NullReferenceException in Designer due to UserControl [closed]

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Closed 9 years ago.

So I'm trying to make an application with 2 user controls side by side, that slide left and right when you switch between them. The problem is, that one of my user controls (AddReferencePage), when added to the MainWindow, causes the opening tag on my MainWindow to become underlined with a NullReferenceException Error. The designer also shows an error:

NullReferenceException: Object reference not set to an instance of an object.

StackTrace:
 at ARC.AddReferencePage.ReferenceDetails()
at ARC.AddReferencePage.AddReferencePage_Loaded(Object sender, RoutedEventArgs e)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
at System.Windows.BroadcastEventHelper.BroadcastEvent(DependencyObject root, RoutedEvent routedEvent)
at System.Windows.BroadcastEventHelper.BroadcastLoadedEvent(Object root)
at MS.Internal.LoadedOrUnloadedOperation.DoWork()
at System.Windows.Media.MediaContext.FireLoadedPendingCallbacks()
at System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
at System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget)
at System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler

The code to display my user controls is:

<DockPanel x:Name="SlideGrid" VerticalAlignment="Stretch" Width="{Binding ActualWidth, ElementName=MainGrid, Converter={StaticResource DoubleConverter}}" Margin="0,28,0,0" ClipToBounds="True">
    <ItemsControl DockPanel.Dock="Left">
        <local:MainPage/>
    </ItemsControl>
    <ItemsControl DockPanel.Dock="Right">
        <local:AddReferencePage/>
    </ItemsControl>
</DockPanel>

The MainPage works fine, no errors what so ever. Its the AddReferencePage that causes the errors. I have checked through each of the user controls respective code behinds, and they are for all intents and purposes identical.

Code behind for MainPage:

Imports System.Collections.ObjectModel
Imports System.ComponentModel
Imports System.Collections.Specialized
Imports System.Windows.Threading
Imports System.Windows.Media.Animation
Imports System.Globalization

Public Class MainPage
Private StartPoint As Point

Private Sub MainPage_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
    'Dim PW As MainWindow = Window.GetWindow(MainPage)
    'If PW IsNot Nothing Then
    '    ReferenceList.ItemsSource = PW.ReferenceCollection
    '    Dim Alphabetical As SortDescription = New SortDescription("PropLastName", ListSortDirection.Ascending)
    '    ReferenceList.Items.SortDescriptions.Add(Alphabetical)
    'End If
    RefreshReferences()
End Sub

Public Sub RefreshReferences()
    Dim PW As MainWindow = Window.GetWindow(MainPage)
    If PW IsNot Nothing Then
        ReferenceList.ItemsSource = PW.ReferenceCollection
        Dim Alphabetical As SortDescription = New SortDescription("PropLastName", ListSortDirection.Ascending)
        ReferenceList.Items.SortDescriptions.Add(Alphabetical)
    End If
End Sub

Private Sub ListBoxSearch_TextChanged(sender As Object, e As TextChangedEventArgs) Handles ListBoxSearch.TextChanged
    If ListBoxSearch.Text <> "Search..." Then
        Dim PW As MainWindow = Window.GetWindow(MainPage)
        If PW IsNot Nothing Then
            PW.view = CollectionViewSource.GetDefaultView(PW.ReferenceCollection)
            PW.view.Filter = New Predicate(Of Object)(AddressOf PW.FilterList)
        End If
    End If

End Sub

Private Sub ListBoxSearch_MouseLeftButtonUp(sender As Object, e As MouseButtonEventArgs) Handles ListBoxSearch.PreviewMouseDown
    If ListBoxSearch.Text = "Search..." Then
        ListBoxSearch.FontStyle = FontStyles.Normal
        ListBoxSearch.Clear()
    End If
End Sub


Private Sub ListBoxSearch_LostFocus(sender As Object, e As RoutedEventArgs) Handles ListBoxSearch.LostFocus
    If ListBoxSearch.Text = "" Then
        ListBoxSearch.FontStyle = FontStyles.Italic
        ListBoxSearch.Text = "Search..."
    End If
End Sub

