Exposing the `ContentPresenter.Child` in `ItemsControl.LogicalChildren` was causing problems when detaching and reattaching an `ItemsControl` to the logical tree. Instead, expose the `ContentPresenter` itself in effect meaning that `ItemsControl` has a "container" type just like the controls derived from it.
Fixes#3487
`SelectionModel` as ported from WinUI has no information about what changed in a `SelectionChanged` event. This adds that information along with unit tests.
`SelectionModel` as ported from WinUI has no information about what changed in a `SelectionChanged` event. This adds that information along with unit tests.
- #nullable enable
- Make it a `readonly struct`
- Most of the time it will only hold a single `int`, so optimize for the common case by having an `int _index` field
- Make `_path` an array rather than a list as it will be fixed-size
- Implement equality
- Implement operators
The root of our logical tree is denoted by `IStyleRoot` for historical reasons: before #1594, styling was defined in `Avalonia.Styling` but the logical tree was defined in `Avalonia.Controls`. The styling system needed a root but because it was lower-level than the logical tree it had to define its own root type which was then repurposed for use by the logical tree.
Since #1594 the logical tree is defined in `Avalonia.Styling` as well so we might as well call `IStyleRoot` what it is: the logical tree root.
- When detaching set `Parent` to `null` before raising the `DetachedFromLogicalTree` event
- To do this, we need to store the logical root in the control so that e.g. a child control can be detached in a `DetachedFromLogicalTree` handler
- Add `Source` and `Parent` properties to `LogicalTreeAttachmentEventArgs` to give more context on what caused the attachment/detachment
Update `TreeItemContainerGenerator.Index` when a `TreeViewItem` is added to or removed from the logical tree. This ensures that removed `TreeViewItem`s won't try to add duplicate containers to the index.
Fixes#2985
Steven Kirk
Joe Clapis
Dariusz Komosinski
Jumar Macato
Dan Walmsley
Benedikt Schroeder
Andrey Kunchev