First-class support for custom themes

[gix]

It is currently not possible to use a custom theme as a drop-in replacement for a system theme. While it is possible to style everything, it requires more cumbersome work that is easily missed.

For example:

• Custom styles outside of the custom theme (e.g. local styles in a UserControl) always require an explicit BasedOn="{StaticResource {x:Type ...}}" or else they are based on the system theme.
• Inheritance does not work. Normally ListView without a GridView uses the ListBox style, but providing a custom one is not enough, it has to be explicitly set on the ListView.
• Providing a style for ContextMenu does not style the built-in one of textboxes or scrollbars. A prominent example where this can be seen is Visual Studio:
  

My high-quality Aero themes for WPF use reflection and method hooking to solve these problems (But that's just a brittle hack. In fact, it breaks on .NET Core because tiered compilation makes hooking more difficult.). It does so by replacing System.Windows.SystemResources.FindDictionaryResource, normally responsible for locating the theme resource assembly and style for a given type or resource key, with one that can load custom resource dictionaries.

So my wish would be for adoption of a public API to set policies for resource loading, at least for PresentationFramework.dll.

[Poopooracoocoo]

It makes me sad that this is more than a year old. :(