StaticViewLocator

A C# source generator that automatically implements static view locator for Avalonia without using reflection.

Usage

Add NuGet package reference to project.

<PackageReference Include="StaticViewLocator" Version="0.3.0">
  <PrivateAssets>all</PrivateAssets>
  <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
</PackageReference>

Annotate a view locator class with [StaticViewLocator], make it partial, and let the generator provide the lookup tables and fallback helpers.

[StaticViewLocator]
public partial class ViewLocator : IDataTemplate
{
    public Control? Build(object? data)
    {
        if (data is null)
        {
            return null;
        }

        var type = data.GetType();
        var func = TryGetFactory(type) ?? TryGetFactoryFromInterfaces(type);

        if (func is not null)
        {
            return func.Invoke();
        }

        var missingView = TryGetMissingView(type) ?? TryGetMissingViewFromInterfaces(type);
        if (missingView is not null)
        {
            return new TextBlock { Text = missingView };
        }

        throw new Exception($"Unable to create view for type: {type}");
    }

    public bool Match(object? data)
    {
        return data is ViewModelBase;
    }
}

The generator emits:

• s_views: resolved mappings from Type to Func<Control>
• s_missingViews: unresolved mappings used for "Not Found: ..." fallback text
• helper methods for exact type lookup, generic type-definition lookup, base-class fallback, and interface fallback

By default, the generated lookup order is:

1. exact runtime type
2. generic type definition for generic runtime types
3. base type chain
4. implemented interfaces in reverse order

Source generator will generate mappings using convention-based transforms. By default:

• namespace ViewModels becomes Views
• type suffix ViewModel becomes View
• generic arity markers are removed from the target view name
• interface prefix I is stripped before resolving the target view name

This allows patterns like:

• MyApp.ViewModels.SettingsViewModel -> MyApp.Views.SettingsView
• MyApp.ViewModels.WidgetViewModel<T> -> MyApp.Views.WidgetView
• MyApp.ViewModels.IDetailsViewModel -> MyApp.Views.DetailsView

public partial class ViewLocator
{
	private static Dictionary<Type, Func<Control>> s_views = new()
	{
		[typeof(StaticViewLocatorDemo.ViewModels.TestViewModel)] = () => new StaticViewLocatorDemo.Views.TestView(),
	};

	private static Dictionary<Type, string> s_missingViews = new()
	{
		[typeof(StaticViewLocatorDemo.ViewModels.MainWindowViewModel)] = "Not Found: StaticViewLocatorDemo.Views.MainWindowView",
	};
}

MSBuild configuration

You can scope which view model namespaces are considered and opt into additional behaviors.

<PropertyGroup>
  <StaticViewLocatorViewModelNamespacePrefixes>MyApp.ViewModels;MyApp.Modules</StaticViewLocatorViewModelNamespacePrefixes>
  <StaticViewLocatorIncludeInternalViewModels>false</StaticViewLocatorIncludeInternalViewModels>
  <StaticViewLocatorIncludeReferencedAssemblies>false</StaticViewLocatorIncludeReferencedAssemblies>
  <StaticViewLocatorAdditionalViewBaseTypes>MyApp.Controls.ToolWindowBase</StaticViewLocatorAdditionalViewBaseTypes>
  <StaticViewLocatorNamespaceReplacementRules>ViewModels=Views</StaticViewLocatorNamespaceReplacementRules>
  <StaticViewLocatorTypeNameReplacementRules>ViewModel=View;Vm=Page</StaticViewLocatorTypeNameReplacementRules>
  <StaticViewLocatorStripGenericArityFromViewName>true</StaticViewLocatorStripGenericArityFromViewName>
  <StaticViewLocatorInterfacePrefixesToStrip>I</StaticViewLocatorInterfacePrefixesToStrip>
</PropertyGroup>

Defaults and behavior:

• StaticViewLocatorViewModelNamespacePrefixes uses ; or , separators and defaults to all namespaces.
• StaticViewLocatorIncludeReferencedAssemblies defaults to false. When true, view models from referenced assemblies are included.
• StaticViewLocatorIncludeInternalViewModels defaults to false. When true, internal view models from referenced assemblies are included only if the referenced assembly exposes them via InternalsVisibleTo.
• StaticViewLocatorAdditionalViewBaseTypes uses ; or , separators and extends the default view base type list.
• StaticViewLocatorNamespaceReplacementRules uses ; or , separators with from=to pairs and is applied sequentially to the view-model namespace when deriving the target view namespace. The default includes ViewModels=Views.
• StaticViewLocatorTypeNameReplacementRules uses ; or , separators with from=to pairs and is applied sequentially to the view-model type name when deriving the target view name. The default includes ViewModel=View.
• StaticViewLocatorStripGenericArityFromViewName defaults to true. When enabled, generic arity markers like `1 are removed from the derived target view name, so WidgetViewModel<T> can map to WidgetView.
• StaticViewLocatorInterfacePrefixesToStrip uses ; or , separators and is applied to interface view-model names before looking up the target view. The default includes I.

These properties are exported as CompilerVisibleProperty by the package, so analyzers can read them without extra project configuration.

Supported resolution features

• Exact type mapping
• Open generic mapping, for example WidgetViewModel<T> -> WidgetView
• Base-class fallback
• Interface fallback
• Configurable namespace replacement rules
• Configurable type-name replacement rules
• Configurable interface prefix stripping
• Configurable additional allowed view base types
• Optional referenced-assembly scanning
• Optional internal view-model inclusion

Notes

• Candidate discovery still starts from types whose names end with ViewModel.
• Missing views do not block fallback resolution. The generator keeps unresolved targets in s_missingViews, so a derived type can still fall back to a base-class or interface mapping before returning a "Not Found" placeholder.
• If you provide custom replacement rules, they take precedence over the built-in defaults.

Default view base types:

• Avalonia.Controls.UserControl
• Avalonia.Controls.Window

Accessibility rules:

• View models in the current compilation are always eligible (subject to namespace prefixes).
• Referenced assembly view models must be public unless StaticViewLocatorIncludeInternalViewModels is enabled and InternalsVisibleTo is configured.

License

StaticViewLocator is licensed under the MIT license. See LICENSE file for details.