Question

I have a WPF Window that has a custom border, Thumb controls for resizing, and a two-column layout. The right column (main content area) is a UserControl with a ScrollViewer, so it scrolls as needed. I want to add a ScrollViewer to the left column, but when I do, at runtime it gives me

Initialization of ‘System.Windows.Controls.Primitives.ScrollBar’ threw an exception.

with an inner exception of

Unable to cast object of type ‘MS.Internal.NamedObject’ to type ‘System.Windows.FrameworkTemplate’.

If I take the ScrollViewer out, everything works fine again.

Here’s the basic XAML (with the ScrollViewer wrapped around the TaskPane ItemsControl):

<Window x:Class="MyWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Width="525" MinWidth="200"
    Height="350" MinHeight="85"
    FontFamily="Segoe UI"
    AllowsTransparency="True" Background="Transparent" 
    ResizeMode="CanResize" WindowStyle="None">

<Border>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="6"/>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="6"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="6"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="6"/>
        </Grid.RowDefinitions>

        <Grid Grid.Column="1" Grid.Row="1">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="*"/>
                <RowDefinition Height="22"/>
            </Grid.RowDefinitions>

            <Grid Grid.Row="0">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*"/>
                    <ColumnDefinition Width="Auto"/>
                </Grid.ColumnDefinitions>

                <StackPanel Grid.Column="0" Orientation="Vertical">
                    <TextBlock Name="Caption" Text="My Window"/>
                </StackPanel>

                <StackPanel Grid.Column="1" Orientation="Vertical">
                    <!-- Minimize/Maximize/Close buttons -->
                </StackPanel>
            </Grid>

            <Grid Grid.Row="1">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="160"/>
                    <ColumnDefinition Width="*"/>
                </Grid.ColumnDefinitions>
                <Grid.RowDefinitions>
                    <RowDefinition Height="24"/>
                    <RowDefinition Height="*"/>
                </Grid.RowDefinitions>

                <ScrollViewer Grid.Column="0" Grid.Row="1">
                    <ItemsControl Name="TaskPane">
                        ...
                    </ItemsControl>
                </ScrollViewer>

                <StackPanel Name="MainContent" Grid.Column="1" Grid.Row="1" Orientation="Vertical">
                    ...
                </StackPanel>
            </Grid>
        </Grid>

        <ResizeGrip Name="ResizeGrip" Grid.Column="1" Grid.ColumnSpan="2" Grid.Row="1" Grid.RowSpan="2" Foreground="Red" HorizontalAlignment="Right" VerticalAlignment="Bottom" Width="16" Height="16" Padding="0 0 18 18"/>

        <Thumb Name="TopLeftThumb" Grid.Column="0" Grid.Row="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNWSE" DragDelta="TopLeftThumb_DragDelta"/>
        <Thumb Name="TopThumb" Grid.Column="1" Grid.Row="0" VerticalAlignment="Top" Opacity="0" Cursor="SizeNS" DragDelta="TopThumb_DragDelta" />
        <Thumb Name="TopRightThumb" Grid.Column="2" Grid.Row="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNESW" DragDelta="TopRightThumb_DragDelta"/>
        <Thumb Name="LeftThumb" Grid.Column="0" Grid.Row="1" HorizontalAlignment="Left" Opacity="0" Cursor="SizeWE" DragDelta="LeftThumb_DragDelta" />
        <Thumb Name="RightThumb" Grid.Column="2" Grid.Row="1" HorizontalAlignment="Right" Opacity="0" Cursor="SizeWE" DragDelta="RightThumb_DragDelta" />
        <Thumb Name="BottomLeftThumb" Grid.Column="0" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNESW" DragDelta="BottomLeftThumb_DragDelta"/>
        <Thumb Name="BottomThumb" Grid.Column="1" Grid.Row="2" VerticalAlignment="Bottom" Opacity="0" Cursor="SizeNS" DragDelta="BottomThumb_DragDelta" />
        <Thumb Name="BottomRightThumb" Grid.Column="2" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNWSE" DragDelta="BottomRightThumb_DragDelta"/>
    </Grid>
</Border>

I’ve searched online, but can find anything on this. I’ve tried creating another UserControl with a ScrollViewer as the layout root, and get the same error.

Answer 1

By any chance do you have a ScrollViewer style defined in any of your resources somewhere? I saw this link which may be related: http://blog.alner.net/archive/2010/05/07/wpf-style-and-template-resources_order-matters.aspx

The error usually occurs when one style uses a 2nd style, but that 2nd style gets added after the 1st one does. Rather hard error to diagnose.