EventToCommand (3.1.1)

Bind View events to ViewModel ICommand properties without code-behind event handlers. EventToCommand and EventBinding use the default Avalonia XML namespace; no additional namespace declaration is required. Commands can come from CommunityToolkit.Mvvm or another MVVM library.

Bind by event name

<Button Content="Save"
        EventToCommand.EventName="Click"
        EventToCommand.Command="{Binding SaveCommand}"
        EventToCommand.CommandParameter="{Binding SelectedItem}" />

In 3.1.1, names resolve through Avalonia's routed event registry, including base control events. Click and ClickEvent are equivalent. Names are case-sensitive. Examples include Loaded, Unloaded, SizeChanged, TextChanged, SelectionChanged, PointerPressed, and DoubleTapped, where the host supports the corresponding event.

For a startup command, bind Loaded on the root view:

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             EventToCommand.EventName="Loaded"
             EventToCommand.Command="{Binding InitializeCommand}">
    <!-- View content -->
</UserControl>

Loaded can fire again when a view is reattached. Guard one-time initialization in your ViewModel when needed. ILifecycleAware.OnLoadedAsync(bool isFirstLoad) is also available for ViewModels wired through Crystal's ViewModelLocator or ViewLocator.

Supply the routed event directly

<Button EventToCommand.RoutedEvent="{x:Static Button.ClickEvent}"
        EventToCommand.Command="{Binding SaveCommand}" />

Use an appropriate XML namespace prefix for a custom event owner. An explicit RoutedEvent takes precedence over EventName, requires no reflective event-field lookup, and initializes the declaring type when its field is accessed. This is useful for custom or attached routed events whose owner has not yet registered its events. Name-based lookup can only find events already registered by the owner or a base type of the host.

Multiple events and event arguments

<Button>
    <EventToCommand.Bindings>
        <EventBinding RoutedEvent="{x:Static Button.ClickEvent}"
                      Command="{Binding SaveCommand}"
                      CommandParameter="{Binding SelectedItem}" />
        <EventBinding EventName="PointerPressed"
                      Command="{Binding PressCommand}"
                      PassEventArgs="True" />
    </EventToCommand.Bindings>
</Button>

When PassEventArgs="True", the event arguments become the command parameter and CommandParameter is ignored. Otherwise, the configured parameter is used. Commands run only when CanExecute(parameter) returns true; a null command does nothing. Both the shorthand and collection syntax can be used on the same control. If both bind the same event, both commands execute.

Property	Purpose
`EventName`	Name of a registered routed event; ordinary CLR `EventHandler` fallback on JIT only
`RoutedEvent`	Explicit routed event; takes precedence over `EventName`
`Command`	ViewModel `ICommand`
`CommandParameter`	Parameter used when `PassEventArgs` is false
`PassEventArgs`	Pass the event arguments instead of the configured parameter
`EventToCommand.Bindings`	Collection of `EventBinding` mappings

Changing an event name or explicit event rebuilds the subscription and removes the previous handler. Collection additions, removals, and replacement update the handlers; replacing a collection also releases its change subscription. Commands and parameters are resolved when the event fires, so updated bindings are used.

Native AOT and upgrading

dotnet add package Crystal.Avalonia --version 3.1.1

Existing routed event name bindings remain valid. Remove event-field DynamicDependency workarounds previously added for LoadedEvent, TextChangedEvent, or similar routed events. No application-side preservation attribute is needed for the registry lookup.

The legacy CLR fallback supports only ordinary EventHandler events on JIT runtimes. It does not support CLR EventHandler<TEventArgs> events. Trimmed JIT applications must preserve their CLR event metadata; Native AOT disables this fallback. An explicit RoutedEvent represents a routed event, not an arbitrary CLR event.

Diagnose a missing binding

Unresolved events produce an Avalonia warning in the Crystal.Avalonia log area. Configure your application's Avalonia logging sink to include warnings. Check the spelling and capitalization, that the host supports the event, and that custom owners registered their events. Prefer an explicit RoutedEvent for custom or attached routed events.