Private Sub ListViewClick(sender As Object, e As RoutedEventArgs) Handles ButtonListView.Click
    If ReferenceList.ItemTemplate Is FindResource("GridViewTemplate") Then
        ViewBackground.BeginStoryboard(DirectCast(Me.Resources("ViewRightToLeft"), Storyboard))
        ReferenceList.ItemTemplate = DirectCast(Me.FindResource("ListViewTemplate"), DataTemplate)
        ButtonListView.Content = FindResource("NoListView")
        ButtonGridView.Content = FindResource("NoGridView")
    End If
End Sub

Private Sub GridViewClick(sender As Object, e As RoutedEventArgs) Handles ButtonGridView.Click
    If ReferenceList.ItemTemplate Is FindResource("ListViewTemplate") Then
        ViewBackground.BeginStoryboard(DirectCast(Me.Resources("ViewLeftToRight"), Storyboard))
        ReferenceList.ItemTemplate = DirectCast(Me.FindResource("GridViewTemplate"), DataTemplate)
        ButtonListView.Content = FindResource("NoListView")
        ButtonGridView.Content = FindResource("NoGridView")
    End If
End Sub

Private Sub ListViewEnter(sender As Object, e As RoutedEventArgs) Handles ButtonListView.MouseEnter

End Sub

Private Sub GridViewEnter(sender As Object, e As RoutedEventArgs) Handles ButtonGridView.MouseEnter

End Sub

Private Sub ListViewLeave(sender As Object, e As RoutedEventArgs) Handles ButtonListView.MouseLeave

End Sub

Private Sub GridViewLeave(sender As Object, e As RoutedEventArgs) Handles ButtonGridView.MouseLeave

End Sub

Private Sub EditListBoxItem(sender As Object, e As RoutedEventArgs)
    Dim PW As MainWindow = Window.GetWindow(MainPage)
    If PW IsNot Nothing Then
        PW.ChangeSlide(sender, 1)
        PW.EditItem = ReferenceList.SelectedItem
        PW.NewItem = False
    End If
End Sub

Private Sub DeleteListBoxItem(sender As Object, e As RoutedEventArgs)
    Dim PW As MainWindow = Window.GetWindow(MainPage)
    If PW IsNot Nothing Then
        PW.ReferenceCollection.Remove(ReferenceList.SelectedItem)
    End If
End Sub

Private Sub NewListBoxItem(sender As Object, e As RoutedEventArgs)
    Dim PW As MainWindow = Window.GetWindow(MainPage)
    If PW IsNot Nothing Then
        PW.ChangeSlide(sender, 1)
        PW.NewItem = True
    End If
End Sub

Private Sub ReferenceList_Loaded(sender As Object, e As RoutedEventArgs) Handles ReferenceList.Loaded
    RefreshReferences()
End Sub

Private Sub ReferenceList_PreviewMouseLeftButtonDown(sender As Object, e As MouseButtonEventArgs) Handles ReferenceList.PreviewMouseLeftButtonDown
    Dim PW As MainWindow = Window.GetWindow(MainPage)
    StartPoint = e.GetPosition(Nothing)
    PW.Resizing = False
End Sub

