<Grid>
  <Grid.RowDefinitions>
    <RowDefinition Height="Auto"/>
    <RowDefinition Height="Auto"/>
    <RowDefinition Height="Auto"/>
  </Grid.RowDefinitions>

  <TextBlock Text="CheckBox Demonstration" Margin="0,20,10,20"
             FontFamily="Verdana" FontSize="18" FontWeight="Bold"
             Foreground="#FF5C9AC9" Grid.Row="0"/>

  <CheckBox x:Name="cb1" Grid.Row="1" Margin="5,0,0,0" 
            Content="Three-state CheckBox" IsThreeState="True"
            Checked="HandleCheck" Unchecked="HandleUnchecked" 
            Indeterminate="HandleThirdState" />
  <TextBlock x:Name="text1" Grid.Row="2" Margin="5,0,0,0" />
</Grid>

Private Sub HandleCheck(ByVal sender As Object, ByVal e As RoutedEventArgs)
    text1.Text = "The CheckBox is checked."
End Sub

Private Sub HandleUnchecked(ByVal sender As Object, ByVal e As RoutedEventArgs)
    text1.Text = "The CheckBox is unchecked."
End Sub

Private Sub HandleThirdState(ByVal sender As Object, ByVal e As RoutedEventArgs)
    text1.Text = "The CheckBox is in the indeterminate state."
End Sub

private void HandleCheck(object sender, RoutedEventArgs e)
{
    text1.Text = "The CheckBox is checked.";
}

private void HandleUnchecked(object sender, RoutedEventArgs e)
{
    text1.Text = "The CheckBox is unchecked.";
}

private void HandleThirdState(object sender, RoutedEventArgs e)
{
    text1.Text = "The CheckBox is in the indeterminate state.";
}