public class GroupObservableCollection<T> : ObservableCollection<T>, IGroupCollection{private List<IList<T>> souresList;private List<int> firstIndexInEachGroup = new List<int>();private List<IGroupHeader> groupHeaders;bool _isLoadingMoreItems = false;public GroupObservableCollection(List<IList<T>> souresList, List<IGroupHeader> groupHeaders){this.souresList = souresList;this.groupHeaders = groupHeaders;}public bool HasMoreItems{get{if (CurrentGroupIndex < souresList.Count){var source = souresList[currentGroupIndex];if (source is ISupportIncrementalLoading){if (!(source as ISupportIncrementalLoading).HasMoreItems){if (!_isLoadingMoreItems){if (this.Count < GetSourceListTotoalCount()){int count = 0;int preCount = this.Count;foreach (var item in souresList){foreach (var item1 in item){if (count >= preCount){this.Add(item1);if (item == source && groupHeaders[currentGroupIndex].FirstIndex==-1){groupHeaders[currentGroupIndex].FirstIndex = this.Count - 1;}}count++;}}}groupHeaders[currentGroupIndex].LastIndex = this.Count - 1;return false;}else{return true;}}else{return true;}}else{if (CurrentGroupIndex == source.Count - 1){if (this.Count < GetSourceListTotoalCount()){int count = 0;int preCount = this.Count;foreach (var item in souresList){foreach (var item1 in item){if (count >= preCount){this.Add(item1);if (item == source && groupHeaders[currentGroupIndex].FirstIndex == -1){groupHeaders[currentGroupIndex].FirstIndex = this.Count - 1;}}count++;}}}groupHeaders[currentGroupIndex].LastIndex = this.Count - 1;return false;}else{return true;}}}else{return false;}}}int GetSourceListTotoalCount(){int i = 0;foreach (var item in souresList){i += item.Count;}return i;}public List<int> FirstIndexInEachGroup{get{return firstIndexInEachGroup;}set{firstIndexInEachGroup = value;}}public List<IGroupHeader> GroupHeaders{get{return groupHeaders;}set{groupHeaders = value;}}public IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count){return FetchItems(count).AsAsyncOperation();}private int currentGroupIndex;public int CurrentGroupIndex{get{int count = 0;for (int i = 0; i < souresList.Count; i++){var source = souresList[i];count += source.Count;if (count > this.Count){currentGroupIndex = i;return currentGroupIndex;}else if (count == this.Count){currentGroupIndex = i;if ((source is ISupportIncrementalLoading)){if (!(source as ISupportIncrementalLoading).HasMoreItems){if (!_isLoadingMoreItems){groupHeaders[i].LastIndex = this.Count - 1;if (currentGroupIndex + 1 < souresList.Count){currentGroupIndex = i + 1;}}}}else{//nextif (currentGroupIndex + 1 < souresList.Count){currentGroupIndex = i + 1;}}return currentGroupIndex;}else{continue;}}currentGroupIndex = 0;return currentGroupIndex;}}private async Task<LoadMoreItemsResult> FetchItems(uint count){var source = souresList[CurrentGroupIndex];if (source is ISupportIncrementalLoading){int firstIndex = 0;if (groupHeaders[currentGroupIndex].FirstIndex != -1){firstIndex = source.Count;}_isLoadingMoreItems = true;var result = await (source as ISupportIncrementalLoading).LoadMoreItemsAsync(count);for (int i = firstIndex; i < source.Count; i++){this.Add(source[i]);if (i == 0){groupHeaders[currentGroupIndex].FirstIndex = this.Count - 1;}}_isLoadingMoreItems = false;return result;}else{int firstIndex = 0;if (groupHeaders[currentGroupIndex].FirstIndex != -1){firstIndex = source.Count;}for (int i = firstIndex; i < source.Count; i++){this.Add(source[i]);if (i == 0){groupHeaders[currentGroupIndex].FirstIndex = this.Count - 1;}}groupHeaders[currentGroupIndex].LastIndex = this.Count - 1;return new LoadMoreItemsResult() { Count = (uint)source.Count };}}}