Private Sub ReferenceList_PreviewMouseMove(sender As Object, e As MouseEventArgs) Handles ReferenceList.PreviewMouseMove
    Dim PW As MainWindow = Window.GetWindow(MainPage)
    If PW.Resizing = False Then
        Dim MousePosition As Point = e.GetPosition(Nothing)
        Dim Difference As Vector = StartPoint - MousePosition
        Dim StopDrop As Boolean
        If e.LeftButton = MouseButtonState.Pressed AndAlso (Math.Abs(Difference.X) > SystemParameters.MinimumHorizontalDragDistance Or Math.Abs(Difference.Y) > SystemParameters.MinimumVerticalDragDistance) Then
            Dim LB As ListBox = sender
            Dim UIE As UIElement = LB.InputHitTest(MousePosition)
            If UIE IsNot Nothing Then
                Dim Data As Object = DependencyProperty.UnsetValue
                While Data Is DependencyProperty.UnsetValue And UIE IsNot Nothing
                    Data = LB.ItemContainerGenerator.ItemFromContainer(UIE)
                    If Data Is DependencyProperty.UnsetValue Then
                        UIE = VisualTreeHelper.GetParent(UIE)
                    End If
                    If UIE Is LB Then
                        StopDrop = True
                    End If
                End While
                If Data IsNot DependencyProperty.UnsetValue Then
                    StopDrop = False
                End If
            Else
                StopDrop = True
            End If
            PW.TempItem = LB.SelectedItem
            Dim FN As String = PW.TempItem.PropLastName & ", " & PW.TempItem.PropFirstName.Substring(0, 1)
            Dim TT As String = PW.TempItem.PropTitle
            Dim YR As String = PW.TempItem.PropYear.ToString
            Dim ReferenceText As String = FN & " " & YR & ", " & TT
            Dim DragData As DataObject = New DataObject(DataFormats.StringFormat, ReferenceText)
            If DragData IsNot Nothing And StopDrop = False Then
                DragDrop.DoDragDrop(sender, DragData, DragDropEffects.Copy)
            End If
        End If
    End If

End Sub
End Class

XAML for MainPage:

<UserControl x:Class="MainPage" x:Name="MainPage"
         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:ARC"
         mc:Ignorable="d"
         VerticalAlignment="Stretch" HorizontalAlignment="Stretch" d:DesignWidth="400" d:DesignHeight="600" SnapsToDevicePixels="True">
<UserControl.Resources>
    <local:ImageConverter x:Key="ImageConverter"/>
    <Image x:Key="BrownBook" Source="Images\Icons\BrownBook.png" Height="64" Width="64"/>

    <Storyboard x:Key="ViewRightToLeft" 
                AccelerationRatio=".5"
                DecelerationRatio=".5">
        <ThicknessAnimation Storyboard.TargetName="ViewBackground" Storyboard.TargetProperty="Margin" Duration="0:0:0.15" To="0,0,28,0"/>
    </Storyboard>

    <Storyboard x:Key="ViewLeftToRight" 
                AccelerationRatio=".5"
                DecelerationRatio=".5">
        <ThicknessAnimation Storyboard.TargetName="ViewBackground" Storyboard.TargetProperty="Margin" Duration="0:0:0.15" To="0,0,-28,0"/>
    </Storyboard>
</UserControl.Resources>

<Grid Background="#FFF1F1F1">
    <Grid>
        <DockPanel VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
            <DockPanel Margin="0,0,0,0" VerticalAlignment="Top" HorizontalAlignment="Stretch" Height="28" DockPanel.Dock="Top" Background="#E5E5E5">
                <Button BorderThickness="0" x:Name="AddNewReference" Style="{DynamicResource NoChromeButton}" DockPanel.Dock="Right" HorizontalAlignment="Right" Click="ListViewClick" Height="28" Width="28">
                    <DynamicResource ResourceKey="SearchBar"/>
                </Button>
                <Button BorderThickness="0" x:Name="Settings" Style="{DynamicResource NoChromeButton}" DockPanel.Dock="Right" HorizontalAlignment="Right" Click="ListViewClick" Height="28" Width="28">
                    <DynamicResource ResourceKey="SearchBar"/>
                </Button>
                <Grid Margin="0,0,0,0" DockPanel.Dock="Right" Width="56" Height="28" VerticalAlignment="Top" HorizontalAlignment="Stretch">
                    <Button Height="28" Width="28" Margin="0,0,28,0" BorderThickness="0" Style="{DynamicResource NoChromeButton}" x:Name="ViewBackground" Background="#3E3B3B"/>
                    <Button Margin="0,0,0,0" BorderThickness="0" x:Name="ButtonGridView" Style="{DynamicResource NoChromeButton}" HorizontalAlignment="Right" Click="GridViewClick" Height="28" Width="28">
                        <DynamicResource ResourceKey="NoGridView"/>
                    </Button>
                    <Button Margin="0,0,28,0" BorderThickness="0" x:Name="ButtonListView" Style="{DynamicResource NoChromeButton}" HorizontalAlignment="Right" Click="ListViewClick" Height="28" Width="28">
                        <DynamicResource ResourceKey="NoListView"/>
                    </Button>

