[need feedback] Create ToggleGroup control

[jstevans]

This is an early PR for help on next steps -- I saw discussion on #224 that asked for a way to scope groupnames, and it seems like this is what a Control is for.

I'm not extremely familiar with Avalonia/WPF, so could use some feedback on whether this is a good start, and what I need to do to actually have a usable Control (and how to use it).

Ideally, I believe a ToggleGroup should:

• be able to contain arbitrary other Controls
• only allow at-most one ToggleButton within it to be selected at a time, by unselecting all other ToggleButtons whenever one is selected

[grokys]

First of all: sorry for the delay - I've been a bit snowed under recently.

A few small nits regarding getting property names: nameof was added after work was started on Avalonia so we don't yet use it everywhere but it's the preferred way of getting a property name as a string.

Regarding the ToggleGroup control itself: this isn't really what I was imagining. This will only track direct visual children of the ToggleGroup control, which may be enough but my feeling is that a toggle group should instead start a "scope" for all descendant controls.

I think a better way to start off would be to add a GroupName property like in WPF.

Once that is added, then there should be a way to "scope" these group names. I'd imagine this could probably be done as an attached property; we could use a control as you've done here but to me an attached property such as ToggleButton.IsGroupScope="true" would be more similar to other "scope" mechanisms in Avalonia/WPF such as name scopes and focus scopes.

Does that make sense?

[grokys]

I'd prefer just using nameof(IsChecked) here.

[grokys]

Again, use nameof(SelectedItem) here.

[grokys]

This does't seem to have had any further activity so closing for now. Thanks anyway @jstevans!

[robloo]

Probably related to the discussion here microsoft/microsoft-ui-xaml#2310.