How Does This Grid App Template Scroll without a Scrollviewer? (C#/XAML Windows 8.1)

Question

I've been trying to understand Scrollviewers, and thought I'd take a look at Microsoft's template for a Grid App for 8.1, whose content extends off the screen. What's odd is that there doesn't seem to even be a Scrollviewer in the XAML page. Can anyone tell me what is enabling the scrolling?

<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>

Answer 1

If we go check out the default GridView template and look for the ItemsPresenter we see it's embedded in a ScrollViewer at the template level. Since now we know there's one there, if we look up towards the top in the Setter declarations we've got some Properties available to us to interact with that ScrollViewer from the GridView itself by seeing;

<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Disabled"/>
<Setter Property="ScrollViewer.HorizontalScrollMode" Value="Enabled" />
<Setter Property="ScrollViewer.IsHorizontalRailEnabled" Value="False" />
<Setter Property="ScrollViewer.VerticalScrollMode" Value="Disabled" />
<Setter Property="ScrollViewer.IsVerticalRailEnabled" Value="False" />
<Setter Property="ScrollViewer.ZoomMode" Value="Disabled" />
<Setter Property="ScrollViewer.IsDeferredScrollingEnabled" Value="False" />
<Setter Property="ScrollViewer.BringIntoViewOnFocusChange" Value="True" />

So if we wanted that GridView to not scroll anymore we could tell it not to like;

<GridView ScrollViewer.HorizontalScrollBarVisibility="Disabled"/>

since it's set to "Auto" at the template level by default.

That's the thing about templates, sometimes it just takes digging one level deeper. Hope this helps, cheers.