                </Grid>
                <Button BorderThickness="0" x:Name="SearchBarIcon" Style="{DynamicResource NoChromeButton}" DockPanel.Dock="Left" HorizontalAlignment="Right" Click="ListViewClick" Height="28" Width="23">
                    <DynamicResource ResourceKey="SearchBar"/>
                </Button>
                <TextBox x:Name="ListBoxSearch" Style="{DynamicResource SearchBoxTemplate}" Text="Search..." FontSize="16" HorizontalAlignment="Stretch" FontStyle="Italic" BorderThickness="0" Foreground="Gray" Background="Transparent" VerticalContentAlignment="Top"/>

            </DockPanel>
            <ListBox AlternationCount="2"  DockPanel.Dock="Top" Margin="0,0,0,0" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding ReferenceCollection, ElementName=local:MainWindow}" TextSearch.TextPath="SearchString" x:Name="ReferenceList" HorizontalContentAlignment="Stretch" ScrollViewer.CanContentScroll="False" SnapsToDevicePixels="True" AllowDrop="True" BorderThickness="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
                <ListBox.Background>
                    <LinearGradientBrush StartPoint="1,1" EndPoint="1,0">
                        <GradientStop Offset="0.0" Color="#190000FF"/>
                        <GradientStop Color="#000000FF" Offset="1.0"/>
                    </LinearGradientBrush>
                </ListBox.Background>
                <ListBox.ItemTemplate>
                        <StaticResource ResourceKey="ListViewTemplate"/>
                </ListBox.ItemTemplate>
                <ListBox.ContextMenu>
                    <ContextMenu Style="{StaticResource ListBoxContextMenu}">
                        <MenuItem x:Name="EditContextMenuItem" Header="Edit" Click="EditListBoxItem" Style="{StaticResource ListBoxContextMenuItem}"/>
                        <MenuItem x:Name="DeleteContextMenuItem" Header="Delete" Click="DeleteListBoxItem" Style="{StaticResource ListBoxContextMenuItem}"/>
                        <MenuItem x:Name="NewContextMenuItem" Header="New" Click="NewListBoxItem" Style="{StaticResource ListBoxContextMenuItem}"/>
                    </ContextMenu>
                </ListBox.ContextMenu>
            </ListBox>
        </DockPanel>
    </Grid>
</Grid>
</UserControl>

Code behind for AddReferencePage:

Imports System.Collections.ObjectModel
Imports System.ComponentModel
Imports System.Collections.Specialized
Imports System.Windows.Threading
Imports System.Windows.Media.Animation
Imports System.Globalization

Public Class AddReferencePage
Private SelectImage As Boolean = False

Private Sub ReturnToReferences(sender As Object, e As RoutedEventArgs)
    Dim PW As MainWindow = Window.GetWindow(AddReferencePage)
    If PW IsNot Nothing Then
        If ReferenceAuthor.Text <> "Author" Or ReferenceDate.Text <> "Date" Or ReferenceTitle.Text <> "Title" Then
            Dim CN As String() = Nothing
            Dim FN As String = Nothing
            Dim LN As String = Nothing
            Dim YR As String = Nothing
            Dim TT As String = Nothing

