Summary

An interaction can be asked as an observable again, and its handlers can run on a scheduler.

• IInteraction<TInput, TOutput>.Handle(TInput) returns IObservable<TOutput>. Code that holds an interaction through the interface asks the question as it did in ReactiveUI 24. Interaction<,> implements it explicitly.
• Interaction<,>.WhenHandled(TInput) returns the question as a cold observable. Each subscription calls Handle once, so a subclass that overrides Handle still applies. It fails with UnhandledInteractionException when no handler answers.
• new Interaction<TInput, TOutput>(handlerScheduler) runs each handler on that scheduler. Pass the main thread's scheduler so a dialog opens on the UI thread. A null scheduler, like the parameterless constructor, runs handlers on the calling thread.
• Interaction<,>.Handle(TInput) still returns Task<TOutput>. Code written against the current release keeps compiling.

Why

Moving Interaction into ReactiveUI.Binding changed its API by accident.

• In ReactiveUI 24, Handle returned IObservable<TOutput>, and IInteraction declared it.
• The move made Handle return Task<TOutput>, removed it from IInteraction, and dropped the constructor that took a handler scheduler.
• Code upgrading from ReactiveUI 24 that subscribed to Handle, used it in an observable chain, or passed a scheduler no longer compiled.

Breaking changes

A class that implements IInteraction<TInput, TOutput> itself must now implement Handle(TInput), returning IObservable<TOutput>.

• Code that uses or derives from Interaction<,> is unaffected.

How this was verified

Tests cover each new member, including a scheduler that holds handlers until it runs.

• The new examples in bindings/BindInteractionExamples.cs run and print their documented output.
• The Apple target frameworks were built on a Windows host with the Apple workloads. They could not be run.

Notes for the reviewer

The change is in Interactions/IInteraction.cs and Interactions/Interaction.cs.

• The PublicAPI.txt files are regenerated and only add the new members.
• WhenHandled goes through Handle rather than walking the handlers itself, so overrides are honoured. Disposing its subscription drops the answer, but a handler that is already running still finishes. Handle takes no cancellation token to stop it.
• The website quotes examples word for word, so the new ones need adding to its interaction page.

Checklist

• I have read the Contribute guide
• The PR title follows Conventional Commits
• Tests cover this change, or the summary says why they do not
• New or changed public API has XML documentation