TodoApp.Uno fails to build on Skia heads: EventTriggerBehavior could not be found

[adrianhall]

Summary

Discovered while fixing #506's NU1605 restore blocker. Once TodoApp.Uno.csproj restores cleanly (Uno.Sdk bumped 5.4.5 -> 5.6.54), building any Skia-based head fails:

error UXAML0001: The type {using:Microsoft.Xaml.Interactions.Core}EventTriggerBehavior could not be found
error UXAML0001: Processing failed for file .../Views/TodoListPage.xaml

followed by cascading CS1061/CS0103 errors (InitializeComponent, Bindings, NotificationQueue, Splash not found) once the XAML compiler bails out.

This was never surfaced before because restore always failed first (see #506) - this is a separate, pre-existing bug independent of the NU1605/NU1903 package-version issues.

Root cause (confirmed via project.assets.json)

CommunityToolkit.WinUI.Behaviors 8.2.250402 (pinned in samples/todoapp/TodoApp.Uno/Directory.Packages.props) depends on Uno.Microsoft.Xaml.Behaviors.Interactivity.WinUI on non-Windows heads. On every head I could test (net10.0-desktop, net10.0-browserwasm), it resolves to:

Uno.Microsoft.Xaml.Behaviors.Interactivity.WinUI/3.0.0-dev.17.g7c09b9114d

a dev-prerelease build, which appears to be missing the Microsoft.Xaml.Interactions.Core namespace (EventTriggerBehavior, etc.) used in Views/TodoListPage.xaml.

By contrast, on net10.0-windows10.0.26100 the same CommunityToolkit.WinUI.Behaviors package resolves the real package instead:

Microsoft.Xaml.Behaviors.WinUI.Managed/3.0.0

which does include Microsoft.Xaml.Interactions.Core. I was not able to test android/ios/maccatalyst locally (missing workloads), but since they share the same Skia-based rendering path as desktop/browserwasm, they almost certainly hit the same failure.

Impact

Blocks re-enabling the todoapp-uno job in build-samples.yml (see #506) for every head except possibly windows.

Ask

Investigate one of:

1. Find/pin a non-prerelease version of Uno.Microsoft.Xaml.Behaviors.Interactivity.WinUI (or whatever CommunityToolkit.WinUI.Behaviors version pulls one) that includes Microsoft.Xaml.Interactions.Core.
2. Replace the interactions:EventTriggerBehavior usage in Views/TodoListPage.xaml with an Uno-native / cross-platform-safe alternative.
3. Confirm whether this is a known upstream Uno Platform / CommunityToolkit.WinUI.Behaviors issue with an existing fix or tracking issue.

Related

• Investigate resolving NU1903 for Tmds.DBus in Uno desktop sample #506 - fixed the NU1605 restore blocker that was masking this build failure.