:GenderList.Source}" 
                                  ValueMember="ID" DisplayMember="Description">
                    <dxe:ComboBoxEdit.EditValue>
                        <Binding Path="Gender" ValidatesOnDataErrors="True"
                                 UpdateSourceTrigger="PropertyChanged" Mode="TwoWay"/>
                    </dxe:ComboBoxEdit.EditValue>
                    <dxe:ComboBoxEdit.NullValue>
                        <sys:Int32>-1</sys:Int32>
                    </dxe:ComboBoxEdit.NullValue>
                </dxe:ComboBoxEdit>
            </dxlc:LayoutItem>
            <Button Content="Register" HorizontalAlignment="Center" VerticalAlignment="Bottom" Width="80" 
                    Command="{Binding AddEmployeeCommand}" 
                    IsEnabled="{Binding ElementName=container, Path=(dxe:ValidationService.HasValidationError), Converter={dxmvvm:BooleanNegationConverter}}"/>
        </dxlc:LayoutControl>
    </Grid>
</UserControl>
RegistrationForm.Lesson5/ViewModel/RegistrationViewModel.cs 
C#
using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.POCO;
using RegistrationForm.DataModel;
using System;
using System.ComponentModel;
using System.Windows;

namespace RegistrationForm.ViewModel {
    [POCOViewModel]
    public class RegistrationViewModel : IDataErrorInfo {
        public static RegistrationViewModel Create() {
            return ViewModelSource.Create(() => new RegistrationViewModel());
        }
        protected RegistrationViewModel() {
            MinBirthday = new DateTime(DateTime.Now.Year - 100, 12, 31);
            MaxBirthday = new DateTime(DateTime.Now.Year - 1, 12, 31);
            if(this.IsInDesignMode())
                InitializeInDesignMode();
            else InitializeInRuntime();
        }
        void InitializeInDesignMode() {
            FirstName = "John";
            LastName = "Smith";
            Email = "John.Smith@JohnSmithMail.com";
            Password = "Password";
            ConfirmPassword = "Password";
            Birthday = new DateTime(1980, 1, 1);
            Gender = 1;
        }
        void InitializeInRuntime() {
            Birthday = null;
            Gender = -1;
        }

        public virtual string FirstName { get; set; }
        public virtual string LastName { get; set; }
        public virtual string Email { get; set; }
        public virtual string Password { get; set; }
        public virtual string ConfirmPassword { get; set; }
        public virtual DateTime? Birthday { get; set; }
        public virtual DateTime MinBirthday { get; set; }
        public virtual DateTime MaxBirthday { get; set; }
        public virtual int Gender { get; set; }

        public void AddEmployee() {
            string error = EnableValidationAndGetError();
            if(error != null) {
                OnValidationFailed(error);
                return;
            }
            EmployeesModelHelper.AddNewEmployee(FirstName, LastName, Email, Password, Birthday.Value, Gender);
            OnValidationSucceeded();
        }
        protected void OnPasswordChanged() {
            this.RaisePropertyChanged(x => x.ConfirmPassword);
        }
        void OnValidationSucceeded() {
            this.GetService<IMessageBoxService>().Show("Registration succeeded", "Registration Form", MessageBoxButton.OK);
        }
        void OnValidationFailed(string error) {
            this.GetService<IMessageBoxService>().Show("Registration failed. " + error, "Registration Form", MessageBoxButton.OK);
        }