            If ReferenceAuthor.Text = "Author" Then
                ReferenceAuthor.Text = "Unknown"
                FN = Nothing
                LN = "Unknown"
            Else
                If ReferenceAuthor.Text.Contains(" ") Then
                    CN = ReferenceAuthor.Text.Split(" ")
                    FN = CN.First
                    LN = CN.Last
                Else
                    FN = Nothing
                    LN = ReferenceAuthor.Text
                End If

            End If
            If ReferenceDate.Text = "Date" Then
                ReferenceDate.Text = "Unknown"
                YR = "Unknown"
            Else
                YR = ReferenceDate.Text
            End If
            If ReferenceTitle.Text = "Title" Then
                ReferenceTitle.Text = "Unknown"
                TT = "Unknown"
            Else
                TT = ReferenceTitle.Text
            End If
            If PW.NewItem = False Then
                PW.ReferenceCollection.Remove(PW.EditItem)
                PW.AddReferenceItem(FN, LN, TT, YR, "Book")
            Else
                PW.AddReferenceItem(FN, LN, TT, YR, "Book")
            End If
        End If
    End If
    PW.ChangeSlide(sender, 0)
End Sub

Private Sub ButtonsMouseEnter(sender As Button, e As RoutedEventArgs)
    Select Case sender.Name
        Case "ReturnReferences"
            sender.Content = FindResource("BackArrowHover")
    End Select
End Sub

Private Sub ButtonsMouseLeave(sender As Button, e As RoutedEventArgs)
    Select Case sender.Name
        Case "ReturnReferences"
            sender.Content = FindResource("BackArrowNormal")
    End Select
End Sub

Private Sub ButtonsMouseDown(sender As Button, e As RoutedEventArgs)
    Select Case sender.Name
        Case "ReturnReferences"
            sender.Content = FindResource("BackArrowClick")
    End Select
End Sub

Public Sub SaveReferenceSub(sender As Object, e As RoutedEventArgs)
    Dim PW As MainWindow = Window.GetWindow(AddReferencePage)
    Dim CN As String() = ReferenceAuthor.Text.Split(" ")
    Dim FN As String = CN.First()
    Dim LN As String = CN.Last()
    Dim YR As Integer = CInt(ReferenceDate.Text)
    Dim TT As String = ReferenceTitle.Text
    If PW.NewItem = False Then
        PW.ReferenceCollection.Remove(PW.EditItem)
        PW.AddReferenceItem(FN, LN, TT, YR, "Book")
    Else
        PW.AddReferenceItem(FN, LN, TT, YR, "Book")
    End If
End Sub

Private Sub ReferenceDetails()
    Dim PW As MainWindow = Window.GetWindow(AddReferencePage)
    If PW.NewItem = False Then
        ReferenceAuthor.Text = PW.EditItem.PropFirstName & " " & PW.EditItem.PropLastName
        ReferenceTitle.Text = PW.EditItem.PropTitle
        ReferenceDate.Text = PW.EditItem.PropYear.ToString
    End If
End Sub

Private Sub AddReferencePage_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
    ReferenceDetails()
End Sub

Private Sub FieldEnter(sender As TextBox, e As RoutedEventArgs)
    Select Case sender.Name
        Case "ReferenceAuthor"
            If sender.Text = "Author" Then
                sender.Clear()
            End If
        Case "ReferenceTitle"
            If sender.Text = "Title" Then
                sender.Clear()
            End If
        Case "ReferenceDate"
            If sender.Text = "Date" Then
                sender.Clear()
            End If
    End Select
End Sub

Private Sub FieldLeave(sender As TextBox, e As RoutedEventArgs)
    If sender.Text = "" Then
        Select Case sender.Name
            Case "ReferenceAuthor"
                sender.Text = "Author"
            Case "ReferenceTitle"
                sender.Text = "Title"
            Case "ReferenceDate"
                sender.Text = "Date"
        End Select
    End If
End Sub

Private Sub FieldChanged(sender As TextBox, e As RoutedEventArgs)
    If sender.Text <> "Author" And sender.Text <> "Date" And sender.Text <> "Title" Then
        sender.Foreground = Brushes.Black
    Else
        sender.Foreground = Brushes.Gray
    End If
End Sub

