Merge pull request #46 from Redth/dev/visible-item-indices

Implement FindVisiblePositions()

VirtualListView/Apple/VirtualListViewHandler.ios.maccatalyst.cs

@@ -255,4 +255,17 @@ public void InvalidateData()
 		});
 
 	}
+
+	public IReadOnlyList<IPositionInfo> FindVisiblePositions()
+	{
+		var positions = new List<PositionInfo>();
+
+		foreach (var cell in PlatformView.VisibleCells)
+		{
+			if (cell is CvCell cvCell)
+				positions.Add(cvCell.PositionInfo);
+		}
+
+		return positions;
+	}
 }

VirtualListView/Controls/VirtualListView.cs

@@ -402,4 +402,12 @@ public void ViewAttached(PositionInfo position, IView view)
 	void RaiseSelectedItemsChanged(ItemPosition[] previousSelection, ItemPosition[] newSelection)
 		=> this.OnSelectedItemsChanged?.Invoke(this, new SelectedItemsChangedEventArgs(previousSelection, newSelection));
 
+	public IReadOnlyList<IPositionInfo> FindVisiblePositions()
+	{
+#if ANDROID || IOS || MACCATALYST || WINDOWS
+		if (Handler is IVirtualListViewHandler handler)
+			return handler.FindVisiblePositions();
+#endif
+		return [];
+	}
 }

VirtualListView/IVirtualListView.cs

@@ -49,6 +49,8 @@ public interface IVirtualListView : IView
 	void ClearSelectedItems();
 
 	void ScrollToItem(ItemPosition path, bool animated);
+
+	IReadOnlyList<IPositionInfo> FindVisiblePositions();
 }
 
 public enum ListOrientation

VirtualListView/IVirtualListViewHandler.cs

@@ -0,0 +1,8 @@
+namespace Microsoft.Maui;
+
+public interface IVirtualListViewHandler
+{
+#if ANDROID || IOS || MACCATALYST || WINDOWS
+	IReadOnlyList<IPositionInfo> FindVisiblePositions();
+#endif
+}

VirtualListView/Platforms/Android/VirtualListViewHandler.android.cs

@@ -195,4 +195,19 @@ void UpdateHorizontalScrollbarVisibility(ScrollBarVisibility scrollBarVisibility
 
 		recyclerView.HorizontalScrollBarEnabled = newHorizontalScrollVisiblility == ScrollBarVisibility.Always;
 	}
+
+	public IReadOnlyList<IPositionInfo> FindVisiblePositions()
+	{
+		var positions = new List<IPositionInfo>();
+
+		var firstVisibleItemPosition = layoutManager.FindFirstVisibleItemPosition();
+		var lastVisibleItemPosition = layoutManager.FindLastVisibleItemPosition();
+
+		for (var p = firstVisibleItemPosition; p <= lastVisibleItemPosition; p++)
+		{
+			positions.Add(PositionalViewSelector.GetInfo(p));
+		}
+
+		return positions;
+	}
 }

VirtualListView/Platforms/Windows/VirtualListViewHandler.windows.cs

@@ -5,8 +5,10 @@
 using WVisibility = Microsoft.UI.Xaml.Visibility;
 using WFrameworkElement = Microsoft.UI.Xaml.FrameworkElement;
 using WScrollBarVisibility = Microsoft.UI.Xaml.Controls.ScrollBarVisibility;
+using WRect = Windows.Foundation.Rect;
 using Microsoft.Maui.Platform;
 using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Media;
 
 namespace Microsoft.Maui;
 
@@ -187,4 +189,37 @@ void UpdateHorizontalScrollbarVisibility(ScrollBarVisibility scrollBarVisibility
 			_ => WScrollBarVisibility.Auto
 		};
 	}
+
+	public IReadOnlyList<IPositionInfo> FindVisiblePositions()
+	{
+		var positions = new List<PositionInfo>();
+
+		// This gets us all the direct children of our repeater which should be IrElementContainers
+		// The items will not all be visible, since virtualizing causes items to get setup out of view
+		// before being displayed.  We need to check if they are actually visible.
+		var childrenCount = VisualTreeHelper.GetChildrenCount(itemsRepeater);
+
+		for (int i = 0; i < childrenCount; i++)
+		{
+			// See if the child is an IrElementContainer
+			if (VisualTreeHelper.GetChild(itemsRepeater, i) is IrElementContainer irElementContainer)
+			{
+				// Is the item actually visible?
+				if (VisibilityHitTest(irElementContainer, itemsRepeater))
+					positions.Add(irElementContainer.PositionInfo);
+			}
+		}
+
+		return positions;
+	}
+
+	static bool VisibilityHitTest(IrElementContainer element, FrameworkElement container)
+	{
+		var bounds = element.TransformToVisual(container).TransformBounds(new WRect(0.0, 0.0, element.ActualWidth, element.ActualHeight));
+
+		return bounds.Left < container.ActualWidth
+			&& bounds.Top < container.ActualHeight
+			&& bounds.Right > 0
+			&& bounds.Bottom > 0;
+	}
 }

VirtualListView/VirtualListViewHandler.cs

@@ -2,7 +2,7 @@
 
 namespace Microsoft.Maui;
 
-public partial class VirtualListViewHandler
+public partial class VirtualListViewHandler : IVirtualListViewHandler
 {
 	#if ANDROID || IOS || MACCATALYST || WINDOWS
 	public static new IPropertyMapper<IVirtualListView, VirtualListViewHandler> ViewMapper = new PropertyMapper<IVirtualListView, VirtualListViewHandler>(Handlers.ViewHandler.ViewMapper)