Usercontrol within Usercontrol with Data Binding - wpf

Question

I built a simple WPF UserControl that I want to implement several of in another UserControl while maintaining the data binding. I have a simple Debug1 window that implements (1) a bound textblock (to verify data binding only) & button; (2) a single instance of the NumericUpDownBox usercontrol with binding; and (3) an instance of the parent user control containing an instance of the child user control NumericUpDownBox.
Items (1) and (2) are working. Item (3) does not. I feel like I am missing something in the implementation in the parent user control code? I also get a couple of errors that concern me (see below).
Debug1 Window xaml:
<Window x:Class="Debug1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:CFIT"
mc:Ignorable="d"
Title="Debug1" Height="225" Width="600"
Closing="ClosingDebug1">
<Grid>
<StackPanel Grid.Row="0" Orientation="Horizontal">
<Button Name="NextButton" Content="Next" Click="ClickNext" Width="50" />
<TextBox Text="{Binding Path=Years, Mode=TwoWay}" />
</StackPanel>
<local:NumericUpDownBox Grid.Row="1" x:Name="SingleBox" Label="TBD" Increment="2" Value="{Binding Path=Years}"/>
<local:YMDH_TimeControl Grid.Row="2" x:Name="TimeControl" YearsValue="{Binding Path=Years}" />
</Grid>
</Window>
Debug Window VB Code:
Public Class Debug1
Public Mat As New clsMaterial
Sub New() ' Removed for brevity
End Sub
Private Sub ClickNext(sender As Object, e As RoutedEventArgs)
Mat.Lives(0).MSDateOffset.Years = Mat.Lives(0).MSDateOffset.Years + 5
End Sub
End Class
Parent UserControl xaml:
<UserControl x:Class="YMDH_TimeControl"
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:local="clr-namespace:CFIT"
mc:Ignorable="d"
d:DesignHeight="50" d:DesignWidth="200" MinHeight="30" MinWidth="160"
Name="YMDH_TimeControl">
<Grid DataContext="{Binding ElementName=YMDH_TimeControl}">
<local:NumericUpDownBox Grid.Column="0" x:Name="Years"/>
</Grid>
</UserControl>
Parent UserControl VB Code:
Public Class YMDH_TimeControl
Public Shared ReadOnly YearsValueProperty As DependencyProperty = DependencyProperty.Register("YearsValue", GetType(Integer), GetType(YMDH_TimeControl), New FrameworkPropertyMetadata(0, (FrameworkPropertyMetadataOptions.BindsTwoWayByDefault), Nothing, New CoerceValueCallback(AddressOf OnValueChanged)))
Private Shared Function OnValueChanged(d As DependencyObject, value As Object) As Object
If IsNumeric(value) Then
Return CInt(value)
Else
Return Nothing
End If
End Function
Public Property YearsValue As Integer
Get
Return Years.Value
End Get
Set(value As Integer)
Years.Value = value
End Set
End Property
End Class
Child UserControl xaml:
<UserControl x:Class="NumericUpDownBox"
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:local="clr-namespace:CFIT"
mc:Ignorable="d"
d:DesignHeight="50" d:DesignWidth="50" MinHeight="30" MinWidth="40"
Name="NumericUpDownBox">
<Grid DataContext="{Binding ElementName=NumericUpDownBox}">
<Grid.Resources>
... removed for brevity...
</Grid.Resources>
<!--Box Definition-->
<Border Style="{StaticResource SectionNameBorder}" Grid.Column="0">
<Grid Background="Gray" >
<Viewbox>
<TextBlock Name="LabelTextBlock" Text="{Binding Path=Label, ElementName=NumericUpDownBox}" VerticalAlignment="Center" HorizontalAlignment="Center"/>
</Viewbox>
<Grid Grid.Row="2" Background="White" >
<Grid Grid.Column="0" HorizontalAlignment="Right">
<Viewbox>
<TextBox Name="ValueTextBox" BorderBrush="White" Text="{Binding Path=Value, Mode=TwoWay, ElementName=NumericUpDownBox, UpdateSourceTrigger=PropertyChanged}" />
</Viewbox>
</Grid>
<Grid Grid.Column="1">
<RepeatButton Name="UpArrow" Style="{StaticResource UpArrowStyle}" Tag="+" Click="TickValues" />
<RepeatButton Name="DownArrow" Style="{StaticResource DownArrowStyle}" Tag="-" Click="TickValues" />
</Grid>
</Grid>
</Grid>
</Border>
</Grid>
</UserControl>
Child UserControl VB Code:
Public Class NumericUpDownBox
Private Const DefaultInc As Integer = 1
Public Sub New()
InitializeComponent()
If Increment = 0 Then Increment = DefaultInc
End Sub
Private Sub TickValues(sender As Object, e As RoutedEventArgs)
Dim Sign As Char
Dim Tag As String
Tag = sender.tag.ToString
If Len(Tag) = 0 Then Exit Sub
Sign = Left(Tag, 1)
If Sign = "+" Then
Value = Value + Increment
ElseIf Sign = "-" Then
Value = Value - Increment
End If
End Sub
Public Property Value As Integer
Get
Return CInt(GetValue(ValueProperty))
End Get
Set(value As Integer)
If value < 0 Then value = 0
SetValue(ValueProperty, value)
End Set
End Property
Public Property Label As String
Get
Return GetValue(LabelProperty)
End Get
Set(value As String)
SetValue(LabelProperty, value)
End Set
End Property
Public Property Increment As Integer
Get
Return CInt(GetValue(IncProperty))
End Get
Set(value As Integer)
If value < 0 Then value = 0
SetValue(IncProperty, value)
End Set
End Property
Public Shared ReadOnly ValueProperty As DependencyProperty = DependencyProperty.Register("Value", GetType(Integer), GetType(NumericUpDownBox), New FrameworkPropertyMetadata(0, (FrameworkPropertyMetadataOptions.BindsTwoWayByDefault), Nothing, New CoerceValueCallback(AddressOf OnValueChanged)))
Public Shared ReadOnly LabelProperty As DependencyProperty = DependencyProperty.Register("Label", GetType(String), GetType(NumericUpDownBox), New FrameworkPropertyMetadata(""))
Public Shared ReadOnly IncProperty As DependencyProperty = DependencyProperty.Register("Increment", GetType(Integer), GetType(NumericUpDownBox), New FrameworkPropertyMetadata(0, Nothing, New CoerceValueCallback(AddressOf OnValueChanged)))
Private Shared Function OnValueChanged(d As DependencyObject, value As Object) As Object
If IsNumeric(value) Then
Return CInt(value)
Else
Return Nothing
End If
End Function
End Class
Example Information Error in the Output Window:
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=Years; DataItem=null; target element is 'YMDH_TimeControl' (Name='TimeControl'); target property is 'YearsValue' (type 'Int32')
How do I get my data binding to pass through my parent user control?