Merge pull request #15 from Redth/scroll-to-item

Add ScrollToItem

Author: Redth

Sample/VirtualListViewSample/ObservableCollectionPage.xaml

@@ -6,10 +6,10 @@
 	xmlns:local="clr-namespace:VirtualListViewSample"
 	xmlns:vlv="clr-namespace:Microsoft.Maui.Controls;assembly=VirtualListView"
 	Title="ObservableCollectionPage">
-	<Grid RowDefinitions="*,Auto" ColumnDefinitions="*,Auto" Padding="20">
+	<Grid RowDefinitions="*,Auto" ColumnDefinitions="*,Auto,Auto" Padding="20">
 		<vlv:VirtualListView
 			Grid.Row="0"
-			Grid.Column="0" Grid.ColumnSpan="2"
+			Grid.Column="0" Grid.ColumnSpan="3"
 			x:Name="vlv"
 			OnSelectedItemsChanged="vlv_SelectedItemsChanged"
 			SelectionMode="Multiple">
@@ -39,5 +39,6 @@
 
 		<Entry x:Name="entryItem" Grid.Row="1" Grid.Column="0" Placeholder="Item" />
 		<Button Grid.Row="1" Grid.Column="1" Text="Add" Clicked="Button_Clicked" />
+        <Button Grid.Row="1" Grid.Column="2" Text="Scroll To" Clicked="ScrollTo_Clicked" />
 	</Grid>
 </ContentPage>

Sample/VirtualListViewSample/ObservableCollectionPage.xaml.cs

@@ -11,7 +11,7 @@ public ObservableCollectionPage()
 
 		Adapter = new ObservableCollectionAdapter<string>(Items);
 
-		for (int i = 0; i < 10; i++)
+		for (int i = 0; i < 100; i++)
 		{
 			Items.Add($"Item: {i}");
 		}
@@ -61,4 +61,16 @@ private void vlv_SelectedItemsChanged(object sender, SelectedItemsChangedEventAr
 			Items.Remove(item);
 		}
 	}
+
+	private void ScrollTo_Clicked(object sender, EventArgs e)
+	{
+		if (!string.IsNullOrEmpty(entryItem.Text))
+		{
+			var item = Items.FirstOrDefault(i => i.Equals(entryItem.Text, StringComparison.InvariantCultureIgnoreCase));
+
+			var itemIndex = Items.IndexOf(item);
+
+			vlv.ScrollToItem(new ItemPosition(0, itemIndex), true);
+		}
+	}
 }

VirtualListView/Apple/VirtualListViewHandler.ios.maccatalyst.cs

@@ -66,7 +66,7 @@ protected override void ConnectHandler(UICollectionView nativeView)
 			VirtualView?.Scrolled(x, y));
 
 		nativeView.DataSource = dataSource;
-        nativeView.Delegate = cvdelegate;
+		nativeView.Delegate = cvdelegate;
 
 		nativeView.ReloadData();
 	}
@@ -123,6 +123,18 @@ public static void MapSelectionMode(VirtualListViewHandler handler, IVirtualList
 	public static void MapInvalidateData(VirtualListViewHandler handler, IVirtualListView virtualListView, object? parameter)
 		=> handler?.InvalidateData();
 
+	void PlatformScrollToItem(ItemPosition itemPosition, bool animated)
+	{
+		var realIndex = PositionalViewSelector?.GetPosition(itemPosition.SectionIndex, itemPosition.ItemIndex) ?? -1;
+
+		if (realIndex < 0)
+			return;
+
+		var indexPath = NSIndexPath.FromItemSection(realIndex, 0);
+
+		PlatformView.ScrollToItem(indexPath, UICollectionViewScrollPosition.Top, animated);
+	}
+
 	void PlatformUpdateItemSelection(ItemPosition itemPosition, bool selected)
 	{
 		var realIndex = PositionalViewSelector?.GetPosition(itemPosition.SectionIndex, itemPosition.ItemIndex) ?? -1;
@@ -134,7 +146,7 @@ void PlatformUpdateItemSelection(ItemPosition itemPosition, bool selected)
 
 		if (cell is CvCell cvcell)
 		{
-            PlatformView.InvokeOnMainThread(() =>
+			PlatformView.InvokeOnMainThread(() =>
 			{
 				cvcell.UpdateSelected(selected);
 			});

