Composition View Locator

Overview

CompositionViewLocator is a component that automatically finds and binds a View to its corresponding ViewModel (presentation logic). It implements the IDataTemplate interface for Avalonia UI and uses the MEF to dynamically resolve views from the dependency container.

How It Works

CompositionViewLocator uses a matching algorithm to find the correct view for a given view model:

Direct Type Match — searches for a view by the ViewModel's full type name
Interface Match — if no direct match is found, searches for views based on the interfaces implemented by the ViewModel
Base Class Hierarchy — if still not found, searches through the base class hierarchy
Fallback — if no view is found, displays a TextBlock with the ViewModel's type name for debugging

The locator only matches the objects implementing IViewModel:

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

Setup

To use CompositionViewLocator, add it to your application's data templates in the app initialization App.axaml.cs file:

_container = containerCfg.CreateContainer();

// Register CompositionViewLocator with Avalonia
DataTemplates.Add(new CompositionViewLocator(_container));

ExportViewFor Attribute

Use the [ExportViewFor] attribute to register a view for a view model in the composition container.

Generic version:

[ExportViewFor<MyFeatureViewModel>]
public partial class MyFeatureView : UserControl
{
    public MyFeatureView()
    {
        InitializeComponent();
    }
}

Non-generic version:

[ExportViewFor(typeof(MyFeatureViewModel))]
public partial class MyFeatureView : UserControl
{
    public MyFeatureView()
    {
        InitializeComponent();
    }
}

Example

Basic View Registration

// ViewModel
public class SearchBoxViewModel : RoutableViewModel
{
    public string SearchText { get; set; }
}

// View
[ExportViewFor<SearchBoxViewModel>]
public partial class SearchBoxView : UserControl
{
    public SearchBoxView()
    {
        InitializeComponent();
    }
}

Troubleshooting

View Not Found

If a view cannot be found, a TextBlock with the view model's type name will be displayed. This helps identify missing view registrations during development.

Make sure to:

Decorate your view class with [ExportViewFor<...>] or [ExportViewFor(typeof(...))]
Verify the composition container is properly initialized

Last modified: 17 December 2025