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    public interface IGroupCollection: ISupportIncrementalLoading{List<IGroupHeader> GroupHeaders { get; set; }int CurrentGroupIndex { get; }}public interface IGroupHeader{string Name { get; set; }int FirstIndex { get; set; }int LastIndex { get; set; }double Height { get; set; }}public class DefaultGroupHeader : IGroupHeader{public string Name { get; set; }public int FirstIndex { get; set; }public int LastIndex { get; set; }public double Height { get; set; }public DefaultGroupHeader(){FirstIndex = -1;LastIndex = -1;}}

    public class MyGroupHeader : IGroupHeader, INotifyPropertyChanged{public string Name { get; set; }public int FirstIndex { get; set; }public int LastIndex { get; set; }public double Height { get; set; }public string GoTo { get; set; }private Visibility _goToButtonVisibility = Visibility.Collapsed;public Visibility GoToButtonVisibility{get { return _goToButtonVisibility; }set{_goToButtonVisibility = value;OnPropertyChanged("GoToButtonVisibility");}}public MyGroupHeader(){FirstIndex = -1;LastIndex = -1;}public event PropertyChangedEventHandler PropertyChanged;void OnPropertyChanged(string propertyName){if (PropertyChanged != null){PropertyChanged(this, new PropertyChangedEventArgs(propertyName));}}}

 <ControlTemplate TargetType="local:GroupListView"><Grid BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}"><ScrollViewer x:Name="ScrollViewer" Style="{StaticResource GroupListViewScrollViewer}" AutomationProperties.AccessibilityView="Raw" BringIntoViewOnFocusChange="{TemplateBinding ScrollViewer.BringIntoViewOnFocusChange}" HorizontalScrollMode="{TemplateBinding ScrollViewer.HorizontalScrollMode}" HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}" IsHorizontalRailEnabled="{TemplateBinding ScrollViewer.IsHorizontalRailEnabled}" IsHorizontalScrollChainingEnabled="{TemplateBinding ScrollViewer.IsHorizontalScrollChainingEnabled}" IsVerticalScrollChainingEnabled="{TemplateBinding ScrollViewer.IsVerticalScrollChainingEnabled}" IsVerticalRailEnabled="{TemplateBinding ScrollViewer.IsVerticalRailEnabled}" IsDeferredScrollingEnabled="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}" TabNavigation="{TemplateBinding TabNavigation}" VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}" VerticalScrollMode="{TemplateBinding ScrollViewer.VerticalScrollMode}" ZoomMode="{TemplateBinding ScrollViewer.ZoomMode}"><ItemsPresenter FooterTransitions="{TemplateBinding FooterTransitions}" FooterTemplate="{TemplateBinding FooterTemplate}" Footer="{TemplateBinding Footer}" HeaderTemplate="{TemplateBinding HeaderTemplate}" Header="{TemplateBinding Header}" HeaderTransitions="{TemplateBinding HeaderTransitions}" Padding="{TemplateBinding Padding}"/></ScrollViewer><ProgressRing x:Name="ProgressRing" Visibility="Collapsed" HorizontalAlignment="Center" VerticalAlignment="Center"/></Grid></ControlTemplate>

                       <Grid Background="{TemplateBinding Background}"><Grid.ColumnDefinitions><ColumnDefinition Width="*"/><ColumnDefinition Width="Auto"/></Grid.ColumnDefinitions><Grid.RowDefinitions><RowDefinition Height="*"/><RowDefinition Height="Auto"/></Grid.RowDefinitions><ScrollContentPresenter x:Name="ScrollContentPresenter" Grid.ColumnSpan="2" ContentTemplate="{TemplateBinding ContentTemplate}" Margin="{TemplateBinding Padding}" Grid.RowSpan="2"/><Grid x:Name="GroupHeadersCanvas" Grid.RowSpan="2" Grid.ColumnSpan="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"/><ContentControl x:Name="TopGroupHeader" Grid.RowSpan="2" Grid.ColumnSpan="2" VerticalAlignment="Top" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch"/><ScrollBar x:Name="VerticalScrollBar" Grid.Column="1" HorizontalAlignment="Right" IsTabStop="False" Maximum="{TemplateBinding ScrollableHeight}" Orientation="Vertical" Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}" Value="{TemplateBinding VerticalOffset}" ViewportSize="{TemplateBinding ViewportHeight}"/><ScrollBar x:Name="HorizontalScrollBar" IsTabStop="False" Maximum="{TemplateBinding ScrollableWidth}" Orientation="Horizontal" Grid.Row="1" Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}" Value="{TemplateBinding HorizontalOffset}" ViewportSize="{TemplateBinding ViewportWidth}"/><Border x:Name="ScrollBarSeparator" Background="{ThemeResource SystemControlPageBackgroundChromeLowBrush}" Grid.Column="1" Grid.Row="1"/></Grid>

