diff --git a/src/Avalonia.Controls/Generators/ItemContainerGenerator.cs b/src/Avalonia.Controls/Generators/ItemContainerGenerator.cs index 57ed67b508..f2b105c901 100644 --- a/src/Avalonia.Controls/Generators/ItemContainerGenerator.cs +++ b/src/Avalonia.Controls/Generators/ItemContainerGenerator.cs @@ -7,8 +7,8 @@ namespace Avalonia.Controls.Generators /// /// /// When creating a container for an item from a , the following - /// method order should be followed: - /// + /// process should be followed: + /// /// - should first be called if the item is /// derived from the class. If this method returns true then the /// item itself should be used as the container. @@ -19,9 +19,29 @@ namespace Avalonia.Controls.Generators /// - The container should then be added to the panel using /// /// - Finally, should be called. - /// - When the item is ready to be recycled, should - /// be called if returned false. /// + /// NOTE: If in the first step above returns true + /// then the above steps should be carried out a single time; the first time the item is + /// displayed. Otherwise the steps should be carried out each time a new container is realized + /// for an item. + /// + /// When unrealizing a container, the following process should be followed: + /// + /// - If for the item returned true then the item + /// cannot be unrealized or recycled. + /// - Otherwise, should be called for the container + /// - If recycling is supported then the container should be added to a recycle pool. + /// - It is assumed that recyclable containers will not be removed from the panel but instead + /// hidden from view using e.g. `container.IsVisible = false`. + /// + /// When recycling an unrealized container, the following process should be followed: + /// + /// - An element should be taken from the recycle pool. + /// - The container should be made visible. + /// - method should be called for the + /// container. + /// - should be called. + /// /// NOTE: Although this class is similar to that found in WPF/UWP, in Avalonia this class only /// concerns itself with generating and clearing item containers; it does not maintain a /// record of the currently realized containers, that responsibility is delegated to the diff --git a/src/Avalonia.Controls/VirtualizingCarouselPanel.cs b/src/Avalonia.Controls/VirtualizingCarouselPanel.cs index da0ff1eb69..28d6a83309 100644 --- a/src/Avalonia.Controls/VirtualizingCarouselPanel.cs +++ b/src/Avalonia.Controls/VirtualizingCarouselPanel.cs @@ -168,7 +168,13 @@ namespace Avalonia.Controls protected internal override Control? ContainerFromIndex(int index) { - return index == _realizedIndex ? _realized : null; + if (index < 0 || index >= Items.Count) + return null; + if (index == _realizedIndex) + return _realized; + if (Items[index] is Control c && c.GetValue(ItemIsOwnContainerProperty)) + return c; + return null; } protected internal override IEnumerable? GetRealizedContainers() @@ -264,7 +270,6 @@ namespace Avalonia.Controls if (controlItem.IsSet(ItemIsOwnContainerProperty)) { controlItem.IsVisible = true; - generator.ItemContainerPrepared(controlItem, item, index); return controlItem; } else if (generator.IsItemItsOwnContainer(controlItem)) diff --git a/src/Avalonia.Controls/VirtualizingPanel.cs b/src/Avalonia.Controls/VirtualizingPanel.cs index a95d4f1ffa..ed92f30454 100644 --- a/src/Avalonia.Controls/VirtualizingPanel.cs +++ b/src/Avalonia.Controls/VirtualizingPanel.cs @@ -76,6 +76,11 @@ namespace Avalonia.Controls /// The container for the item at the specified index within the item collection, if the /// item is realized; otherwise, null. /// + /// + /// Note for implementors: if the item at the the specified index is an ItemIsOwnContainer + /// item that has previously been realized, then the item should be returned even if it + /// currently falls outside the realized viewport. + /// protected internal abstract Control? ContainerFromIndex(int index); /// diff --git a/src/Avalonia.Controls/VirtualizingStackPanel.cs b/src/Avalonia.Controls/VirtualizingStackPanel.cs index 77268c7831..67ec238ceb 100644 --- a/src/Avalonia.Controls/VirtualizingStackPanel.cs +++ b/src/Avalonia.Controls/VirtualizingStackPanel.cs @@ -3,7 +3,6 @@ using System.Collections.Generic; using System.Collections.Specialized; using System.Diagnostics; using System.Linq; -using System.Reflection; using Avalonia.Controls.Primitives; using Avalonia.Controls.Utils; using Avalonia.Input; @@ -326,7 +325,17 @@ namespace Avalonia.Controls return _realizedElements?.Elements.Where(x => x is not null)!; } - protected internal override Control? ContainerFromIndex(int index) => _realizedElements?.GetElement(index); + protected internal override Control? ContainerFromIndex(int index) + { + if (index < 0 || index >= Items.Count) + return null; + if (_realizedElements?.GetElement(index) is { } realized) + return realized; + if (Items[index] is Control c && c.GetValue(ItemIsOwnContainerProperty)) + return c; + return null; + } + protected internal override int IndexFromContainer(Control container) => _realizedElements?.GetIndex(container) ?? -1; protected internal override Control? ScrollIntoView(int index) @@ -578,7 +587,6 @@ namespace Avalonia.Controls if (controlItem.IsSet(ItemIsOwnContainerProperty)) { controlItem.IsVisible = true; - generator.ItemContainerPrepared(controlItem, item, index); return controlItem; } else if (generator.IsItemItsOwnContainer(controlItem))