Experimental interface IBehavior

[stephenquan]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Description of Change

Note

DISCLAIMER: This PR is for continued discussion only.

This PR is marked as experimental in the title of the PR. Reviewers please be are aware this should not be merged into a minor version or service release branch.

These changes include a breaking API change as IAttachedObject is being made public and VisualElement.Behaviors type is changing from IList<Behavior> to IList<IBehavior>.

Doing so will enable behaviors to be assigned to anything (including VisualElement).

Pull Request Overview (Generated by Copilot):
This PR introduces an experimental IBehavior interface in .NET MAUI to enable behaviors to be assigned to any object, not just those constrained by the concrete Behavior class. The change allows behaviors to inherit from VisualElement while implementing IBehavior, potentially enabling DynamicResource functionality through access to the ResourceDictionary.

Key Changes (Generated by Copilot):

• Introduces public IBehavior and IBehavior<T> interfaces
• Makes IAttachedObject interface public (previously internal)
• Updates VisualElement.Behaviors property type from IList<Behavior> to IList<IBehavior>

Reviewed Changes (Generated by Copilot):

File	Description
src/Controls/src/Core/VisualElement/VisualElement.cs	Changed Behaviors property type from IList<Behavior> to IList<IBehavior>
src/Controls/src/Core/Interactivity/IBehavior.cs	Added new IBehavior and IBehavior<T> interfaces
src/Controls/src/Core/Interactivity/IAttachedObject.cs	Changed IAttachedObject visibility from internal to public
src/Controls/src/Core/Interactivity/Behavior.cs	Updated Behavior and Behavior<T> to implement IBehavior and IBehavior<T> respectively
src/Controls/src/Core/PublicAPI/*/PublicAPI.Shipped.txt	Updated public API surface to reflect new interfaces and changed signatures

Issues Fixed

• See Issue 23578: Behavior bindable property with DynamicResource not supported? #23578
• See Discussion 13691: Behavior bindable property with DynamicResource not supported? #13691

Fixes #

[dotnet-policy-service]

Hey there @@stephenquan! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Copilot]

Pull Request Overview

This PR introduces an experimental IBehavior interface in .NET MAUI to enable behaviors to be assigned to any object, not just those constrained by the concrete Behavior class. The change allows behaviors to inherit from VisualElement while implementing IBehavior, potentially enabling DynamicResource functionality through access to the ResourceDictionary.

Key Changes:

• Introduces public IBehavior and IBehavior<T> interfaces
• Makes IAttachedObject interface public (previously internal)
• Updates VisualElement.Behaviors property type from IList<Behavior> to IList<IBehavior>

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/Controls/src/Core/VisualElement/VisualElement.cs	Changed Behaviors property type from IList<Behavior> to IList<IBehavior>
src/Controls/src/Core/Interactivity/IBehavior.cs	Added new IBehavior and IBehavior<T> interfaces
src/Controls/src/Core/Interactivity/IAttachedObject.cs	Changed IAttachedObject visibility from internal to public
src/Controls/src/Core/Interactivity/Behavior.cs	Updated Behavior and Behavior<T> to implement IBehavior and IBehavior<T> respectively
src/Controls/src/Core/PublicAPI/*/PublicAPI.Shipped.txt	Updated public API surface to reflect new interfaces and changed signatures

[jsuarezruiz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[stephenquan]

The last automated tests had 133 successful checks, but 30 failing tests. When I checked some of the failed test logs such as https://dev.azure.com/xamarin/public/_build/results?buildId=153239&view=logs&j=ac32be84-f58b-5440-705b-7d86d454906c&t=547eb81a-2da0-5d4e-f32b-53e5cde9624a it reports:

Error: System.Exception: The emulator did not finish booting in time.

The failed tests aren't specific to the PR but a problem with the test itself.

[jsuarezruiz]

The test GenericsIssue test is failing in Runtime, SourceGen and XamlC.

System.Reflection.TargetException : Object type System.Collections.Generic.ICollection1[Microsoft.Maui.Controls.IBehavior] does not match target type Microsoft.Maui.Controls.AttachedCollection1[Microsoft.Maui.Controls.Behavior].

Could you review it?