VirtualListView/Controls/VirtualListView.cs

@@ -311,6 +311,9 @@ public void ClearSelectedItems()
 			SelectedItem = null;
 	}
 
+	public void ScrollToItem(ItemPosition itemPosition, bool animated)
+		=> Handler?.Invoke(nameof(ScrollToItem), new object[] { itemPosition, animated });
+
 	public bool SectionHasHeader(int sectionIndex)
 		=> SectionHeaderTemplateSelector != null || SectionHeaderTemplate != null;
 

VirtualListView/IVirtualListView.cs

@@ -43,6 +43,8 @@ public interface IVirtualListView : IView
 	void DeselectItem(ItemPosition path);
 
 	void ClearSelectedItems();
+
+	void ScrollToItem(ItemPosition path, bool animated);
 }
 
 public enum ListOrientation

VirtualListView/Platforms/Android/VirtualListViewHandler.android.cs

@@ -78,6 +78,13 @@ public void InvalidateData()
 		adapter?.NotifyDataSetChanged();
 	}
 
+	void PlatformScrollToItem(ItemPosition itemPosition, bool animated)
+	{
+		var position = PositionalViewSelector.GetPosition(itemPosition.SectionIndex, itemPosition.ItemIndex);
+
+		recyclerView.ScrollToPosition(position);
+	}
+
 	public static void MapHeader(VirtualListViewHandler handler, IVirtualListView virtualListView)
 		=> handler.InvalidateData();
 

VirtualListView/Platforms/Windows/VirtualListViewHandler.windows.cs

@@ -5,6 +5,7 @@
 using WVisibility = Microsoft.UI.Xaml.Visibility;
 using WFrameworkElement = Microsoft.UI.Xaml.FrameworkElement;
 using Microsoft.Maui.Platform;
+using Microsoft.UI.Xaml;
 
 namespace Microsoft.Maui;
 
@@ -86,6 +87,15 @@ public void InvalidateData()
 		UpdateEmptyViewVisibility();
 	}
 
+	void PlatformScrollToItem(ItemPosition itemPosition, bool animated)
+	{
+		var position = PositionalViewSelector.GetPosition(itemPosition.SectionIndex, itemPosition.ItemIndex);
+
+		var elem = itemsRepeater.GetOrCreateElement(position);
+
+		elem.StartBringIntoView(new BringIntoViewOptions() { AnimationDesired = animated });
+	}
+
 	public static void MapHeader(VirtualListViewHandler handler, IVirtualListView virtualListView)
 		=> handler?.InvalidateData();
 

VirtualListView/VirtualListViewHandler.cs

@@ -22,8 +22,28 @@ public partial class VirtualListViewHandler
 
 	public static CommandMapper<IVirtualListView, VirtualListViewHandler> CommandMapper = new(ViewCommandMapper)
 	{
+		[nameof(IVirtualListView.ScrollToItem)] = MapScrollToItem,
 	};
 
+	public static void MapScrollToItem(VirtualListViewHandler handler, IVirtualListView view, object parameter)
+	{
+		if (parameter is ItemPosition itemPosition)
+		{
+			handler.PlatformScrollToItem(itemPosition, true);
+		}
+		else if (parameter is object[] parameters)
+		{
+			if (parameters?[0] is ItemPosition p)
+			{
+				var animated = true;
+				if (parameters?[1] is bool a)
+					animated = a;
+
+				handler.PlatformScrollToItem(p, animated);
+			}
+		}
+	}
+
 	public VirtualListViewHandler() : base(ViewMapper, CommandMapper)
 	{