Migrate to Avalonia 12

Fabulous 10 uses Avalonia 12. Applications upgrading from Fabulous.Avalonia on Avalonia 11 must update code that uses APIs renamed or removed by Avalonia.

Developer tools

Avalonia 12 replaces Avalonia.Diagnostics with the AvaloniaUI.DiagnosticsSupport package. The Fabulous extension keeps attachDevTools as a compatibility name, but its options overload now accepts an Action<DeveloperToolsOptions>. New code should use attachDeveloperTools:

Window(content).attachDeveloperTools(Action<DeveloperToolsOptions>(fun options ->
    options.Gesture <- KeyGesture(Key.F12)))

The parameterless and KeyGesture overloads are also available under both names.

Renamed control APIs

Avalonia renamed watermark and window-decoration APIs. Update Fabulous modifiers as follows:

Avalonia 11 modifier	Avalonia 12 modifier
watermark	placeholderText
useFloatingWatermark	useFloatingPlaceholder
extendClientAreaChromeHints	windowDecorations

The systemDecorations modifier remains available but now accepts WindowDecorations. Native menu item toggleType now accepts MenuItemToggleType.

Event and binding types

The onGotFocus and onLostFocus callbacks now receive FocusChangedEventArgs. displayMemberBinding now accepts BindingBase instead of IBinding.

Avalonia removed pointer-over-element tracking and menu-item click forwarding from the corresponding controls, so the Fabulous pointerOverElement and enableMenuItemClickForwarding modifiers have been removed.

Virtualized templates

Avalonia 12 changed ITreeDataTemplate.Build to receive an INameScope. Fabulous virtualized collections adopt that contract internally; application code using Fabulous collection builders requires no change. Custom Avalonia data-template implementations must update their Build signature.