Feature : TextBox error handling

[MatFillion]

To offer error state in textbox, can we use an attachedproperty and use something like
INotifyDataErrorInfo or something similar ?

[Xiaoy312]

the spec for input validation is still under review on MS side: microsoft/microsoft-ui-xaml-specs#26
using INotifiyDataErrorInfo would probably means the control itself has to support, which we probably dont want to touch that, unless it is official
it would be also hard to obtain the binding source/path from the control layer
---
Here is something I have in mind:

string FirstName
IValidationResult FirstNameValidation
  - enum[warning|error]: Level
  - string Reason

FirstNAmeValidation could be updated on FirstName changed (sync), based on rx-subcription (async/magic), or on demand (manual)
we could either:

1. duplicate every textbox styles and add a validation variant of it
2. create a composite of textbox with the info bulb, error message

   we might have some issue to inject Foreground and BorderBrush or make them look good, if the base control template isnt using those property, or the visual state animation isnt animated off them

[MatFillion]

Specs are valid in WinUI 3.0 preview 1 so we should use that! It will need to be implemented in Uno first.

[MatFillion]

Here's the sample in the WinUI gallery https://github.com/microsoft/Xaml-Controls-Gallery/blob/winui3preview/XamlControlsGallery/ControlPages/InputValidationPage.xaml.cs

GitHub

microsoft/Xaml-Controls-Gallery

This app demonstrates the controls available in WinUI and the Fluent Design System. - microsoft/Xaml-Controls-Gallery

[carldebilly]

Related to unoplatform/uno#4839