`DirectProperty` stored a `EnabledDataValidation` flag in its metadata but also had an `IsDataValidationEnabled` property in `DirectPropertyBase` which was the one used by `AvaloniaObject`. Use the version from metadata so that it can be overridden and remove the flag from `DirectPropertyBase`.
Tests for `AvaloniaObject.IsSet` were in the `Metadata` test class, though `IsSet` has nothing to do with metadata. Moved them into `SetValue` which is more relevant.
`SelectionModel` needs to subscribe to `CollectionChanged` on the items before `ItemsControl` in order for the selection to be correct when we come to setting the selected state.
Because `SelectionModel.Source` isn't subscribed during initialization in `ItemsChanged`, we also need to make sure we don't subscribe `ItemsControl` to the collection changes during initialization. Instead subscribe in `OnInitialized` (this requires a few tests to be rooted in order to be called).
Fixes#4293
In #4218 we imported `IElementFactory` from WinUI which is broadly analogous to a recycling datatemplate for lists. In Avalonia this implement `IDataTemplate` in order to have a common base class for all types of data templates.
The problem with this is that `IDataTemplate` already had a `SupportsRecycling` property which is incompatible with the way recycling is implemented in `IElementFactory`. Instead, introduce an `IRecyclingDataTemplate` to signal data templates that support recycling.
danwalmsley
Steven Kirk
artyom
Dariusz Komosinski
Benedikt Schroeder
Nikita Tsukanov
Andrey Kunchev
Steven Kirk
FoggyFinder