        bool allowValidation = false;
        string EnableValidationAndGetError() {
            allowValidation = true;
            string error = ((IDataErrorInfo)this).Error;
            if(!string.IsNullOrEmpty(error)) {
                this.RaisePropertiesChanged();
                return error;
            }
            return null;
        }
        string IDataErrorInfo.Error {
            get {
                if(!allowValidation) return null;
                IDataErrorInfo me = (IDataErrorInfo)this;
                string error =
                    me[BindableBase.GetPropertyName(() => FirstName)] +
                    me[BindableBase.GetPropertyName(() => LastName)] +
                    me[BindableBase.GetPropertyName(() => Email)] +
                    me[BindableBase.GetPropertyName(() => Password)] +
                    me[BindableBase.GetPropertyName(() => ConfirmPassword)] +
                    me[BindableBase.GetPropertyName(() => Birthday)] +
                    me[BindableBase.GetPropertyName(() => Gender)];
                if(!string.IsNullOrEmpty(error))
                    return "Please check inputted data.";
                return null;
            }
        }
        string IDataErrorInfo.this[string columnName] {
            get {
                if(!allowValidation) return null;
                string firstNameProp = BindableBase.GetPropertyName(() => FirstName);
                string lastNameProp = BindableBase.GetPropertyName(() => LastName);
                string emailProp = BindableBase.GetPropertyName(() => Email);
                string passwordProp = BindableBase.GetPropertyName(() => Password);
                string confirmPasswordProp = BindableBase.GetPropertyName(() => ConfirmPassword);
                string birthdayProp = BindableBase.GetPropertyName(() => Birthday);
                string genderProp = BindableBase.GetPropertyName(() => Gender);
                if (columnName == firstNameProp) {
                    if (FirstName == null || string.IsNullOrEmpty(FirstName))
                        return string.Format("You cannot leave the {0} field empty.", firstNameProp);
                } else if (columnName == lastNameProp) {
                    if (LastName == null || string.IsNullOrEmpty(LastName))
                        return string.Format("You cannot leave the {0} field empty.", lastNameProp);
                } else if (columnName == emailProp) {
                    if (Email == null || string.IsNullOrEmpty(Email))
                        return string.Format("You cannot leave the {0} field empty.", emailProp);
                } else if (columnName == passwordProp) {
                    if (Password == null || string.IsNullOrEmpty(Password))
                        return string.Format("You cannot leave the {0} field empty.", passwordProp);
                } else if (columnName == confirmPasswordProp) {
                    if (!string.IsNullOrEmpty(Password) && Password != ConfirmPassword)
                        return "These passwords do not match. Please try again.";
                } else if (columnName == birthdayProp) {
                    if (Birthday == null || string.IsNullOrEmpty(Birthday.ToString()))
                        return string.Format("You cannot leave the {0} field empty.", birthdayProp);
                } else if (columnName == genderProp) {
                    if (Gender == -1)
                        return string.Format("You cannot leave the {0} field empty.", genderProp);
                }
                return null;
            }
        }
    }
}
RegistrationForm.Lesson5/View/MainView.xaml 
XAML
<UserControl x:Class="RegistrationForm.View.MainView" 
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core"
             xmlns:ViewModel="clr-namespace:RegistrationForm.ViewModel"
             xmlns:View="clr-namespace:RegistrationForm.View"
             mc:Ignorable="d" d:DesignHeight="500" d:DesignWidth="500"
             DataContext="{dxmvvm:ViewModelSource ViewModel:MainViewModel}">
    <dxmvvm:Interaction.Behaviors>
        <dx:DXMessageBoxService/>
    </dxmvvm:Interaction.Behaviors>
    <Grid x:Name="root">
        <dx:DXTabControl TabContentCacheMode="CacheAllTabs">
            <dx:DXTabControl.View>
                <dx:TabControlScrollView HeaderLocation="Bottom" HeaderOrientation="Horizontal" ScrollButtonShowMode="Never"/>
            </dx:DXTabControl.View>
            <dx:DXTabItem Header="Registration Form">
                <View:RegistrationView Width="300" dxmvvm:ViewModelExtensions.ParentViewModel="{Binding ElementName=root, Path=DataContext}"/>
            </dx:DXTabItem>
            <dx:DXTabItem Header="Records">
                <View:RecordsView dxmvvm:ViewModelExtensions.ParentViewModel="{Binding ElementName=root, Path=DataContext}"/>
            </dx:DXTabItem>
        </dx:DXTabControl>
    </Grid>
</UserControl>

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