         protected override void PrepareContainerForItemOverride(DependencyObject element, object item){base.PrepareContainerForItemOverride(element, item);ListViewItem listViewItem = element as ListViewItem;listViewItem.SizeChanged -= ListViewItem_SizeChanged;if (listViewItem.Tag == null){defaultListViewItemMargin = listViewItem.Margin;}if (groupCollection != null){var index = IndexFromContainer(element);var group = groupCollection.GroupHeaders.FirstOrDefault(x => x.FirstIndex == index || x.LastIndex == index);if (group != null){if (!groupDic.ContainsKey(group)){ContentControl groupheader = CreateGroupHeader(group);ContentControl tempGroupheader = CreateGroupHeader(group);ExpressionAnimationItem expressionAnimationItem = new ExpressionAnimationItem();expressionAnimationItem.VisualElement = groupheader;expressionAnimationItem.TempElement = tempGroupheader;groupDic[group] = expressionAnimationItem;var temp = new Dictionary<IGroupHeader, ExpressionAnimationItem>();foreach (var keyValue in groupDic.OrderBy(x => x.Key.FirstIndex)){temp[keyValue.Key] = keyValue.Value;}groupDic = temp;if (groupHeadersCanvas != null){groupHeadersCanvas.Children.Add(groupheader);groupHeadersCanvas.Children.Add(tempGroupheader);groupheader.Measure(new Windows.Foundation.Size(this.ActualWidth, this.ActualHeight));group.Height = groupheader.DesiredSize.Height;groupheader.Height = tempGroupheader.Height = group.Height;groupheader.Width = tempGroupheader.Width = this.ActualWidth;if (group.FirstIndex == index){listViewItem.Tag = listViewItem.Margin;listViewItem.Margin = GetItemMarginBaseOnDeafult(groupheader.DesiredSize.Height);listViewItem.SizeChanged += ListViewItem_SizeChanged;}groupheader.Visibility = Visibility.Collapsed;tempGroupheader.Visibility = Visibility.Collapsed;UpdateGroupHeaders();}}else{if (group.FirstIndex == index){listViewItem.Tag = listViewItem.Margin;listViewItem.Margin = GetItemMarginBaseOnDeafult(group.Height);listViewItem.SizeChanged += ListViewItem_SizeChanged;}else{listViewItem.Margin = defaultListViewItemMargin;}}}else{listViewItem.Margin = defaultListViewItemMargin;}}else{listViewItem.Margin = defaultListViewItemMargin;}}

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        internal void UpdateGroupHeaders(bool isIntermediate = true){var firstVisibleItemIndex = this.GetFirstVisibleIndex();foreach (var item in groupDic){//top headerif (item.Key.FirstIndex <= firstVisibleItemIndex && (firstVisibleItemIndex <= item.Key.LastIndex || item.Key.LastIndex == -1)){currentTopGroupHeader.Visibility = Visibility.Visible;currentTopGroupHeader.Margin = new Thickness(0);currentTopGroupHeader.Clip = null;currentTopGroupHeader.DataContext = item.Key;if (item.Key.FirstIndex == firstVisibleItemIndex){if (item.Value.ScrollViewer == null){item.Value.ScrollViewer = scrollViewer;}var isActive = item.Value.IsActive;item.Value.StopAnimation();item.Value.VisualElement.Clip = null;item.Value.VisualElement.Visibility = Visibility.Collapsed;if (!isActive){if (!isIntermediate){item.Value.VisualElement.Margin = new Thickness(0);item.Value.StartAnimation(true);}}else{item.Value.StartAnimation(false);}}ClearTempElement(item);}//moving headerelse{HandleGroupHeader(isIntermediate, item);}}}

