One shouldn't call `ClearContainer` on a container that is an item. Adjusted `SelectingItemsControlTests` because selection is actually maintained on move with containers hold their own `IsSelected` state.
Fixes#11128
Which exposes the resize reason and new client size. Required renaming `PlatformResizeReason` to `WindowResizeReason`. Made `TopLevel.HandleResized` method internal.
Allow overriding the default behavior of item containers in styles or in `ItemContainerTheme`. To do this, use `SetCurrentValue` to set the properties, only if the properties are not already set (i.e. from a style). This also requires us to clear the current value when the container is cleared (styles won't be affected as `AvaloniaObject.ClearValue` only clears local or `SetCurrentValue` values).
Rather than using the `ISelectable` interface to communicate container selection from the `SelectingItemsControl` to the container, use the `SelectingItemsControl.IsSelected` attached property, setting it with `SetCurrentValue` so that bindings defined in a style or item container theme can override the selection. Required an extra virtual `ContainerForItemPreparedOverride` method on `ItemsControl`.
- `MenuItem` is a `HeaderedSelectingItemsControl` not a `HeaderedItemsControl` so need to separate logic for that case when preparing items
- Added `HeaderTemplate` to `HeaderedSelectingItemsControl `
- Tweaked logic for selecting header templates: parent's `ItemTemplate` should be used if set (cross-checked with WPF)
- Update menu templates to bind to menu item's `HeaderTemplate`
Fixes#10626Fixes#10718
`ItemsControl` now works more like WPF, in that there are separate `Items` and `ItemsSource` properties. For backwards compatibility `Items` can still be set, though the setter is deprecated. `Items` needed to be changed from `IEnumerable` to `IList` though.
Steven Kirk
Tom Edwards
Emmanuel Hansen
Nikita Tsukanov
Dan Walmsley
amwx
robloo