InputRadioGroup does not support state preservation for child content

[Sebazzz]

Describe the bug

A InputRadioGroup will always re-render all children and does not support state preservation at all.
The consequence of this, is that focus within a InputRadioGroup will not be retained.

To Reproduce

https://gist.github.com/Sebazzz/dc33bb9e984774407aa9b9644f356cca

Run and click the button. You will see that the child components of the radio button will show a new date, indicating a re-render happens.

Further technical details

• ASP.NET Core version: 5.0

This happens because in OnParametersSet always a new _context is initialized:

aspnetcore/src/Components/Web/src/Forms/InputRadioGroup.cs

Lines 32 to 39 in 368fa1d

	protected override void OnParametersSet()
	{
	var groupName = !string.IsNullOrEmpty(Name) ? Name : _defaultGroupName;
	var fieldClass = EditContext.FieldCssClass(FieldIdentifier);
	var changeEventCallback = EventCallback.Factory.CreateBinder<string?>(this, __value => CurrentValueAsString = __value, CurrentValueAsString);
	_context = new InputRadioContext(CascadedContext, groupName, CurrentValue, fieldClass, changeEventCallback);
	}

In the rendering procedure, this is used as a key value. Always being a new instance, the children will always be deleted and new children created:

aspnetcore/src/Components/Web/src/Forms/InputRadioGroup.cs

Lines 42 to 47 in 368fa1d

	protected override void BuildRenderTree(RenderTreeBuilder builder)
	{
	Debug.Assert(_context != null);
	builder.OpenComponent<CascadingValue<InputRadioContext>>(0);
	builder.SetKey(_context);

Possible fix

_context should be initialized once in the OnInitialized or only be changed if the groupname or other parameters change.

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. Because it's not immediately obvious that this is a bug in our framework, we would like to keep this around to collect more feedback, which can later help us determine the impact of it. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[pranavkm]

FYI @TanayParikh

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[thalaeg]

This is an important issue as it causes the radio button to violate aria spec.
Because you lose focus, the arrow keys become unusable.

[springy76]

In summary everything inherited from InputBase<TValue> is just a big big PITA and will throw smelly vomit at you sooner or later.

Starts with: unable to change bind:event to "oninput"
continues with: unable to call FocusAsync
or: globalization pitas (datetime / floating point)
or: impossible to be used outside of an EditForm/EditContext (why not make it optional?)
open end

Everytime it was used anywhere in our projects it got replaced sooner or later by just plain html or handcrafted components.