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[Windows] Implement ItemsUpdatingScrollMode on CollectionView (#15601)
* Implement ItemsUpdatingScrollMode on CollectionView Windows * Unsubscribe before a subscription * Fixed wrong name
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Lines changed: 187 additions & 7 deletions

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‎src/Controls/samples/Controls.Sample/Pages/Controls/CollectionViewGalleries/ScrollModeGalleries/EnumPicker.cs‎

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using System;
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using System.Reflection;
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using Microsoft.Maui.Controls;
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namespace Maui.Controls.Sample.Pages.CollectionViewGalleries.ScrollModeGalleries
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{
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class EnumPicker : Picker
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{
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public static readonly BindableProperty EnumTypeProperty =
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BindableProperty.Create(nameof(EnumType), typeof(Type), typeof(EnumPicker),
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propertyChanged: (bindable, oldValue, newValue) =>
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{
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EnumPicker picker = (EnumPicker)bindable;
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if (oldValue != null)
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{
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picker.ItemsSource = null;
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}
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if (newValue != null)
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{
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if (!((Type)newValue).GetTypeInfo().IsEnum)
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throw new ArgumentException("EnumPicker: EnumType property must be enumeration type");
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picker.ItemsSource = Enum.GetValues((Type)newValue);
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}
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});
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public Type EnumType
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{
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set => SetValue(EnumTypeProperty, value);
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get => (Type)GetValue(EnumTypeProperty);
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}
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}
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}

‎src/Controls/samples/Controls.Sample/Pages/Controls/CollectionViewGalleries/ScrollModeGalleries/ItemsUpdatingScrollModeGallery.xaml‎

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<?xml version="1.0" encoding="utf-8" ?>
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<ContentPage
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xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
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xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
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x:Class="Maui.Controls.Sample.Pages.CollectionViewGalleries.ScrollModeGalleries.ItemsUpdatingScrollModeGallery"
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xmlns:controls="clr-namespace:Maui.Controls.Sample.Pages.CollectionViewGalleries.ScrollModeGalleries"
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Title="ItemsUpdatingScrollMode Gallery">
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<Grid
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RowDefinitions="Auto, *" Margin="20">
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<StackLayout
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Orientation="Horizontal"
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HorizontalOptions="Center">
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<Label
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Text="UpdatingScrollMode: "
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VerticalTextAlignment="Center" />
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<controls:EnumPicker
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x:Name="enumPicker"
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EnumType="{x:Type ItemsUpdatingScrollMode}"
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SelectedIndex="0"
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SelectedIndexChanged="OnItemsUpdatingScrollModeChanged" />
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</StackLayout>
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<CollectionView
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x:Name="CollectionView"
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Grid.Row="1"
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ItemsSource="{Binding Items}">
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<CollectionView.ItemTemplate>
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<DataTemplate>
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<Grid
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Padding="12">
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<Grid.RowDefinitions>
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<RowDefinition Height="Auto" />
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<RowDefinition Height="Auto" />
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</Grid.RowDefinitions>
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<Label
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Text="{Binding Text1}"
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FontAttributes="Bold" />
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<Label
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Grid.Row="1"
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Text="{Binding Text2}"
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FontAttributes="Italic"
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VerticalOptions="End" />
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</Grid>
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</DataTemplate>
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</CollectionView.ItemTemplate>
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</CollectionView>
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</Grid>
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</ContentPage>

‎src/Controls/samples/Controls.Sample/Pages/Controls/CollectionViewGalleries/ScrollModeGalleries/ItemsUpdatingScrollModeGallery.xaml.cs‎