Private Sub Button_Click_1(sender As Object, e As RoutedEventArgs)
    If SelectImage = False Then
        SelectImageBox.BeginStoryboard(DirectCast(Me.Resources("LeftToRight"), Storyboard))
        SelectImage = True
    Else
        SelectImageBox.BeginStoryboard(DirectCast(Me.Resources("RightToLeft"), Storyboard))
        SelectImage = False
    End If
End Sub

Private Sub SelectImageBox_LostFocus(sender As Object, e As RoutedEventArgs) Handles SelectImageBox.LostFocus
    'If SelectImage = True Then
    '    SelectImageBox.BeginStoryboard(DirectCast(Me.Resources("RightToLeft"), Storyboard))
    '    SelectImage = False
    'End If
End Sub
End Class

XAML for AddReferencePage:

<UserControl x:Class="AddReferencePage" x:Name="AddReferencePage"
         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:ARC"
         mc:Ignorable="d"
         VerticalAlignment="Stretch" SnapsToDevicePixels="True" HorizontalAlignment="Stretch" d:DesignWidth="400" d:DesignHeight="600">
<UserControl.Resources>
    <Storyboard x:Key="RightToLeft" 
                AccelerationRatio=".5"
                DecelerationRatio=".5">
        <DoubleAnimation Storyboard.TargetName="ReferenceInfo" Storyboard.TargetProperty="(Canvas.Left)" Duration="0:0:0.3" To="0"/>
        <DoubleAnimation Storyboard.TargetName="SelectImageBox" Storyboard.TargetProperty="Opacity" Duration="0:0:0.3" From="1.0" To="0.0"/>
    </Storyboard>

    <Storyboard x:Key="LeftToRight" 
                AccelerationRatio=".5"
                DecelerationRatio=".5">
        <DoubleAnimation Storyboard.TargetName="ReferenceInfo" Storyboard.TargetProperty="(Canvas.Left)" Duration="0:0:0.3" To="{Binding ActualWidth, ElementName=AnimInfo}"/>
        <DoubleAnimation Storyboard.TargetName="SelectImageBox" Storyboard.TargetProperty="Opacity" Duration="0:0:0.3" From="0.0" To="1.0"/>
    </Storyboard>
</UserControl.Resources>


<Grid Background="#FFF1F1F1">
    <Button Style="{DynamicResource NoChromeButton}" x:Name="ReturnReferences" Click="ReturnToReferences" MouseDown="ButtonsMouseDown" MouseEnter="ButtonsMouseEnter" MouseLeave="ButtonsMouseLeave" VerticalAlignment="Top" HorizontalAlignment="Left" Margin="5,5,0,0" Height="48" Width="48">
        <DynamicResource ResourceKey="BackArrowNormal"/>
    </Button>

