WPF,MVVM : LostFocus Property for a textbox which should raise a command in ViewModel

Below is my code:

public class TextBoxBehavior
{
public static DependencyProperty OnLostFocusProperty = DependencyProperty.RegisterAttached(
"OnLostFocus",
typeof(ICommand),
typeof(TextBoxBehavior),
new UIPropertyMetadata(TextBoxBehavior.OnLostFocus));

public static void SetOnLostFocus(DependencyObject target, ICommand value)
{
target.SetValue(TextBoxBehavior.OnLostFocusProperty, value);
}

///

/// PropertyChanged callback for OnDoubleClickProperty. Hooks up an event handler with the
/// actual target.
///

private static void OnLostFocus(DependencyObject target, DependencyPropertyChangedEventArgs e)
{
var element = target as TextBox;
if (element == null)
{
throw new InvalidOperationException("This behavior can be attached to a TextBox item only.");
}

if ((e.NewValue != null) && (e.OldValue == null))
{
element.LostFocus += OnPreviewLostFocus;
}
else if ((e.NewValue == null) && (e.OldValue != null))
{
element.LostFocus -= OnPreviewLostFocus;
}
}

private static void OnPreviewLostFocus(object sender, RoutedEventArgs e)
{
UIElement element = (UIElement)sender;
ICommand command = (ICommand)element.GetValue(TextBoxBehavior.OnLostFocusProperty);
if (command != null)
{
command.Execute(e);
}
}
}
---------------
public class Customer : INotifyPropertyChanged
{

public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}

private string name;
public string Name
{
get
{
return name;
}
set
{
name = value;
//RaisePropertyChanged("Name");
}
}

private string country;
public string Country
{
get
{
return country;
}
set
{
country = value;
RaisePropertyChanged("Country");
}
}

private int id;
public int Id
{
get
{
return id;
}
set
{
id = value;
RaisePropertyChanged("Id");
}
}
}

public class MyViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}

private ICommand nameChangeCommand;
public ICommand NameChangeCommand
{
get
{
if (nameChangeCommand == null)
nameChangeCommand = new RelayCommand(ValidateAndChangeName);

return nameChangeCommand;
}

}

private void ValidateAndChangeName(object obj)
{

}

private Customer customer;
public Customer Customer
{
get
{
return customer;
}
set
{
customer = value;
RaisePropertyChanged("Customer");
}
}
}
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