Extending GridView with Drag and Drop for Grouping and Variable Sized Items

<common:LayoutAwarePage
    x:Name="pageRoot"
    x:Class="GridViewSamples.Samples.Grouped"
    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:GridViewSamples.Samples"
    xmlns:common="using:GridViewSamples.Common"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Page.Resources>
        <DataTemplate x:Key="ItemTemplate">
            <Grid>
                <Border BorderThickness="1" Height="200" Width="200">
                    <Border.Background>
                        <SolidColorBrush Color="{Binding GroupColor}"/>
                    </Border.Background>
                </Border>
                <Grid Margin="12" Background="#88000000">
                    <Grid.RowDefinitions>
                        <RowDefinition />
                        <RowDefinition Height="Auto"/>
                    </Grid.RowDefinitions>
                    <TextBlock Text="{Binding Id}" Margin="5,5,5,0"/>
                    <TextBlock Grid.Row="1" Margin="5,0,5,5">item</TextBlock>
                </Grid>
            </Grid>
        </DataTemplate>
    </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 Style="{StaticResource LayoutRootStyle}">
        <Grid.RowDefinitions>
            <RowDefinition Height="160"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <!-- Back button and page title -->
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Button x:Name="backButton" Click="GoBack" IsEnabled="{Binding Frame.CanGoBack, ElementName=pageRoot}" Style="{StaticResource BackButtonStyle}"/>
            <StackPanel Grid.Column="1" Margin="10">
                <TextBlock x:Name="pageTitle" Style="{StaticResource PageHeaderTextStyle}" >Grouped GridView</TextBlock>
                <TextBlock FontSize="20" >(GridView doesn't allow to use virtualizing panel as GroupStyle.Panel, so can't use WrapGrid here)</TextBlock>
                <TextBlock FontSize="20" >drag&amp;drop doesn't work</TextBlock>
            </StackPanel>
        </Grid>

        <Grid Grid.Row="1">
            <GridView Margin="10" 
                      AllowDrop="True" CanReorderItems="True" CanDragItems="True" IsSwipeEnabled="True"
                      ItemsSource="{Binding}" ItemTemplate="{StaticResource ItemTemplate}" >
                <GridView.ItemsPanel>
                    <ItemsPanelTemplate>
                        <VirtualizingStackPanel Orientation="Horizontal"/>
                    </ItemsPanelTemplate>
                </GridView.ItemsPanel>
                <GridView.GroupStyle>
                    <GroupStyle>
                        <GroupStyle.HeaderTemplate>
                            <DataTemplate>
                                <Grid Background="LightGray" Margin="0">
                                    <TextBlock Foreground="Black" Margin="10" Style="{StaticResource GroupHeaderTextStyle}">
                                        <Run Text="{Binding Id}"/><Run Text=" group"/>
                                    </TextBlock>
                                </Grid>
                            </DataTemplate>
                        </GroupStyle.HeaderTemplate>

                        <GroupStyle.ContainerStyle>
                            <Style TargetType="GroupItem">
                                <Setter Property="BorderBrush" Value="DarkGray"/>
                                <Setter Property="BorderThickness" Value="2"/>
                                <Setter Property="Margin" Value="3,0"/>
                            </Style>
                        </GroupStyle.ContainerStyle>

                        <GroupStyle.Panel>
                            <ItemsPanelTemplate>
                                <VariableSizedWrapGrid ItemHeight="100" ItemWidth="100"/>
                            </ItemsPanelTemplate>
                        </GroupStyle.Panel>
                    </GroupStyle>
                </GridView.GroupStyle>
            </GridView>
        </Grid>

        <VisualStateManager.VisualStateGroups>

            <!-- Visual states reflect the application's view state -->
            <VisualStateGroup x:Name="ApplicationViewStates">
                <VisualState x:Name="FullScreenLandscape"/>
                <VisualState x:Name="Filled"/>

                <!-- The entire page respects the narrower 100-pixel margin convention for portrait -->
                <VisualState x:Name="FullScreenPortrait">
                    <Storyboard>
                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="backButton" Storyboard.TargetProperty="Style">
                            <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource PortraitBackButtonStyle}"/>
                        </ObjectAnimationUsingKeyFrames>
                    </Storyboard>
                </VisualState>

                <!-- The back button and title have different styles when snapped -->
                <VisualState x:Name="Snapped">
                    <Storyboard>
                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="backButton" Storyboard.TargetProperty="Style">
                            <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource SnappedBackButtonStyle}"/>
                        </ObjectAnimationUsingKeyFrames>
                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="pageTitle" Storyboard.TargetProperty="Style">
                            <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource SnappedPageHeaderTextStyle}"/>
                        </ObjectAnimationUsingKeyFrames>
                    </Storyboard>
                </VisualState>
            </VisualStateGroup>
        </VisualStateManager.VisualStateGroups>
    </Grid>
</common:LayoutAwarePage>