这个网格应用程序模板如何滚动没有滚动查看器?(c# /XAML Windows 8.1)

我一直在尝试理解scrollviewer，并认为我应该看看微软的8.1网格应用程序模板，其内容延伸到屏幕之外。奇怪的是，在XAML页面中似乎甚至没有 Scrollviewer。谁能告诉我是什么使滚动生效的?

<Page
x:Name="pageRoot"
x:Class="GridApp.GroupedItemsPage"
DataContext="{Binding DefaultViewModel, RelativeSource={RelativeSource Self}}"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:GridApp"
xmlns:data="using:GridApp.Data"
xmlns:common="using:GridApp.Common"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Page.Resources>
    <x:String x:Key="ChevronGlyph">&#xE26B;</x:String>
    <!--
        Collection of grouped items displayed by this page, bound to a subset
        of the complete item list because items in groups cannot be virtualized
    -->
    <CollectionViewSource
        x:Name="groupedItemsViewSource"
        Source="{Binding Groups}"
        IsSourceGrouped="true"
        ItemsPath="Items"
        d:Source="{Binding Groups, Source={d:DesignData Source=/DataModel/SampleData.json, Type=data:SampleDataSource}}"/>
</Page.Resources>
<!--
    This grid acts as a root panel for the page that defines two rows:
    * Row 0 contains the back button and page title
    * Row 1 contains the rest of the page layout
-->
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid.ChildrenTransitions>
        <TransitionCollection>
            <EntranceThemeTransition/>
        </TransitionCollection>
    </Grid.ChildrenTransitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="140"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
    <!-- Horizontal scrolling grid -->
    <GridView
        x:Name="itemGridView"
        AutomationProperties.AutomationId="ItemGridView"
        AutomationProperties.Name="Grouped Items"
        Grid.RowSpan="2"
        Padding="116,137,40,46"
        ItemsSource="{Binding Source={StaticResource groupedItemsViewSource}}"
        SelectionMode="None"
        IsSwipeEnabled="false"
        IsItemClickEnabled="True"
        ItemClick="ItemView_ItemClick">
        <GridView.ItemTemplate>
            <DataTemplate>
                <Grid HorizontalAlignment="Left" Width="250" Height="250">
                    <Border Background="{ThemeResource ListViewItemPlaceholderBackgroundThemeBrush}">
                        <Image Source="{Binding ImagePath}" Stretch="UniformToFill" AutomationProperties.Name="{Binding Title}"/>
                    </Border>
                    <StackPanel VerticalAlignment="Bottom" Background="{ThemeResource ListViewItemOverlayBackgroundThemeBrush}">
                        <TextBlock Text="{Binding Title}" Foreground="{ThemeResource ListViewItemOverlayForegroundThemeBrush}" Style="{StaticResource TitleTextBlockStyle}" Height="60" Margin="15,0,15,0"/>
                        <TextBlock Text="{Binding Subtitle}" Foreground="{ThemeResource ListViewItemOverlaySecondaryForegroundThemeBrush}" Style="{StaticResource CaptionTextBlockStyle}" TextWrapping="NoWrap" Margin="15,0,15,10"/>
                    </StackPanel>
                </Grid>
            </DataTemplate>
        </GridView.ItemTemplate>
        <GridView.ItemsPanel>
            <ItemsPanelTemplate>
                <ItemsWrapGrid GroupPadding="0,0,70,0"/>
            </ItemsPanelTemplate>
        </GridView.ItemsPanel>
        <GridView.GroupStyle>
            <GroupStyle>
                <GroupStyle.HeaderTemplate>
                    <DataTemplate>
                        <Grid Margin="0,0,0,2">
                            <Button Foreground="{ThemeResource ApplicationHeaderForegroundThemeBrush}"
                                AutomationProperties.Name="Group Title"
                                Click="Header_Click"
                                Style="{StaticResource TextBlockButtonStyle}" >
                                <StackPanel Orientation="Horizontal">
                                    <TextBlock Text="{Binding Title}" Margin="0,-11,10,10" Style="{StaticResource SubheaderTextBlockStyle}" TextWrapping="NoWrap" />
                                    <TextBlock Text="{StaticResource ChevronGlyph}" FontFamily="Segoe UI Symbol" Margin="0,-11,0,10" Style="{StaticResource SubheaderTextBlockStyle}" TextWrapping="NoWrap" />
                                </StackPanel>
                            </Button>
                        </Grid>
                    </DataTemplate>
                </GroupStyle.HeaderTemplate>
            </GroupStyle>
        </GridView.GroupStyle>
    </GridView>
    <!-- Back button and page title -->
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="120"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Button x:Name="backButton" Margin="39,59,39,0" Command="{Binding NavigationHelper.GoBackCommand, ElementName=pageRoot}"
                    Style="{StaticResource NavigationBackButtonNormalStyle}"
                    VerticalAlignment="Top"
                    AutomationProperties.Name="Back"
                    AutomationProperties.AutomationId="BackButton"
                    AutomationProperties.ItemType="Navigation Button"/>
        <TextBlock x:Name="pageTitle" Text="{StaticResource AppName}" Style="{StaticResource HeaderTextBlockStyle}" Grid.Column="1" 
                    IsHitTestVisible="false" TextWrapping="NoWrap" VerticalAlignment="Bottom" Margin="0,0,30,40"/>
    </Grid>
</Grid>