Converter for DataValidationErrors

[timunie]

What does the pull request do?

Adds a converter attached property to control how DataValidation messages are shown

What is the current behavior?

No easy way to modiy the displayed messages.

What is the updated/expected behavior with this PR?

Easy to use converter attached

How was the solution implemented (if it's not obvious)?

See new sample page

Checklist

• Added unit tests (if possible)? :TODO:
• Added XML documentation to any related classes? :TODO:
• Consider submitting a PR to https://github.com/AvaloniaUI/Documentation with user documentation :TODO:

Breaking changes

Obsoletions / Deprecations

Fixed issues

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0034392-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[timunie]

For reference #11234 (comment)

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0034547-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0034549-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0037161-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0038250-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0039060-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[timunie]

@maxkatz6 I tried your changes and I think these are a useful addition. Now I need to write some docs before 11.1 is released.

Thx ❤️

[timunie]

@maxkatz6 we have a failing test here:

Avalonia/tests/Avalonia.Controls.UnitTests/TextBoxTests_DataValidation.cs

Lines 43 to 65 in e40d5d6

	public void Setter_Exceptions_Should_Set_DataValidationErrors_Errors()
	{
	using (UnitTestApplication.Start(Services))
	{
	var target = new TextBox
	{
	DataContext = new ExceptionTest(),
	[!TextBox.TextProperty] = new Binding(nameof(ExceptionTest.LessThan10), BindingMode.TwoWay),
	Template = CreateTemplate(),
	};
	target.ApplyTemplate();
	Assert.Null(DataValidationErrors.GetErrors(target));
	target.Text = "20";
	IEnumerable<object> errors = DataValidationErrors.GetErrors(target);
	Assert.Single(errors);
	Assert.IsType<InvalidOperationException>(errors.Single());
	target.Text = "1";
	Assert.Null(DataValidationErrors.GetErrors(target));
	}
	}

Do you know how to solve it?