    <TextBlock Text="Edit References" FontFamily="Segoe UI Light" FontSize="36" Margin="72,3,0,0" VerticalAlignment="Top" HorizontalAlignment="Stretch"/>
    <TextBlock x:Name="AnimInfo" FontFamily="Segoe UI Light" FontSize="36" Margin="72,3,60,0" VerticalAlignment="Top" HorizontalAlignment="Stretch"/>
    <ListView x:Name="SelectImageBox" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" Margin="72,59,60,20" Background="Transparent" ScrollViewer.HorizontalScrollBarVisibility="Disabled" BorderThickness="0" Opacity="0">
        <ListView.ItemsPanel>
            <ItemsPanelTemplate>
                <WrapPanel Orientation="Horizontal" IsItemsHost="True"/>
            </ItemsPanelTemplate>
        </ListView.ItemsPanel>
        <Button Style="{DynamicResource NoChromeButton}" Height="48" Width="48">
            <DynamicResource ResourceKey="Book"/>
        </Button>
        <Button Style="{DynamicResource NoChromeButton}" Height="48" Width="48">
            <DynamicResource ResourceKey="Book"/>
        </Button>
        <Button Style="{DynamicResource NoChromeButton}" Height="48" Width="48">
            <DynamicResource ResourceKey="Book"/>
        </Button>
        <Button Style="{DynamicResource NoChromeButton}" Height="48" Width="48">
            <DynamicResource ResourceKey="Book"/>
        </Button>
        <Button Style="{DynamicResource NoChromeButton}" Height="48" Width="48">
            <DynamicResource ResourceKey="Book"/>
        </Button>
        <Button Style="{DynamicResource NoChromeButton}" Height="48" Width="48">
            <DynamicResource ResourceKey="Book"/>
        </Button>
    </ListView>
    <Canvas x:Name="InfoCanvas" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" Margin="72,60,0,0" Opacity="1">
        <DockPanel VerticalAlignment="Stretch" HorizontalAlignment="Stretch" Margin="0,0,0,0" x:Name="ReferenceInfo" Canvas.Left="0" Canvas.Top="0" Width="{Binding ActualWidth, ElementName=InfoCanvas}" Height="{Binding ActualHeight, ElementName=InfoCanvas}">
            <TextBox x:Name="ReferenceAuthor" GotFocus="FieldEnter" TextChanged="FieldChanged" LostFocus="FieldLeave" FontSize="16" FontFamily="Segoe UI Light" Text="Author" Foreground="Gray" Background="Transparent" DockPanel.Dock="Top" VerticalAlignment="Top" HorizontalAlignment="Stretch" BorderThickness="0" Margin="0,2,0,2"/>
            <TextBox x:Name="ReferenceTitle" GotFocus="FieldEnter" TextChanged="FieldChanged" LostFocus="FieldLeave" FontSize="16" FontFamily="Segoe UI Light" Text="Title" Foreground="Gray" Background="Transparent" DockPanel.Dock="Top" VerticalAlignment="Top" HorizontalAlignment="Stretch" BorderThickness="0" Margin="0,2,0,2"/>
            <TextBox x:Name="ReferenceDate" GotFocus="FieldEnter" TextChanged="FieldChanged" LostFocus="FieldLeave" FontSize="16" FontFamily="Segoe UI Light" Text="Date" Foreground="Gray" Background="Transparent" DockPanel.Dock="Top" VerticalAlignment="Top" HorizontalAlignment="Stretch" BorderThickness="0" Margin="0,2,0,2"/>
        </DockPanel>
    </Canvas>
    <Button Style="{DynamicResource NoChromeButton}" Margin="5,60,0,0" VerticalAlignment="Top" HorizontalAlignment="Left" Width="48" Height="48" VerticalContentAlignment="Center" Click="Button_Click_1">
        <DynamicResource ResourceKey="Book"/>
    </Button>
</Grid>
</UserControl>

I know its a lot of code :D but I really need to fix this problem! Thanks all! Let me know if you need more details. All my resources and templates are defined in Application.xaml which I have not included, due to the irrelevance. I can include if needed.

Answer 1

According to the error stack trace, the error occurs in the sub ReferenceDetails(), which is in your second to last code block in the question. I think the error exists in these lines of code,

Dim PW As MainWindow = Window.GetWindow(AddReferencePage)
    If PW.NewItem = False Then

I haven't worked with WPF, only Winforms. But if the designers are similar, its possible that MainWindow could be Nothing at design time. You could try something like this and see if it fixes the error.

Dim PW As MainWindow = Window.GetWindow(AddReferencePage)
    If PW IsNot Nothing AndAlso PW.NewItem = False Then

That way if PW comes back as Nothing it won't cause a NullReferenceException. Also (again I assume WPF designers work similar to Winfors), be sure to rebuild after changing the code, before you try adding it to the main window again.

Answer 2

Thanks to Kratz for responding so quickly. After a little bit more playing around, I figured out that I needed to put the user controls inside a Frame. :D