Wrap Panel Virtualization

<UserControl x:Class="MediaAssistant.Controls.MovieMiddlePanel.MovieMiddlePanelView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
             xmlns:cal="clr-namespace:Microsoft.Practices.Composite.Presentation.Regions;assembly=Microsoft.Practices.Composite.Presentation" 
             xmlns:UserControls="clr-namespace:MefBasic.UserControls;assembly=MefBasic" xmlns:Constants="clr-namespace:MediaAssistant.Constants" Background="White">
    <DockPanel>
        <UserControls:CollapsibleContainer Name="CollapsibleContainer" DockPanel.Dock="Top" Background="LightGray" Direction="BottomToTop" 
                                       >
            <UserControls:CollapsibleContainer.Child>
                <Grid Height="260">
                    <ContentControl cal:RegionManager.RegionName="{x:Static Constants:MediaAssistantRegionNames.MovieMiddleTopResion}" ></ContentControl>
                </Grid>
            </UserControls:CollapsibleContainer.Child>
        </UserControls:CollapsibleContainer>
        <Border DockPanel.Dock="Top" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
            <ContentControl cal:RegionManager.RegionName="{x:Static Constants:MediaAssistantRegionNames.MovieMiddleBottomRegion}"/>
        </Border>
    </DockPanel>
</UserControl>