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        public void StartAnimation(bool update = false){if (update || expression == null || visual == null){visual = ElementCompositionPreview.GetElementVisual(VisualElement);//if (0 <= VisualElement.Margin.Top && VisualElement.Margin.Top <= ScrollViewer.ActualHeight)//{//    min = (float)-VisualElement.Margin.Top;//    max = (float)ScrollViewer.ActualHeight + min;//}//else if (VisualElement.Margin.Top < 0)//{//}//else if (VisualElement.Margin.Top > ScrollViewer.ActualHeight)//{//}if (scrollViewerManipProps == null){scrollViewerManipProps = ElementCompositionPreview.GetScrollViewerManipulationPropertySet(ScrollViewer);}Compositor compositor = scrollViewerManipProps.Compositor;// Create the expression//expression = compositor.CreateExpressionAnimation("min(max((ScrollViewerManipProps.Translation.Y + VerticalOffset), MinValue), MaxValue)");////Expression = compositor.CreateExpressionAnimation("ScrollViewerManipProps.Translation.Y +VerticalOffset");//expression.SetScalarParameter("MinValue", min);//expression.SetScalarParameter("MaxValue", max);//expression.SetScalarParameter("VerticalOffset", (float)ScrollViewer.VerticalOffset);
expression = compositor.CreateExpressionAnimation("ScrollViewerManipProps.Translation.Y + VerticalOffset");////Expression = compositor.CreateExpressionAnimation("ScrollViewerManipProps.Translation.Y +VerticalOffset");//expression.SetScalarParameter("MinValue", min);//expression.SetScalarParameter("MaxValue", max);VerticalOffset = ScrollViewer.VerticalOffset;expression.SetScalarParameter("VerticalOffset", (float)ScrollViewer.VerticalOffset);// set "dynamic" reference parameter that will be used to evaluate the current position of the scrollbar every frameexpression.SetReferenceParameter("ScrollViewerManipProps", scrollViewerManipProps);}visual.StartAnimation("Offset.Y", expression);IsActive = true;//Windows.UI.Xaml.Media.CompositionTarget.Rendering -= OnCompositionTargetRendering;//Windows.UI.Xaml.Media.CompositionTarget.Rendering += OnCompositionTargetRendering;}

expression = compositor.CreateExpressionAnimation("ScrollViewerManipProps.Translation.Y + VerticalOffset");

        public async Task GoToGroupAsync(int groupIndex, ScrollIntoViewAlignment scrollIntoViewAlignment = ScrollIntoViewAlignment.Leading){if (groupCollection != null){var gc = groupCollection;if (groupIndex < gc.GroupHeaders.Count && groupIndex >= 0 && !isGotoGrouping){isGotoGrouping = true;//load more so that ScrollIntoViewAlignment.Leading can go to topvar loadcount = this.GetVisibleItemsCount() + 1;progressRing.IsActive = true;progressRing.Visibility = Visibility.Visible;//make sure user don't do any other thing at the time.this.IsHitTestVisible = false;//await Task.Delay(3000);while (gc.GroupHeaders[groupIndex].FirstIndex == -1){if (gc.HasMoreItems){await gc.LoadMoreItemsAsync(loadcount);}else{break;}}if (gc.GroupHeaders[groupIndex].FirstIndex != -1){//make sure there are enought items to go ScrollIntoViewAlignment.Leading//this.count > (firstIndex + loadcount)if (scrollIntoViewAlignment == ScrollIntoViewAlignment.Leading){var more = this.Items.Count - (gc.GroupHeaders[groupIndex].FirstIndex + loadcount);if (gc.HasMoreItems && more < 0){await gc.LoadMoreItemsAsync((uint)Math.Abs(more));}}progressRing.IsActive = false;progressRing.Visibility = Visibility.Collapsed;var groupFirstIndex = gc.GroupHeaders[groupIndex].FirstIndex;ScrollIntoView(this.Items[groupFirstIndex], scrollIntoViewAlignment);//already in viewport, maybe it will not change view if (groupDic.ContainsKey(gc.GroupHeaders[groupIndex]) && groupDic[gc.GroupHeaders[groupIndex]].Visibility == Visibility.Visible){this.IsHitTestVisible = true;isGotoGrouping = false;}}else{this.IsHitTestVisible = true;isGotoGrouping = false;progressRing.IsActive = false;progressRing.Visibility = Visibility.Collapsed;}}}}