<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1"
    Title="Window1" Height="138" Width="233" _
      xmlns:my="http://schemas.microsoft.com/wpf/2008/toolkit">
    <Window.Resources>
        <local:DateStringConverter _
          x:Key="DateStringConv"></local:DateStringConverter>
    </Window.Resources>
    <Grid>
        <my:DatePicker Text="{Binding TestDate, Mode=TwoWay," & _
          "Converter={StaticResource DateStringConv}," & _
          "RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type" & _
          "Window}}}"  Height="28" Margin="12,12,12,0" Name="DatePicker1" _
          VerticalAlignment="Top" />
        <Button Height="23" Name="Button1" VerticalAlignment="Bottom" _
        Margin="71,0,65,12">Clear</Button>
    </Grid>
</Window>

Imports System.ComponentModel
 
Class Window1
    Implements INotifyPropertyChanged
 
    Public Event PropertyChanged(ByVal sender As Object, ByVal e As _
      System.ComponentModel.PropertyChangedEventArgs) Implements _
      System.ComponentModel.INotifyPropertyChanged.PropertyChanged
 
    Private mTestDate As Date = Date.Now
 
    Public Property TestDate() As Date
        Get
            Return mTestDate
        End Get
        Set(ByVal value As Date)
            mTestDate = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs( _
              "TestDate"))
            Debug.WriteLine(value.ToShortDateString)
        End Set
    End Property
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.Windows.RoutedEventArgs) Handles Button1.Click
        TestDate = #12:00:00 AM#
    End Sub
 
End Class

<ValueConversion(GetType(Date), GetType(String))> _
 Public Class DateStringConverter
    Implements IValueConverter
 
    Public Function Convert(ByVal value As Object, ByVal targetType As _
      System.Type, ByVal parameter As Object, ByVal culture As _
      System.Globalization.CultureInfo) As Object Implements _
      System.Windows.Data.IValueConverter.Convert
        Try
            Dim d As Date = CDate(value)
            If d > #12:00:00 AM# Then
                Return d.ToString
            Else
                Return ""
            End If
        Catch ex As Exception
            Return ""
        End Try
    End Function
 
    Public Function ConvertBack(ByVal value As Object, ByVal targetType As _
      System.Type, ByVal parameter As Object, ByVal culture As _
      System.Globalization.CultureInfo) As Object Implements _
      System.Windows.Data.IValueConverter.ConvertBack
        Dim d As Date
        Date.TryParse(value.ToString, d)
        Return d
    End Function
End Class