[Enhancement] Accessible RadioButton

[rachelkang]

Accessible RadioButton

The RadioButton has much room for improvement in their accessibility.

For starters, we need to:

1. Improve accessibility of RadioButton, especially with ControlTemplate
2. Make RadioButton accessible on iOS, where native equivalents do not exist

We must make them more accessible by ensuring they are both screen reader and keyboard navigable on all platforms.

Considerations

Although the area for improvement here is clear, the solution unfortunately is not. When making custom controls accessible, there are many considerations to be made.

1. Improve accessibility of RadioButton, especially with ControlTemplate

This involves ensuring the buttons are just as accessible with or without the use of a ControlTemplate.
See the current radio button accessibility spike at A11yTools repo, where we begin to explore potential solutions

2. Make RadioButton accessible on iOS, where native equivalents do not exist

Some of the options, thoughts, and questions that we're continuously thinking about:

• If we try to mimic the behavior of RadioButtons as rendered on Safari and/or macOS, how can we approach that implementation? If anyone has any thoughts/advice about this, please do share!
• Should we map it to a "similar" existing native control and have it "behave" like that control natively? (i.e. iOS UISwitch)
• Should we assign our own custom accessibility text? If so, how do we determine that text? And how do we best translate/localize it?
• What pieces of information are essential to announce for accessibility?
  • button content/text --> YES
  • "double to tap activate/check/switch" --> ?
  • "button 1 of 5" grouping info --> ??
  • etc --> ??
• What should the screen reader read for these controls by default?

Related issues / PRs

• [Bug] Serious accessibility issues in RadioButton with a ControlTemplate xamarin/Xamarin.Forms#13505
• Set AccessibilityValue regardings check state xamarin/Xamarin.Forms#12357

[PureWeen]

Radiobutton traited like buttons with the selected trait and then the group label is prefixed