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using System;
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using System.Collections.ObjectModel;
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using System.Threading.Tasks;
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using Microsoft.Maui;
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using Microsoft.Maui.Controls;
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namespace Maui.Controls.Sample.Pages.CollectionViewGalleries.ScrollModeGalleries
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{
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public class ItemsUpdatingScrollModeItem
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{
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public string Text1 { get; set; }
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public string Text2 { get; set; }
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}
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public class ItemsUpdatingScrollModeViewModel : BindableObject
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{
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public ObservableCollection<ItemsUpdatingScrollModeItem> Items { get; private set; } = new ObservableCollection<ItemsUpdatingScrollModeItem>();
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public async Task LoadItemsAsync()
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{
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for (int i = 0; i < 50; i++)
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{
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Items.Add(new ItemsUpdatingScrollModeItem
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{
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Text1 = $"Title {i + 1}",
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Text2 = $"Subtitle {i + 1}",
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});
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await Task.Delay(1000);
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}
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}
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}
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public partial class ItemsUpdatingScrollModeGallery : ContentPage
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{
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ItemsUpdatingScrollModeViewModel _viewModel;
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public ItemsUpdatingScrollModeGallery()
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{
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InitializeComponent();
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BindingContext = _viewModel = new ItemsUpdatingScrollModeViewModel();
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}
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protected override async void OnAppearing()
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{
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base.OnAppearing();
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await _viewModel.LoadItemsAsync();
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}
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void OnItemsUpdatingScrollModeChanged(object sender, EventArgs e)
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{
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CollectionView.ItemsUpdatingScrollMode = (ItemsUpdatingScrollMode)(sender as EnumPicker).SelectedItem;
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}
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}
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}

‎src/Controls/samples/Controls.Sample/Pages/Controls/CollectionViewGalleries/ScrollModeGalleries/ScrollModeGallery.cs‎

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@@ -23,10 +23,12 @@ public ScrollModeGallery()
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{
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descriptionLabel,
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GalleryBuilder.NavButton("Scroll Modes Testing", () =>
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new ScrollModeTestGallery(), Navigation)
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new ScrollModeTestGallery(), Navigation),
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GalleryBuilder.NavButton("ItemsUpdatingScrollMode Gallery", () =>
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new ItemsUpdatingScrollModeGallery(), Navigation)
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}
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}
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};
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}
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}
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}
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}

‎src/Controls/samples/Controls.Sample/Pages/Controls/CollectionViewGalleries/ScrollModeGalleries/ScrollModeTestGallery.xaml.cs‎

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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using System.Threading.Tasks;
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using Microsoft.Maui.Controls;
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using Microsoft.Maui.Controls.Xaml;
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‎src/Controls/src/Core/Handlers/Items/ItemsViewHandler.Windows.cs‎

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public static void MapItemsUpdatingScrollMode(ItemsViewHandler<TItemsView> handler, ItemsView itemsView)
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{
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handler.UpdateItemsUpdatingScrollMode();
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}
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void UpdateItemsUpdatingScrollMode()
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{
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if (PlatformView is null || PlatformView.Items is null)
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return;
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if (VirtualView.ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepScrollOffset)
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{
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// The scroll position is maintained when new items are added as the default,
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// so we don't need to watch for data changes
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PlatformView.Items.VectorChanged -= OnItemsVectorChanged;
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}
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else
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{
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PlatformView.Items.VectorChanged -= OnItemsVectorChanged;
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PlatformView.Items.VectorChanged += OnItemsVectorChanged;
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}
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}
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void OnItemsVectorChanged(global::Windows.Foundation.Collections.IObservableVector<object> sender, global::Windows.Foundation.Collections.IVectorChangedEventArgs @event)
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{
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if (VirtualView is null)
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return;
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if (sender is not ItemCollection items)
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return;
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var itemsCount = items.Count;
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if (itemsCount == 0)
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return;
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if (VirtualView.ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepItemsInView)
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{
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var firstItem = items[0];
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// Keeps the first item in the list displayed when new items are added.
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ListViewBase.ScrollIntoView(firstItem);
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}
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if (VirtualView.ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepLastItemInView)
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{
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var lastItem = items[itemsCount - 1];
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// Adjusts the scroll offset to keep the last item in the list displayed when new items are added.
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ListViewBase.ScrollIntoView(lastItem);
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}
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}
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protected abstract ListViewBase SelectListViewBase();

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