Apply generic types for Combo Change event. Fix silent error for Change event when using T=int.

[skrustev]

Description

• Fix binding to Combo Change event when using T="int" throwing exception silently.
• Add ability to convert value of other related types to specific type, in this case the Combo Change event Value args with specified generic type.
• Apply the generic types for the Combo Value in IgbComboChangeEventArgs and IgbComboChangeEventArgsDetail.
• Refactor some Combo tests to easily test out different types for the Combo values like int/double/string.

Motivation / Context

The above items are quite critical to the normal Combo functioning in Blazor when using different value types and are some needed quality improvements.

Type of Change (check all that apply):

• Bug fix
• New functionality
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (no functional changes)
• Documentation
• Demos
• CI/CD
• Tests
• Changelog

Component(s) / Area(s) Affected:

Combo, Possibly Calendar

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

Test Configuration:

• .NET version:
• Hosting model:
• Browser(s):
• OS:

Screenshots / Recordings

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code
• This PR includes API docs for newly added methods/properties
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes behavioral changes and the feature specification has been updated with them
• Accessibility (ARIA, keyboard navigation, focus management) has been verified

Closes #364

[Copilot]

Pull request overview

This PR updates the Ignite UI for Blazor Combo wrapper to strongly-type the Change event arguments using the combo’s generic type parameter, and adjusts the interop marshalling pipeline so keyed selection values can round-trip correctly (including T=int which previously failed silently).

Changes:

• Made IgbCombo<T>.Change use EventCallback<IgbComboChangeEventArgs<T>>, with Detail.NewValue now typed as T[].
• Updated marshalling/return-value conversion to construct generic combo event args/details and to better transform arrays before downcasting.
• Expanded unit coverage for keyed-value scenarios across int, double, and string keys.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/IgniteUI.Blazor.Tests/ComboTests.cs	Refactors keyed-value contract tests into a generic base and adds coverage for int/double/string key values.
src/componentsBase/MarshalByValueFactory.cs	Adds a generic CreateInstance<T> so combo change event args/details can be created with the correct generic type.
src/componentsBase/BaseRendererElement.cs	Adds generic overloads for conversion helpers and propagates generic conversion to the root control.
src/componentsBase/BaseRendererControl.cs	Improves array transformation/downcast behavior and routes marshal-by-value creation through generic factory.
src/components/Blazor/ComboChangeEventArgsDetail.cs	Makes NewValue strongly typed (T[]) and deserializes it via ReturnToObjectArray<T>.
src/components/Blazor/ComboChangeEventArgs.cs	Makes Detail strongly typed (IgbComboChangeEventArgsDetail<T>) and converts via ConvertReturnValue<T>.
src/components/Blazor/Combo.cs	Updates Change event callback type to the new generic event args and propagates typed value updates.

Suppressed comments (1)

tests/IgniteUI.Blazor.Tests/ComboTests.cs:357

• ComboValueKeyStringTests should override the value-key name to use StringId so the test exercises the string-key path rather than still using the default "Id" key.

public class ComboValueKeyStringTests : ComboValueKeyTestsBase<string>
{
    protected override string EventKeyValue => "\"UK02\"";
    protected override string ExpectedKeyValue => "UK02";
    protected override string[] PropValues => ["UK01", "UK03"];
    protected override string ExpectedValue => """["UK01", "UK03"]""";

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[MayaKirova]

Works fine, but since it changes part of the public API - the type of the event args:
IgbComboChangeEventArgs -> IgbComboChangeEventArgs
This would throw error after update on existing apps.

Maybe we should document all the breaking changes we do here somewhere?

[damyanpetev]

Works fine, but since it changes part of the public API - the type of the event args: IgbComboChangeEventArgs -> IgbComboChangeEventArgs This would throw error after update on existing apps.

Maybe we should document all the breaking changes we do here somewhere?

Valid concern, and if possible how about we avoid the breaking if possible first? When we did IgbCombo<T> as a reminder we couldn't mitigate it - I believe I tested and Blazor was not happy about doubling up the component class, but that might work for the event args. What I mean by that is, C# generics can't have a default value for the type param sadly (like TS can) so you can't init them w/o specifying, but you can define generic-less as concrete version of that, i.e.

IgbComboChangeEventArgs : IgbComboChangeEventArgs<object>

so the old classes

1. still exist with the correct types too
2. can be marked with deprecations if we so choose
3. Should be fairly easy to convert back-forth I hope
   The last bit might be trickier, might need some exploration to see if a direct conversion between the types will work with the new internals and pre-existing app code for example.